Veterinary Ophthalmic Surgery

VETERINARY OPHTHALMIC SURGERY

Commissioning Editor: Robert Edwards Development Editor: Veronika Watkins Project Manager: Joannah Duncan Designer: Stewart Larking Illustration Manager: Merlyn Harvey Illustrator: Chartwell

V ETERINARY

OPHTHALMIC SURGERY KIRK N. GELATT

VMD Diplomate, American College of Veterinary Ophthalmologists; Emeritus Distinguished Professor of Comparative Ophthalmology, Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, USA and

JANICE PETERSON GELATT

Gainesville, FL USA

MFA

#

2011 Elsevier Ltd. All rights reserved.

No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). ISBN 978-0-7020-3429-9 British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging in Publication Data A catalog record for this book is available from the Library of Congress Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. With respect to any drug or pharmaceutical products identified, readers are advised to check the most current information provided (i) on procedures featured or (ii) by the manufacturer of each product to be administered, to verify the recommended dose or formula, the method and duration of administration, and contraindications. It is the responsibility of practitioners, relying on their own experience and knowledge of their patients, to make diagnoses, to determine dosages and the best treatment for each individual patient, and to take all appropriate safety precautions. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein.

Printed in China

Contributors

Dennis E. Brooks, DVM PhD Dipl ACVO

Bernhard M. Spiess, DVM Dr Med Vet Dipl ACVO and ECVO

University of Florida College of Veterinary Medicine Department of Small Animal and Large Clinical Sciences Gainesville FL, USA

University of Zurich Veterinary Ophthalmology Zurich Switzerland

Douglas W. Esson, DVM Dipl ACVO

Iowa State University College of Veterinary Medicine Department of Clinical Sciences Ames IA, USA

Eye Care for Animals Tustin CA, USA

Brian C. Gilger, DVM MS Dipl ACVO Department DOCS College of Veterinary Medicine North Carolina State University Raleigh NC, USA

Caryn E. Plummer, DVM Dipl ACVO University of Florida College of Veterinary Medicine Department of Small Animal Clinical Sciences Gainesville FL, USA

R. David Whitley, DVM MS Dipl ACVO

David A. Wilkie, DVM MS Dipl ACVO Ohio State University College of Veterinary Medicine Department of Veterinary Clinical Sciences OSU Veterinary Hospital Columbus OH, USA

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Acknowledgments

We would like to thank the new contributors to this book, including Drs Dennis E. Brooks, Douglas W. Esson, Brian C. Gilger, Caryn E. Plummer, Bernhard M. Spiess, R. David Whitley and David A. Wilkie. We would like to also thank Mr Robert Edwards, Commissioning Editor, and Ms Veronika Watkins, Development Editor, Elsevier Limited, for the opportunity to publish this new edition on

ophthalmic surgery for all animal species. We also would like to acknowledge the comparative ophthalmology faculty members and residents, and Edward O. MacKay, PhD, and Tommy Rinkosky, MS, at the College of Veterinary Medicine, University of Florida, Gainesville, Florida, USA for their assistance and support.

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Preface

When the two volumes (Volume 1: Extraocular procedures, and Volume 2: Corneal and intraocular procedures) of the Handbook of Small Animal Ophthalmic Surgery were published in 1994 and 1995, respectively, they were part of a handbook series published by Pergamon Press, Oxford, UK. Because of their popularity, they were out of print within 4 years. We were then presented with the opportunity to update and consolidate these two handbooks into a single text, Fundamentals of Small Animal Ophthalmic Surgery, which was published in 2001 by Butterworth-Heinemann. Next, we were presented with a third challenge – to develop a comprehensive, all-species ophthalmic surgery text, based on the previous texts, which could be used by veterinary ophthalmologists as well as interested veterinary surgeons and practitioners worldwide. Prior to the two first handbooks, the texts devoted to ophthalmic surgery in animals were limited. The most recent books were the Stereoscopic Atlas of Ophthalmic Surgery of Domestic Animals by Harlan Jensen (CV Mosby, St Louis, MO, USA, 1973), the Atlas of Veterinary Ophthalmic Surgery by Stephen Bistner, Gustavo Aguirre, and George Batik (WB Saunders, Philadelphia, PA, USA, 1977), and Surgical Management of Ocular Disease edited by Mark Nasisse (Veterinary Clinics of North America, WB Saunders, Philadelphia, PA, USA, 1997). Most current information on ophthalmic surgery has been published in comprehensive veterinary ophthalmology texts, and in the crush for space, descriptions are limited to brief summaries of the actual surgical techniques. Since 1994, our Handbook of Small Animal Ophthalmic Surgery (Volumes 1 and 2) and subsequent single text, Small Animal Ophthalmic Surgery, are the only textbooks devoted to eye surgery in animals. Only these ophthalmic surgery textbooks focus on all the dimensions of small animal ophthalmic surgery, stressing the pre-, intra-, and postoperative details. This text, Veterinary Ophthalmic Surgery, consists of all of the different types of extraocular and intraocular surgical procedures that are utilized by veterinarians and veterinary ophthalmologists. The base or model species for all of the surgical procedures is the most popular small animal species presented to veterinarians worldwide – the dog and cat. In addition, in each chapter, special sections are devoted to large animals and special species to describe any modifications of these procedures as well as possible new techniques that have evolved to these species. A considerable amount of this new information is on the equine species. The text is divided into 12 chapters: (1) surgical instrumentation; (2) the operating room; (3) anesthesia for ophthalmic surgery; (4) surgery of the orbit; (5) surgery of

the eyelids; (6) surgery of the nasolacrimal apparatus and tear systems; (7) surgical procedures for the conjunctiva and the nictitating membrane; (8) surgery of the cornea and sclera; (9) surgical procedures of the anterior chamber and anterior uvea; (10) surgical procedures for the glaucomas; (11) surgical procedures of the lens and cataract; and (12) vitreoretinal surgery. Each of the surgery chapters is divided into the relevant surgical anatomy, indications for surgery or other medical therapies, the available surgical procedures, the postoperative management, success rates, and postoperative complications followed by any modifications for large animals and special species. Further reading or selected references are included for each chapter for readers interested in consulting the original publications in all animal species. Each chapter contains information that can benefit the veterinary student and veterinary practitioner interested in ophthalmic surgery and who are attempting to expand and/or improve their surgical skills. This text also contains surgical information for the veterinary ophthalmologist in training or the practicing veterinary ophthalmologist wishing to consult a surgical text for the most recent information. A unique aspect of this text is the availability of a special website (www.Gelattonline.com) of actual eye surgeries performed in clinical patients. These videos will be arranged by eye tissue and will follow the same format described and illustrated in the text. The videos will be periodically augmented, so new videos may be added at any time. Any veterinarian is invited to submit ophthalmic surgery videos (on a CD) directly to me (my address is below). If the video is accepted by the author(s) of the associated chapter and the Publisher, it will be added to the website. This presents a unique opportunity for all readers of this text to become actively involved and part of our effort to expand and improve veterinary ophthalmic surgery for all animal species. A gratis copy of the book will be offered for each successful video.

Kirk N. Gelatt, VMD Diplomate, American College of Veterinary Ophthalmologists, Emeritus Distinguished Professor of Comparative Ophthalmology, P.O. Box 100126 Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610-0126, USA and Janice Peterson Gelatt, MFA Gainesville, FL, USA

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CHAPTER

1

Surgical instrumentation Kirk N. Gelatt

Chapter contents Introduction

1

Surgical instruments for ophthalmic surgeries

11

Design of ophthalmic instruments

1

Instrument care, storage, and sterilization

13

Ophthalmic surgical instruments

2

Ophthalmic sutures and needles

14

Adaptations for large animals and special species ophthalmic surgeries

11

Introduction Since the 1960s magnification has had a major influence on advances in ophthalmic surgery and instrumentation. With magnification of the ophthalmic surgical field, incisions previously deemed quite satisfactory were viewed as irregular, and wound apposition as imperfect. The standard ophthalmic surgical instruments, as observed under 10–20 magnification, were too large and impaired the surgeon’s view of the surgical field. Forceps were viewed to compress and occasionally tear tissues. The standard ophthalmic needle holders grasped the smaller needles poorly, often flattening the curved needles. The working distance between the surgical field and the bottom of the operating microscope limited both the number and the size of ophthalmic instruments. As a result, a second type of ophthalmic instrument evolved – smaller instruments for microsurgery. While surgical instrumentation for extraocular procedures partially utilizes general surgical instruments, surgical instruments for conjunctival, corneal, and intraocular surgical procedures require an investment in both standard size and microsurgical ophthalmic instruments. Both the standard and microsurgical ophthalmic instruments are small and delicate in comparison to the general surgical instruments. Long-term use and optimal surgical results with these ophthalmic instruments necessitate prudent care and use. The investment in the standard, microsurgical or a combination of ophthalmic instrumentation varies with their predicted amount of use. The most important instruments are the corneoscleral and conjunctival scissors, and needle holders; these instruments should be the best available. If microsurgical instruments are selected, tying forceps rather

than needle holders are used for the small ophthalmic sutures, and these thumb forceps should be of high quality.

Design of ophthalmic instruments A large assortment of standard and microsurgical instruments is available to the veterinarian contemplating corneal and intraocular surgery. The basic design of these instruments includes several common construction features that facilitate their intended use. The standard ophthalmic instruments are usually about 120–140 mm long; the microsurgical instruments are about 100 mm long (20–30% smaller). These limitations are related to two factors. First, the instruments must be sufficiently large to be comfortably grasped and manipulated. Secondly, the working distance of most operating microscopes varies with the magnification but is usually between 150 and 250 mm. If the instruments are too large, inadvertent contact and the resultant contamination with the bottom of the operating microscope may occur. The diameters of the handles of most of the ophthalmic spatulas and knives are about 6–7 mm. The width of the handles of the larger needle holders, scissors, and thumb forceps is about 10–12 mm. The shape of these instruments also directly influences their use. Instruments with 5–6 mm diameter handles often have rounded or four or six sides to permit convenient rotation or turning of the handle while grasping the instrument. Instruments that are flat or expand in only one direction, like corneoscleral scissors or the different thumb forceps, have handles that are flat or serrated for grasping with the fingers and limited to no rotation. To facilitate grasping and manipulation of these small

1

Surgical instrumentation

instruments without slipping, the handles are usually serrated, knurled or six-sided to accommodate and limit placement of the fingers on these gripping areas. If these irregular surfaces are too small, the grasp of the instrument may be less than secure. If these serrated areas are too large, the large finger placement area may actually limit manipulation and even snag sutures during tying. All ophthalmic instruments are constructed from high-quality stainless steel or now more often from titanium, with dull surfaces to minimize light reflections. Thumb forceps and scissors for corneal and intraocular procedures are usually hinged with different mechanisms to facilitate their opening. The three most common hinges include the X-hinge, the vertical pin hinge, and the bar hinge (Fig. 1.1). The common X-hinge for scissor blades or needle holder tips is usually joined by small screws or pins, and often the handles converge to become spring mechanisms that maintain the instrument in an open position. With vertical pin hinges, as in iris scissors, the hinge pin is deformed as the scissor blade is closed to act as a spring device to open the blades upon release. The bar hinge is typical of most thumb forceps, and consists of the junction of the base of both handles; tension of these handles closes the forceps blades and release results in the forceps tips opening. All of these hinges are very delicate and, if extended too far, can easily bend or break. Most of the standard and microsurgical ophthalmic instruments are designed for a single purpose. Hence, the standard corneal or intraocular surgical instrument pack includes several instruments. Occasionally, these instruments are designed to perform two or more functions. One example is the tying thumb forceps. Its tip usually includes teeth (1  2) which permit grasping of the cornea and/or conjunctiva. Just proximal to its tip is a flat tying platform to grasp sutures during tying and construction of knots. These multiple purpose forceps are usually heavily used during corneal and intraocular surgical procedures and can easily become malaligned. During microsurgery, the tips of the ophthalmic instruments are often the only parts of these instruments that are visible. In addition, many microsurgical instruments possess angled tips to facilitate their use at higher magnifications, and minimize obstruction of the surgical field.

A

B

Ophthalmic surgical instruments are often developed for specific tasks and functions. As a result, a considerable choice of standard and microsurgical ophthalmic instruments is available. A certain number of these instruments are essential and recommended for different small and large animal ophthalmic surgeries. For convenience, instruments for the different ophthalmic surgical procedures are listed later in the chapter. They include:

• • • • •

Table 1.2 – instruments for orbital surgeries Table 1.3 – instruments for eyelid surgeries Table 1.4 – instruments for conjunctival and corneal surgeries Table 1.5 – instruments for intraocular and cataract surgeries Box 1.1 – instruments for vitreoretinal surgeries.

These instruments are presented in further detail.

Eyelid specula Eyelid specula are used to retract the eyelids and enhance exposure of the conjunctiva, cornea, and globe. The ideal eyelid speculum should be strong enough to retract the eyelids to the maximal amount possible, but sufficiently lightweight to prevent direct pressure on the cornea and globe. The most versatile eyelid speculum for small animals is the wire type. For most breeds of dogs and cats, the Barraquer wire speculum is preferred with 14 mm blades and an overall length of 40 mm (Fig. 1.2). The pediatric size Barraquer speculum may be useful in young and smaller animals; its blades are 11 mm and overall length is 34 mm. In large dogs and large animals a heavier eyelid speculum may be necessary. Eyelid specula, such as the Guyton–Park (14 mm blades and overall length of 85 mm), Castroviejo (15 or 16 mm blades and overall length of 75–82 mm), and Williams (10 mm blades and overall length of 90 mm) can provide maximum exposure of the palpebral fissure (Fig. 1.3). Sometimes for the lid speculum to conform to the eyelid and palpebral curvatures of the horse and cow, the arms of the specula are bent slightly. With all eyelid specula, the blades should extend beneath the eyelid margins for several millimeters to adequately retract the eyelids and reduce the possibility of dislodgement. In some species, like the avian species, the palpebral fissures and eyelids are very small, and a single 4-0 to 6-0 silk suture is placed in each eyelid to keep the lids open.

C

Fig. 1.1 The different hinge mechanisms used for ophthalmic instruments: (A) X-type; (B) vertical pin; (C) bar hinge.

2

Ophthalmic surgical instruments

Fig. 1.2 The pediatric and adult size wire eyelid specula by Barraquer. These inexpensive lid specula are the most versatile and durable for small animals.

Ophthalmic surgical instruments

(Table 1.1). In selecting these tissue forceps, one should handle them individually and use those forceps that ‘feel’ the most comfortable.

Eyelid/chalazion forceps

Fig. 1.3 The Williams eyelid speculum is reserved for large breeds of dogs and large animals to retract the eyelids.

Tissue forceps The different types of ocular tissue have resulted in the development of a large selection of tissue forceps with specialized tips. These tissue forceps vary by tips, shaft, handles, springs, and bar hinge (Fig. 1.4). The handles of these forceps are usually flat with serrations or knurling on the handles to facilitate their grasp. Microsurgical forceps usually have angled tips, and are about two-thirds the total length of standard ophthalmic instruments. The arms of these forceps are hinged at the base, and this hinge provides sufficient tension to maintain the tips about 5–10 mm apart. Upon digital compression, the tissue forceps tips should completely and perfectly contact each other. The tips of many forceps are angulated to prevent blockage of the surgeon’s view during surgery. The major difference of the ophthalmic tissue forceps is their tips, which have highly specialized indications

Bar hinge

Springs

Handles

Highly specialized forceps have been developed for entropion and chalazion surgery. The chalazion forceps have an open and a solid plate on the fellow tips (Fig. 1.5). These tips may be either circular or oval; the latter tips are more versatile as they can be inserted in the palpebral fissure with the oval in either the vertical or horizontal axis. With the forceps clamped to the eyelid, a small lid tumor or chalazion can be excised while pressure from the special plates maintains hemostasis and exact positioning of the eyelid margins and mass.

Conjunctival forceps Forceps to manipulate the bulbar and palpebral conjunctiva generally possess teeth. Small splay-tooth or dog-tooth tips with 1  2 teeth are most useful to grasp the conjunctiva during most manipulations. Excessive tension of the conjunctival tissues with the small tips will often create small tears or ‘button-holes’ of the conjunctival mucosa. These small breaks in the conjunctival mucosal surface are not usually important, but may be significant in certain grafting procedures. The tips of the von Graefe tissue forceps possess 10–14 fine teeth and generally accommodate considerable tension of the conjunctival mucosa or the leading edge of the nictitans before tearing is evident (Fig. 1.6). Unfortunately, the von Graefe tips are too large for microsurgical procedures. The conjunctival tissues can also be manipulated with serrated tips, devoid of any teeth; however, slippage of the tips from the mucosa is likely.

Corneal, limbal, and scleral forceps The cornea, sclera, and limbus represent the fibrous tunics of the globe and are remarkably tough tissues to incise, manipulate, and suture. As a result, the tips of the corneal or corneoscleral forceps generally possess some type of teeth. Generally the tips consist of either splay-tooth or dog-tooth designs. These types of tips successfully grasp and hold these tissues. Modifications of these tips, such as the closed-cups (von Mandach forceps) and open-cups (Pierse type), are less traumatic to the cornea, but permit limited lateral slippage.

Suture and tying forceps Shafts

X-hinge Tips

Fig. 1.4 Components of ophthalmic forceps include: tips, shaft, handles, springs and bar/X-hinge.

Special forceps have been developed to facilitate suture manipulation and tying during microsurgery. The tying of small diameter sutures requires suture tying forceps but not the standard or microsurgery needle holder which allows these very small diameter sutures to easily slip within the needle holder jaws. The surgeon’s fingers cannot be used as the sutures are too small and often too short. The standard suture-tying forceps is either the straight or curved model with 1  2 teeth or without teeth. The smooth platforms of both tips have rounded edges to accommodate the sutures and prevent any suture breakage or etching (Fig. 1.7). The platforms

3

1

Surgical instrumentation

Table 1.1 Tips of tissue forceps used for corneal and intraocular surgery

Tip design

Designated tissue(s) or use

Von Graefe

Conjunctiva/nictitans

Appearance

Tip design

Designated tissue(s) or use

Lens capsule Extracapsular

Grasp/tear anterior lens capsule

Splay

Intracapsular

Grasp/hold anterior lens capsule

Dog-toothed

Utrata

Anterior capsulorhexis

1  2 teeth

Appearance

Cornea/conjunctiva

Colibri style tip angulation

Cornea/conjunctiva

Intraocular

Grasp/remove lens capsule and fragments

Serrations

Cornea/conjunctiva

Combination 1  2 teeth tying platform

Cornea/conjunctiva and tying sutures

Tying platforms

Tying small sutures

must meet perfectly flush to permit suture manipulation and grasp during tying. These forceps are designed for the very small size ophthalmic sutures (6-0 to 12-0). The addition of 1  2 teeth to the tip of the Harm-type suture-tying forceps permits these forceps to both grasp corneal or conjunctival

Fig. 1.5 The Francis chalazion (top) and Desmarres entropion (bottom) forceps have specialized tips consisting of an oval to round ring and a solid oval to circular tip. The ring base is used to surround the surgical site, and the solid base is used to protect deeper tissues including the eye.

4

Fig. 1.6 Graefe fixation (top) and cilia (bottom) forceps. The Graefe forceps have wide jaws with multiple fine teeth that can grasp the eyelid and conjunctiva without tearing. The cilia forceps have smooth surface jaws that permit grasping of fine cilia.

Ophthalmic surgical instruments

Fig. 1.7 Tying forceps have shafts with smooth platforms to provide flat surfaces to grasp fine suture material during tying. Some tying forceps have combination shafts with distal 1  2 teeth to grasp tissues, and a more proximal smooth tying platform to grasp sutures. Top: O’Gawa–Castroviejo tying forceps; bottom: Castroviejo suturing forceps.

tissues as well as assist in the tying of sutures, and decreases the time and effort during wound apposition. A unique design, the Colibri style, has been used with many tissue forceps to incorporate a tying platform. Often these Colibri-type forceps, with a characteristic angled shaft, have tips with teeth to assist in the grasping of corneal and conjunctival tissues (Fig. 1.8). The tips with different types of teeth are used to grasp tissues; the knee or angle portion can be used as smooth forceps.

surgery in the dog and cat. Intracapsular lens forceps are used to grasp and hold the anterior lens capsule during removal of the entire lens with its capsules (see Table 1.1). The forceps have slender shafts and tips to enter the anterior chamber and pupil. The shafts are also curved or angled to traverse the pupil and facilitate grasping of the anterior lens capsule. Within the tip is a 2.0–2.5 mm cup to grasp, but not tear, the central anterior lens capsule. The extracapsular forceps are very similar in design, but their tips possess either four or five, or five or six, fine teeth to grasp and tear a central portion of the anterior lens capsule (see Table 1.1). Through the defect in the anterior lens capsule, the remainder of the lens cortex and nucleus are expressed or removed by phacoemulsification. Phacoemulsification has largely replaced the standard extracapsular cataract techniques in most animal species in most countries, and circular tearing of the anterior capsule sufficiently large to accommodate the insertion of an intraocular lens (IOL) has become standard. The most frequently used forceps for continuous anterior capsulectomy or capsulorhexis is the Utrata instrument. The Utrata forceps has variable length tips and very small single teeth pointing down from the two tips to grasp the anterior lens capsule. For additional information on the Utrata forceps, see Chapter 11 on surgery of the lens and cataract.

Iris forceps The animal iris and ciliary body tissues are highly friable and vascular. Excessive traction with tissue forceps on the iris results in frequent tearing and hemorrhage. Iris forceps may be straight or curved; their tips are serrated or possess very small teeth. To facilitate anterior chamber manipulations, the tips and shafts of these forceps are quite slender and delicate.

Anterior lens capsule forceps Special forceps have been developed to grasp and hold or grasp and tear the anterior lens capsule during cataract

Intraocular lens instrumentation With the advent of intraocular lenses (IOLs) in humans and animals, special IOL forceps shaped as either tissue forceps or scissors have been developed. These forceps are used to grasp the IOL or its haptic loop, and facilitate the placement of the IOL within the capsular bag or in the posterior chamber. It is important that these tips do not damage the IOL or its surface during insertion. Both hard (polymethylmethacrylate (PMMA) and acrylic) and foldable (silicone and hydrogel) IOLs have been available for the dog for several years, but only recently for the horse and cat. Several IOL instruments have been developed to position and manipulate IOLs within the anterior chamber, the posterior chamber, and the capsular bag. Most IOLs in the dog are placed in the capsular bag after all cataractous material has been removed. Placement of the IOL usually requires a special forceps; another instrument is used to rotate or dial the IOL into its final position. The IOL hook and lens manipulator possess different tips, with single or forked prongs, that can push the IOL haptics into the final position. With the introduction of the recent soft or foldable IOLs for the dog (which permit a smaller corneal incision), new forceps to fold or roll the IOL during insertion through the corneal incision and into the capsular bag, or an injector or insertor were introduced. Each foldable IOL has a specific instrument to insert that particular type of IOL.

Intraocular forceps Fig. 1.8 The distinctive Colibri forceps have a characteristic angled shaft. Top: Troutman–Barraquer corneal fixation forceps – 0.5 mm 1  2 teeth with a 6 mm tying platform; middle: Troutman–Barraquer corneal fixation forceps – 0.5 mm 1  2 teeth; bottom: Pierse type Colibri forceps (0.03 mm Pierse type tips).

Special intraocular forceps have been developed to grasp and remove tissues or foreign bodies within the anterior chamber, posterior chamber, and within the vitreous (Fig. 1.9). The intraocular forceps have 1.5–2.0 mm jaws and long shafts. The shafts are also small in diameter (20 g needle diameter; 0.89 mm) to accommodate insertion into

5

1

Surgical instrumentation

Fig. 1.9 The intraocular forceps is designed to be inserted through a very small opening. Insert shows the different available tip types.

the different compartments of the globe. The Rappazzo intraocular forceps has smooth, cusp or dusted jaws with a 45 angulation. The Storz intraocular forceps has 1.5 mm cup-shaped oval jaws. Both of these intraocular forceps are used in animals to grasp and remove portions of the anterior lens capsule and portions of the lens cortex and nucleus.

Scissors Because of the different ocular tissues, several specific types of scissors have been developed. No single scissors can perform adequately on the wide range of ocular tissues that one commonly confronts. As a result, specific-use scissors have been designed for the conjunctiva, cornea, corneosclera, iris, and intraocular tissues. Corneal and corneoscleral scissors are available as either standard size or microsurgical scissors. The overall length of the scissors’ ring handles is about 100– 110 mm, and the blades are about 18–20 mm long.

Conjunctival scissors Conjunctival scissors include tenotomy, strabismus, eye, conjunctival, and utility types, and are available with either straight or curved tips (Fig. 1.10). The tips are also varied with both sharp (pointed) and blunt, or a combination of

Fig. 1.10 Selected scissors for conjunctival tissues with either straight or curved blades with sharp or blunt tips. Top: Knapp straight strabismus scissors; middle: Steven’s straight tenotomy scissors; bottom: Steven’s curved tenotomy scissors.

6

both. The handles are ribbon style, ring type, or flat serrated spring-type handles; the latter types are more expensive. My preference is the versatile Steven’s tenotomy scissors with slightly curved, blunt-tipped blades. Conjunctival scissors with blunt tips tend to reduce the likelihood of producing ‘button-holes’ or small full-thickness defects in the bulbar conjunctiva during preparation of conjunctival flaps. These scissors may also be used to cut sutures. As most types of ophthalmic suture are very small, one pair of scissors within each surgical pack just to cut sutures is recommended. The scissors to cut sutures often have pointed and sharp tips, and can be easily distinguished from conjunctival tissue scissors.

Corneal scissors Corneal scissors are available as either standard size or microsurgical types. Because dog and cat corneas are difficult to cut, these scissors should be of high quality to ensure precise incisions and minimal tissue trauma. Periodic sharpening of these scissors may ensure long-term use. A large selection of corneal scissors is available (Fig. 1.11). These scissors can be used as a universal type or as pairs (right and left). The mirror-image pair types of corneal scissors complement each other, and are used to extend corneal incisions in opposite directions. The standard scissors range in total length from about 100 to 120 mm long.

Fig. 1.11 Castroviejo corneal section scissors (right and left) for keratectomy and keratoplasty. These scissors with curved blades are to cut the cornea or limbus; the lower blade is slightly longer to retain the scissors within the anterior chamber during cutting.

Ophthalmic surgical instruments

Microsurgical corneal scissors are about 90 mm long. The tips may be straight, slightly curved, or angled. Both tips may be of equal length, or the bottom tip that is inserted beneath the cornea can be 0.5–1.0 mm longer to maintain the scissor tip within the anterior chamber as multiple cuts are performed. Corneal scissors used for keratoplasty possess tips that are quite curved (5 mm radius) and short as the standard full-thickness corneal graft for humans is usually 6–8 mm diameter. Corneal scissors used at the limbus have longer tips. These scissors may cut either vertically or obliquely. For most corneal incisions, vertical rather than oblique incisions are preferred, unless the incision is close to the limbus. To achieve a vertical cut, the lower blade of the corneal scissors is hinged to contact the inside of the concavity of the upper blade.

Corneoscleral or corneal section cataract scissors Corneoscleral scissors are the larger corneal scissors that are used at the limbus. Corneoscleral scissors, like corneal scissors, are available as either standard or microsurgical types (Fig. 1.12). These scissors are usually self-opening with the flexible handles functioning as springs and loosely connected at their ends. Some of these types of scissors have one rigid handle and the opposite flexible handle to maintain the scissors’ blades in an open position. Still other models look like regular scissors with straight handles. Standard corneoscleral scissors are about 100–120 mm long, and have slightly angled and curved tips. The tips are about 12–20 mm long and often the bottom blade is 0.5–1.5 mm longer to maintain the tip within the anterior chamber during repeated cuts of the limbus. In most corneoscleral or cataract section scissors the lower blade cuts against the convex curve of the upper blade, producing an oblique cut. These scissors are used to cut the cornea, limbus, and sclera, to perform keratoplasty, and often in animals to enter the anterior chamber during cataract surgery. For maximum flexibility, a slightly angled curved right and left pair of corneal section scissors is recommended. As most cataract surgery in animals uses a clear corneal incision for entry into the anterior chamber, these scissors should be of high quality for maximum durability.

Fig. 1.12 Castroviejo corneal section cataract scissors (right and left) for entry into the anterior chamber at the periphery cornea or limbus.

Iris scissors The animal iris is a very friable and vascular tissue, which upon incision will often hemorrhage extensively. As a result, incision of the iris often necessitates cautery before or after cutting to seal these vessels. Iris scissors are small and delicate, and are designed to cut the iris on a flat surface. As these scissors must be very sharp, their use should be limited to cutting only iridal tissues. Iris scissors include types by Vannas, DeWecker, and Barraquer, as well as the traditional ophthalmic scissors with ring or curled handles (Fig. 1.13). Their tips are usually pointed and slightly angled. The specialized Vannas and Barraquer iris scissors are quite small (54 mm long); the DeWecker iris scissors are 114 mm long. They can be easily inserted into the anterior chamber to perform a dorsal iridectomy or sphincterotomy. Because of the increased vascularity of most animal basal irides, incision/ excision of the iris is usually performed with the involved part of the structure extended from the anterior chamber or avoiding the basal iris. Limited electrocautery may be necessary to obtain complete hemostasis after incision of the iris and before repositioning into the anterior chamber.

Intraocular scissors With refinement of intraocular surgical techniques, small scissors were developed to cut intraocular tissues often through small corneal, limbal, or scleral incisions, or the pupil. There are two basic types: 1) standard ophthalmic scissors that can be inserted through a complete corneal or corneoscleral incision with 10–15 mm long and very slender blades; and 2) intraocular scissors constructed like the intraocular forceps with a shaft diameter of about 1.0 mm (the outside diameter of a 20 g hypodermic needle). The intraocular scissors’ handles may be spring type, barrel-squeeze type, or the traditional rigid curled handles (Fig. 1.14). The tips are usually pointed, and close as regular scissors or like a guillotine type. The blades of scissors inserted through 2 or 3 mm corneal or limbal incisions range from 1 to 3 mm long. More recently a subtype of intraocular scissors has been developed to insert through limbal or corneal incisions to cut the anterior lens capsule. These microsurgical capsulotomy scissors possess either straight or slightly angled

Fig. 1.13 Special scissors for cutting the iris. Top: Barraquer iris scissors; bottom: McPherson–Vannas curved iris scissors.

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Surgical instrumentation

Fig. 1.14 Intraocular scissors: Storz intraocular scissors; the straight blades are 3.0 mm long and pointed. Insert: close-up of the cutting blades.

pointed blades of 5–11 mm long. The tips of these scissors must be very sharp and their function limited to anterior capsulotomies or capsulectomies.

Instruments used during phacoemulsification When phacoemulsification was first introduced in the 1970s by Kelman, the phaco surgery involved one larger corneoscleral incision for the phaco handpiece (which provided the ultrasonic energy and aspiration) and a separate smaller incision about 90 to the larger incision to insert the infusion needle (balanced salt solution for the anterior chamber was provided by gravity from a bottle on an intravenous stand). Today’s phaco tips possess all three of these functions: 1) aspiration to remove lens material and aqueous humor; 2) infusion to regulate the amount of irrigating solution delivered to the phaco site; and 3) phaco (ultrasonic) energy to fragment and break down the lens material through a single incision. New instruments (quick chopper, nucleus segmenter, prechopper, etc.) have now been developed to assist phacoemulsification by stabilizing as well as chopping (incise and divide) the hard lens nucleus, and these instruments are generally inserted through a second smaller corneal incision, returning to the bimanual phacoemulsification of the 1970s. They are also inserted into the lens nucleus to lift as well as support lens fragments toward the phaco tip for fragmentation. An example is the Steinert nuclear chopping instrument which possesses an angular tip with a wedge-like end (1.5 mm) sharpened on its inner edge. This creates the chop of the nucleus while maintaining contact of the chopper with the nucleus; deep penetration of the nucleus is avoided, thus preventing posterior capsule penetration. Another intralens instrument is similar to a wire hook. Warren (see Further reading) modified the Nagahara technique used in humans for the dog. This procedure uses the phaco tip to impale and, with high vacuum, hold the lens nucleus while a chopper is hooked at the lens equator and pulled centrally, splitting the nucleus along its natural cleavage planes. By dividing the nucleus into quadrants or smaller parts using the chop technique, and combined with the phacoemulsification ‘divide and conquer’ technique, phaco time and energy are significantly reduced, as is corneal endothelial cell damage. Since the dog’s lens is larger than the human, Warren recommends using the human instrument for small dogs (1–2 mm tip) and has modified the Chang combination

8

chopper for medium and large dogs (4 mm tip). For safety, the chopper’s tip is inserted into the nucleus to only one-half thickness. Some canine cataract cortices and nuclei are too hard to ‘chop’ or possess insufficient room for the instrument to pass between the anterior lens capsule and adjacent cortex, and are not amenable to this technique. Additional information on chop techniques is found in Chapter 11.

Knives The dog and cat cornea, limbus, and sclera are very tough tissues, and will dull most stainless steel knives after only a few incisions. As a result, disposable blades are usually employed to ensure a sharp and atraumatic incision. The Beaver or BD Nos 6400, 6500, and 6700 microsurgical blades (Bectin, Dickinson and Company, Franklin Lakes, NJ) are the most often used (Fig. 1.15). The Beaver No. 6400 blade with the traditional shape is used to incise the cornea, limbus, and sclera. As an alternative, the Beaver No. 6700 blade has a more pointed tip and is used for the same incisions. The Beaver No. 6500 blade is pointed and used to incise the full-thickness of the cornea, limbus, and sclera. The Beaver keratomes are preferred to incise the cornea and the anterior lens capsule during cataract surgeries in small animals. This blade is arrow-shaped, and as it is pushed through the cornea or limbus, both of its sides incise the full-thickness corneal, limbal or scleral tissues. The incisions tend to self-seal, but in animals they are often apposed by sutures. The larger Bard–ParkerTM Nos 11 (pointed) and 15 scalpel blades and handle are not designed as microsurgical instruments. They are reserved for eyelid and orbital surgeries in both small and large animals.

Fig. 1.15 BeaverTM or BD microsurgical blades (Bectin, Dickinson and Company, Franklin Lakes, NJ): Left: top, No. 6400; middle, No. 6500. Right: top, No. 6700; middle, keratome. Bottom: Beaver or BD scalpel handle.

Ophthalmic surgical instruments

Diamond knives were introduced several years ago, as a reusable scalpel blade and handle. This knife is used for corneal, limbal, and scleral incisions. A micrometer has been added to some types of diamond knives to control the length of the blade, and to perform corneal refractive surgery. The diamond blade shape ranges from an angle, to spear-like to rounded, and is 1.0–3.0 mm wide. These high-cost blades are very sharp, and must be carefully used, cleaned, and stored. Although a corneal dissector and restricted depth knife are not scalpel blades per se, these instruments are used to bluntly separate the corneal stromal layers. The corneal separators, like the Martinez and Gill corneal dissector knives, are used to dissect the different layers of the corneal stroma and reduce greatly the risk of progressive deeper separation of the cornea and corneal penetration.

Needle holders Needle holders are very important in ophthalmic surgery, as considerable time is consumed during the apposition of surgical incisions. Needle holders are available as either the standard models or the smaller microsurgical types (Fig. 1.16). Their tips are also divided into delicate, fine, medium, and heavy duty. The standard size needle holders are about 120–130 mm long, and the microsurgical types are about 100 mm long. The most common shape is similar to that of the corneal and corneoscleral scissors with flexible serrated or knurled handles which are joined to provide a spring mechanism that automatically maintains the needle holder tips in the open position. Ophthalmic needle holders are designed to be held as a pencil. For general extraocular surgery, the Castroviejo needle holder with flat serrated handles and a lock is often used. The jaws are about 9 mm long and may be straight or gently curved. For microsurgery involving the cornea, the Storz or Barraquer needle holder with curved jaws and no locks is preferred. All of the ophthalmic needle holders are designed for only the small ophthalmic needles and sutures. Large needles and sutures larger than 4-0 will gradually distort these needle holder’s jaws, rendering the instrument useless; hence, these instruments are not useful for tying the very fine ophthalmic sutures (special tying forceps are used instead). The straight to curved tips are 7–16 mm long, and their surfaces may be smooth or serrated.

Fig. 1.16 Top: Smaller microsurgical needle holder (made of titanium and 109 mm long) with no lock and curved 9 mm fine jaws. Bottom: Standard Castroviejo needle holder (130 mm long) with lock and curved 9 mm jaws.

Spatulas/retractors/loops These instruments are essential for specific functions during intraocular surgery. They include the cyclodialysis spatula, iris and extraocular muscle hooks, and the lens loop. The cyclodialysis spatula is used bluntly to create a space between the sclera and the underlying iris and ciliary body for the treatment of glaucoma (Fig. 1.17). This instrument is about 120–140 mm long with a round to square serrated or knurled handle. Its tip is about 0.5–1.0 mm wide and 10–15 mm long with a blunt, rounded, or sharp end. This same design has also been incorporated into a cannula. This instrument can also be used to manipulate the iris, lens capsules, and vitreous. The iris hook is designed to retract the pupillary aspects of the iris. These hooks are about 120–140 mm long, and are constructed of either stainless steel or a nylon-like material (Delrin). These hook tips have a 1–3 mm curved end that is 1–4 mm wide and dull. Sharp or pointed iris hooks are not recommended as tearing of the dog and cat iris will usually cause hemorrhage. The muscle or strabismus hook is similar to the iris hooks, only the tip is much larger (Fig. 1.18). The instrument tip is angulated at 90 to facilitate placement under the extraocular muscles. These instruments are also used to rotate the globe. The lens loop is another vital instrument for lens and cataract removal in small animals. The lens loop is positioned to slide the cataract and lens material from the corneal or corneoscleral wound. With its handle shaped like the iris and muscle hooks, the lens loop’s tip is designed as a circularto-oval solid spoon or loop (Fig. 1.19). The overall size of these tips ranges from 0.3 to 6 mm wide and 7 to 15 mm long.

Fig. 1.17 Top: Two different cyclodialysis spatulas used for glaucoma and lens surgeries. The flat blade should be about 10 mm long and 1 mm wide, and has different angulations. Bottom: Cyclodialysis spatula combined with a cannula for injection into the anterior chamber.

Fig. 1.18 The strabismus or muscle hook is placed under the extraocular muscle to facilitate identification of the insertions as well as rotate the globe. Top: Von Graefe strabismus hook; bottom: Jameson muscle hook has a 6 mm hook with a 2 mm bulbous tip and a flat serrated handle. The tip may also be used for scleral depression during examination of the peripheral fundus.

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Surgical instrumentation

Fig. 1.19 The lens loop is used to facilitate sliding the lens from the eye. The loop may be different sizes and shapes. Top: New Orleans lens spoon has a 3 mm wide  14 mm long, slightly curved spoon on a 134 mm long flat serrated handle; bottom: Gills–Welsh modified lens loop with a 6  7 mm loop.

Cannulas for intraocular injections Special cannulas are necessary for corneal and intraocular surgery. With a reusable silicone bulb or anterior chamber irrigator and cannula, lactated Ringer’s or saline solution is occasionally sprayed on the corneal and conjunctival surfaces to provide essential moisture (Fig. 1.20). These cannulas range in size from 19 to 27 g. This same system is also used to re-inflate the anterior chamber with air or fluids once the corneal or limbal surgical wound has been apposed (Fig. 1.21). The cannulas may also be shaped as cyclodialysis spatulas, providing for two functions. Special cannulas to inject air or solutions have specially constructed ends, such as olive tips, side ports, and hooks. To inject the more viscid viscoelastic solutions, a slightly larger diameter cannula may be necessary.

Fig. 1.21 Ophthalmic cannulas may vary in diameter, length, shape, and purpose. Top: Air injection cannula (27 g); middle: Castroviejo cyclodialysis cannula (21 g); bottom: Bracken anterior chamber cannula. The latter two cannulas are used to inject solutions; for viscoelastics larger bore (18–19 g) needles are necessary.

Calipers During corneal, transscleral laser cyclophotocoagulation, cyclocryothermy, intraocular surgeries, intravitreal injections, and retinal detachment surgeries, distances between intraocular tissues and the exact size of tissues are very important. Several types of caliper are available that can be sterilized and should be part of the standard surgery instrument pack. These instruments permit measurements up to 20 mm in 1 mm or 0.5 mm increments. The Jameson and Castroviejo calipers are the most frequently used (Fig. 1.22). Fig. 1.22 Calipers for measurements during corneal and ocular surgeries. Top: Castroviejo; bottom: Jameson.

Rings

Fig. 1.20 Silicone bulb and cyclodialysis cannula to irrigate the anterior chamber with lactated Ringer’s solution, balanced salt solution or saline.

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Two types of ring are available for ophthalmic surgery; they include the external Flieringa and modified stainless steel single and double rings, and for intraocular use, the new capsular rings to insert within the capsular bag to expand the equatorial capsule. While the human elliptical cornea is about 7  8 mm in diameter, dog and cat corneas are considerably larger (dog: 16  15 mm; cat: 17  16 mm). Larger Flieringa rings, which are fortunately available, must be used; for dogs and cats the 20–22 mm diameter are recommended. Flieringa rings are attached around the cornea or limbus with four to six non-absorbable simple interrupted sutures to prevent globe and anterior chamber collapse as during keratoplasty. These rings are removed once the corneal wound has been apposed.

Surgical instruments for ophthalmic surgeries

Capsular tension rings have been introduced recently to expand the capsular bag after phacoemulsification and to facilitate insertion of an IOL. U-shaped, capsular tension rings are available in 12.5, 13.5 and 14.5 mm diameters for the dog.

Table 1.2 General surgical instruments for orbital surgeries

Instrument

Purpose

Allis tissue forceps

Hold and position tissues

Bard–Parker handle and blades

Incise the eyelids

Bishop–Harmon forceps, toothed

Grasp the conjunctiva and nictitans

Cannula: 19 g

Irrigation of the external eye

Enucleation scissors, large, curved

Incise the optic nerve

Eyelid speculum, wire

Retract the lids and maintain the palpebral fissure

Wet field or disposable cautery

Hemostasis

Jameson muscle hook

Manipulate the extraocular muscles

Metzenbaum scissors, medium

Incise and separate the orbital tissues

Mosquito forceps (2 curved, 2 straight)

Grasp tissues and for hemostasis

Needle holder, medium

Grasp and manipulate needle

Saline cup, small

Hold saline for moistening of tissues

Silicone bulb for irrigation

Irrigate the external eye

Tenotomy scissors, curved

Incise the conjunctiva and nictitans

Towel clamps (4 large, 4 small)

Maintain the surgical drapes

TM

Adaptations for large animals and special species ophthalmic surgeries As the veterinary ophthalmologist may be confronted with animal species that range in size from an elephant to a parakeet, surgical instrumentation is often determined by the size of the patient’s eye and sometimes available anesthesia. Fortunately, the elephant eye is similar in size to the horse, but for the parakeet even a 25 or 27 g needle is very large. For the larger animal species, the standard soft tissues surgical instruments are used for orbital and eyelid surgeries. For conjunctival grafts, corneal and intraocular surgeries, either the standard ophthalmic or microsurgical instruments are used. If the operating microscope is used, microsurgical ophthalmic instruments are recommended. Needle type and suture selection are identical for all species.

Surgical instruments for ophthalmic surgeries As ophthalmic surgeries are generally confined to certain ocular tissues, the development of specific surgical packs is recommended. Surgical packs are designed to limit the number of instruments anticipated for a surgery, and reduce the number of times an instrument requires cleansing, autoclaving, and non-surgical manipulations. Highly specialized ophthalmic instruments are best individually wrapped and sterilized, and used only when necessary.

Recommended instruments for orbital surgeries Although the majority of extraocular surgical procedures can be performed with general soft tissue instruments, the investment in ophthalmic surgical instruments will not only rapidly repay the surgeon the initial purchase costs, but also provide greater success rates for all patients. General soft tissue surgical instruments are used for most orbital surgical procedures and some of the more extensive eyelid surgeries (Table 1.2). Orbital surgery may also require some orthopedic instruments to transect and reappose the zygomatic arch in many animal species. Small Allis tissue forceps can be used to grasp and retract the orbital and eyelid tissues. The small Halsted mosquito forceps with straight and curved jaws are used for hemostasis by control of point bleeders, especially of the orbit, eyelids, and conjunctivas. The larger Kelly and Crile hemostatic forceps with either straight or curved jaws permit grasping of larger areas of tissue and are especially useful for orbital surgery. The curved Metzenbaum scissors, especially the smaller types, are indicated for most of the delicate orbital and eyelid tissue dissections. The Metzenbaum scissors should not be used to cut sutures. The heavy-duty Mayo dissecting scissors are useful for cutting the dense connective tissues of the orbit in large dogs.

Straight Mayo scissors, usually 6" (152 mm) long, are indicated for cutting sutures, especially sutures larger than 4-0. A good quality Mayo–Hegar needle holder is excellent for needles and suture sizes (4-0 to 2-0) that are used for the majority of orbital and eyelid surgical procedures. The Semkin and Adson tissue forceps may be used for orbital, eyelid, and conjunctival tissues, but the smaller ophthalmic fixation forceps may be less traumatic for these tissues. The Bard–ParkerTM scalpel handle, with the Nos 10 and 15 surgical blades, is used to incise orbital and eyelid tissues in small and large animals. The Beaver knife handle with several types of surgical blade (usually the Nos 6400 and 6500 microsurgical blades) is the most common knife for the ocular tissues of animals. A few general surgical instruments are usually part of any corneal or intraocular surgical instrument pack. At least four small (bulldog) towel clamps, and four larger towel clamps, small thumb forceps, small curved Metzenbaum scissors, and a small needle holder are used initially to improve exposure of the cornea and globe, and to perform the lateral canthotomy. The microsurgical instruments should not be used for the eyelids; these large tissues will eventually bend and disable these delicate instruments.

Recommended instruments for eyelid and conjunctival surgeries Although most eyelid, conjunctival, and nictitans surgeries can be performed with general surgical instrumentation, several instruments have been developed for specific lid surgical manipulations. As a result, a special eyelid surgery pack

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Table 1.3 Surgical instruments for eyelid surgeries

Instrument

Purpose

Towel forceps (4 large, 4 small)

Secure the drapes to the patient

Wire eyelid speculum (Barraquer)

Retract the lids and expose the conjunctiva/nictitans

Small curved Mayo scissors (Mayo/Metzenbaum)

Perform lateral canthotomy

Stainless steel cup

Hold saline/lactated Ringer’s solution for ocular irrigation

Silicone bulb and cannula

Periodically moisten the eye

Entropion/chalazion forceps

With an oval-to-round ring and solid base plate. Designed to clamp and stabilize the lid

Cilia forceps

Instrument

Purpose

Instruments for both surgeries Towel clamps (8)

Secure surgical drapes

Small curved Mayo scissors (Mayo/ Metzenbaum)

Lateral canthotomy

Stainless steel cup

Hold saline/lactated Ringer’s solution

Silicone bulb and cannula

Periodically moisten the eye

Wire lid speculum (adult/pediatric: Barraquer)

Retract eyelid/expose cornea

Small needle holder

Suture lateral canthotomy

With smooth tips designed to epilate the cilia

Tissue forceps: tooth/smooth (Adson)

Grasp conjunctiva/cornea

Bishop–Harmon forceps

Both serrated and 1  2 teeth tips. Good general tissue forceps

BeaverTM scalpel handle (Nos 6400 and 6500 microsurgical blades)

Incise cornea

Lid plate

Plastic or stainless steel. Holds the lids taut and protects the cornea from surgical manipulations

Tenotomy (Steven’s) scissors

Cut conjunctiva/sutures

Castroviejo needle holder

Use with 5-0 to 10-0 sutures

Use Beaver No. 6400 or 6700 microsurgical blade to incise eyelid skin/conjunctiva

For corneal surgeries

BeaverTM scalpel handle

Standard needle holder (Castroviejo/Barraquer)

Tenotomy scissors (Steven’s) curved/straight

Corneal section scissors (right/left pair)

Cut cornea/limbus/sclera

Standard size recommended to accommodate the larger needles and suture sizes. Some prefer holders with a lock device

Martinez or Gill dissector

Bluntly separate corneal stromal layers

Calipers

Operative measurements

Two different sizes recommended. Blunt tips preferred

Cyclodialysis spatula

Manipulate iris, lens, vitreous

Disposable ophthalmic cautery

Hemostasis/cut iris

Corneal trephines (5–9 mm)

For keratoplasty

Microsurgery needle holder

For keratoplasty

may be utilized using the standard size ophthalmic surgical instruments (Table 1.3).

Recommended instruments for corneal surgeries For corneal and intraocular surgery in small animals, a number of instruments are essential. Often, a combination of the standard and microsurgical ophthalmic instruments is included in a standard surgical pack. The corneal instrument pack should have a limited number of instruments. Additional infrequent use but essential ophthalmic instruments are individually packaged and sterilized, and can be used as needed. As the basic pack instruments are repeatedly cleaned and sterilized, these instruments can be subjected to considerable wear. A list of surgical instruments for a typical corneal surgical pack is summarized in Table 1.4. These instruments accommodate all of the surgical procedures, except for partial and full-thickness corneal grafts (keratoplasty), including bulbar and palpebral conjunctival grafts, corneoconjunctival and corneoscleral transpositions, superficial and deeper keratectomies, partial and full-thickness corneal lacerations, removal of partial and full-thickness corneal foreign bodies,

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Table 1.4 Surgical instruments for conjunctival and corneal surgeries

and limbal surgeries. The instrumentation for corneal grafts is not extensive but very specific. Because dog and cat corneas are very tough, corneal scissors and trephines must be very sharp.

Recommended instruments for intraocular surgeries and cataract extractions The instrumentation to perform all iris–ciliary body, glaucoma, cataract, and lens removal surgical procedures is summarized in Table 1.5. More instruments are necessary for lens and cataract surgeries than for glaucoma and anterior uveal surgical procedures. The selection of these instruments should serve only as a guide; individual preferences for specific instruments, based on shape and size, vary.

Instruments for vitreoretinal surgeries Current training of veterinary ophthalmologists is similar to human ophthalmology, and provides broad exposure to animal eye diseases and surgery in all animal species during

Instrument care, storage, and sterilization

Table 1.5 Surgical instruments for intraocular surgery in animals

Box 1.1

Recommended instruments and materials for vitreoretinal surgeries*

Instrument

Purpose

Towel clamps (4 large, 4 small)

Secure surgical drapes

General

Small curved Mayo scissors

Lateral canthotomy

• •

Saline cup

Hold saline/lactated Ringer’s solution

Silicone bulb and cannula (cannula: 19 g/25 g)

Periodically moisten the eye

Eyelid speculum (adult/pediatric)

Retract eyelid/expose cornea

Small needle holder

Suture lateral canthotomy

Tissue forceps: toothed/smooth (Adson)

Grasp conjunctiva/cornea

Tying forceps with teeth

Grasp cornea/sutures

Instruments

Beaver scalpel handles (Nos 6400, 6500, and 6700 microsurgical blades and keratome)

Incise cornea/limbus/sclera

Tenotomy scissors (Steven’s)

Cut conjunctiva

Utility scissors (Steven’s tenotomy)

Cut sutures

Corneoscleral scissors (right/left pair)

Incise cornea/limbus/sclera

Iris scissors

Incise iris

Extracapsular lens forceps

Grasp anterior lens capsule

Capsulectomy forceps (Utrata) (capsulorhexis)

Tear/remove anterior lens capsule

• • • • • • • • • • •

Lens loop

Slide lens from eye

Cyclodialysis spatula

Separate tissues

Muscle hook (Jameson)

Rotate globe/cataract surgery

Needle holder (standard/microsurgery)

Suturing

Other Calipers

Operative measurements

Disposable cautery (sterile)

Hemostasis/cut iris

Intraocular forceps

Grasp/remove lens capsule/ fragments

Intraocular scissors

Cut anterior lens capsule

Vannas capsulotomy scissors

Cut anterior lens capsule

Intraocular lens forceps/hook

Position or dial intraocular lens

a 3-year residency. Further specialization in human ophthalmology (often termed fellowships) occurs following their residencies, and provides physicians with in-depth training in, for instance, cornea, glaucoma, retina, and neuro-ophthalmology. Clinical fellowships have yet not developed in veterinary ophthalmology, but could focus on either specific ocular areas or even species. Vitreoretinal surgeries require additional training for veterinary ophthalmologists, and most performing this type of surgery have been trained in medical schools. With a limited number of veterinary vitreoretinal surgeons available, this type of surgery represents a new and exciting frontier for veterinary ophthalmology. For vitreoretinal surgeries, highly

•

Good quality operating microscope. Viewing system for the posterior segment: Machemer irrigating lens, other sew-on ring sets, or non-contact BIOM system. A more expensive wide-angle system is available. Both systems can be used in dogs. These systems use indirect ophthalmoscope principles (which invert the ocular fundus appearance) and may require an inverter for use. Vitrectomy system with light-illuminating sources, electrocautery, and air infusion. Newer units may also have ultrasonic fragmentation and silicone oil pumps. The vitrectomy unit is usually a guillotine-type cutter on the side of a 20 g blunt tube.

Microvitreoretinal (MVR) blades (20 g) High-viscosity infusion tubes (4 mm cannula) Scleral plugs and plug holder Light pipes Electrocautery sets Vitreous scissors and forceps Silicone-tipped 20 g needles Charles (fluted) needle and handle Laser endocoagulation system PFCLs (perfluorocarbons) Silicone oil (1000–5000 cSt)

*Recommended by Vainisi SJ, Wolfer JC 2004 Veterinary Ophthalmology 7:291–306. For more information, see Chapter 12.

specialized instruments are necessary, and are expensive (Box 1.1). Additional information on these instruments and their use is available in Chapter 12.

Instrument care, storage, and sterilization The investment in a complete and high-quality set of corneal and intraocular instruments can be considerable. These instruments, if carefully used, cleaned and stored, can last a very long time. Special instrument trays are available for both sterilized instruments ready for use or for long-term storage as non-sterile instruments. All of these instruments should be maintained in individual compartments within these trays and not allowed to contact each other. The delicate tips of these instruments should be covered and protected with old rubber or plastic tubing. For cleaning, the ultrasound cleaner provides the safest and most thorough method to remove all blood, tears, and other salt-containing residues. The ophthalmic instruments should be individually placed in and removed from the ultrasound unit to avoid any damage. Jostling these instruments together will potentially cause irreversible damage and bend the tips and dull the cutting edges. After thorough cleaning, the instruments should be air dried. Both steam and ethylene gas are used for ophthalmic instrument sterilization. The flash steam cycle may gradually dull the cutting instruments’ edges.

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Table 1.6 Characteristics of sutures for animal ophthalmic surgery

Suture type

Suture size

Ocular tissues

Nylon (monofilament)

5-0 to 12-0

Eyelid skin, cornea, sclera

Silk (braided)

5-0 to 7-0

Eyelid skin, conjunctiva, cornea, limbus

Polyester

5-0 to 7-0

Eyelid skin, limbus

Polypropylene

5-0 to 10-0

Eyelid skin, cornea

Chromic catgut

2-0 to 4-0

Subcutaneous tissues, subconjunctival tissues, fascial layers

Polyglactin 910 (braided and monofilament)

5-0 to 8-0

Subconjunctival tissues, cornea, sclera, limbus

Polyglycolic acid

5-0 to 7-0

Subcutaneous tissues, subconjunctival tissues, cornea, sclera, limbus

Polydioxanone

5-0 to 7-0

Subcutaneous tissues, subconjunctival tissues, cornea, sclera, limbus

Non-absorbable

Absorbable

Ophthalmic sutures and needles The general rule stating that the strength of the suture should approximate the surrounding tissues also pertains to ophthalmic sutures. For surgery of the orbit, suture size approximates that of general soft tissue surgery, with 2-0 to 5-0 absorbable sutures used for ligation and closure of the deeper orbital fascial tissues. Skin closure is usually with non-absorbable 3-0 to 5-0 nylon, polypropylene, polyester, Dacron, or silk. For surgery of the eyelids, 3-0 to 5-0 sutures are recommended, with the absorbable sutures buried and the skin apposed with non-absorbable 3-0 to 5-0 single interrupted sutures. Most conjunctival and corneal sutures are absorbable (to eliminate the need for suture removal), and 5-0 to 8-0 in size to minimize tissue reaction. The different ophthalmic sutures and their characteristics are listed in Table 1.6. Often the choice of the skin sutures is personal preference and nearly always the non-absorbable type. However, in some exotic small animals, skin suture removal may be impractical because of restraint, and absorbable subcutaneous or skin sutures are employed. Silk skin sutures are usually black, soft and pliable; if suture contact with the eye occurs, significant ocular irritation is unlikely. Unfortunately, silk sutures are braided and bacteria can penetrate the sutures, hence suture removal should be performed 10–14 days postoperatively. When nylon and polypropylene monofilament are employed for skin sutures, surgeon and square knots are usually combined to secure

each knot. As these sutures are fairly stiff, suture contact with the conjunctiva and/or cornea usually induces ocular irritation. This stiffness can be used to advantage during parotid duct transposition when these sutures are inserted with a flamed or blunted end into the duct’s lumen to facilitate detection and handling. The Dacron polyester suture is more pliable than the nylon or polypropylene, but its knots tend to loosen. Buried sutures involving the nictitating membrane may be either absorbable or non-absorbable depending on the procedure. Absorbable sutures are most frequently used for the deeper layers of the eyelids, all layers of the conjunctiva and nictitating membrane, and the cornea. Our preference is polyglactin (VicrylW; Ethicon, Somerville, NJ), a multifilamentous suture, with strength and resorption rates that approximate surgical gut (about 6 weeks). This suture, dyed violet, is non-antigenic and produces minimal tissue reaction. Uncoated polyglactin is associated with excessive tissue drag during suturing; coating greatly reduces this drag but additional ties are indicated for knot security. Polyglactin sutures are stable in septic wounds, and can be used in infected corneas. In general, reverse cutting semicircular needles are recommended for the majority of extraocular surgical procedures. Skin closure generally employs conventional cutting needles; the subcutaneous and deeper orbital fascial layers are apposed using spatula and taper needles. Corneal and scleral tissues require reverse cutting needles, and the G-6 semicircular needle is the most useful.

Further reading Boothe HW: Suture materials, tissue adhesives, staplers, and ligating clips. In Slatter D, editor: Textbook of Small Animal Surgery, ed 3, vol 1, Philadelphia, 2003, WB Saunders, pp 235–243. Gelatt KN, Gelatt JP: Handbook of Small Animal Ophthalmic Surgery. Vol 1: Extraocular Procedures, Oxford, 1994, Pergamon Press, pp 1–10.

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Gelatt KN, Gelatt JP: Handbook of Small Animal Ophthalmic Surgery. Vol 2: Corneal and Intraocular Procedures, Oxford, 1995, Pergamon Press, pp 1–14. Gelatt KN, Gelatt JP: Small Animal Ophthalmic Surgery, Oxford, 2001, ButterworthHeinemann, pp 1–16. Grevan VL: Ophthalmic instrumentation, Vet Clin North Am Small Anim Pract 27:963–986, 1997.

Kohn R: Textbook of Ophthalmic Plastic and Reconstructive Surgery, Philadelphia, 1988, Lea and Febiger, pp 2–55. Merkley DF, Wagner SD: Surgical instruments. In Bojrab MJ, editor: Current Techniques in Small Animal Surgery, ed 3, Philadelphia, 1990, Lea and Febiger, pp 3–33. Nasisse MP: Principles of microsurgery, Vet Clin North Am Small Anim Pract 27:98–1010, 1997.

Further reading Smeak DD: Selection and use of currently available suture material. In Bojrab MJ, editor: Current Techniques in Small Animal Surgery, ed 3, Philadelphia, 1990, Lea and Febiger, pp 34–39. Stades FC, Gelatt KN: Diseases and surgery of the canine eyelids. In Gelatt KN, editor:

Veterinary Ophthalmology, ed 4, vol 2, Ames, 2007, Blackwell, pp 563–617. Troutman RC: Microsurgery of the Anterior Segment of the Eye, St Louis, 1974, CV Mosby, pp 96–115.

Warren C: Phaco chop technique for cataract surgery in the dog, Vet Ophthalmol 7:348–351, 2004. Wilkie DA, Colitz CMH: Surgery of the canine lens. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, vol 2, Ames, 2007, Blackwell, pp 888–931.

15

CHAPTER

2

The operating room Kirk N. Gelatt

Chapter contents Introduction

17

Electroepilation

26

Magnification

18

Cryotherapy

26

Illumination

20

Laser therapy

27

Chairs for microsurgery

20

Perioperative drugs

30

Patient preparation

21

Patient recovery/restraint

31

Basic operative approach

22

Subpalpebral medication systems

32

Hemostasis

25

Introduction The operating room for extraocular surgeries is usually the standard operating room with more specialized illumination. Limited magnification, provided by head loupes and spectacle-mounted telescopes, is usually sufficient for surgeries of the orbit, eyelids, nasolacrimal system, nictitating membrane and conjunctiva. However, in the operating room where corneal and intraocular surgeries are routinely performed, in addition to the operating microscope, special instruments often include the phacoemulsification unit, ophthalmic cautery, cryotherapy, laser instrumentation, and retinal detachment surgery instrumentation. Depending on the number and type of ophthalmic surgical procedures performed daily or weekly, the composition of the operating environment will vary. The operating microscope is the largest single investment, but will last for a very long time with proper care. To the full-time veterinary ophthalmologist, the operating microscope is indispensable for corneal and intraocular surgeries in all animal species. A cabinet is maintained within the operating room for ophthalmic surgery, with special sterile instruments, individually wrapped, and ready for use. I prefer limited numbers of ophthalmic instruments arranged as external, minor, and major intraocular surgical packs. Another method divides the eye instrument packs based on intended use. Additional special instruments, individually wrapped and sterile, can be opened when needed; this reduces the wear and tear of cleaning and sterilization on instruments used infrequently but vital for certain eye surgeries. The external

eye surgical pack is used to drape the surgical area, expose the globe, perform the lateral canthotomy, and appose the surgical wound. The external eye instrument pack should contain small towel clamps, a small saline bowl, a silicone irrigator for solutions to keep the cornea and conjunctiva moist, a few small hemostats, ophthalmic tissue forceps, strabismus, utility or tenotomy scissors for ocular tissues and sutures, small serrated and 1  2 teeth thumb forceps, knife handle and blades, and one or more eyelid specula. The minor intraocular surgical pack provides the essential surgical instruments for corneal, glaucoma, and iris– ciliary body surgeries. The instruments in this pack can also be used to perform conjunctival grafts, superficial keratectomies, and primary closure of corneal ulcerations, and to treat partial to full-thickness corneal lacerations with an iris prolapse. This pack contains exclusively ophthalmic instruments, with small serrated, 1  2 teeth and tying forceps, curved and straight ocular scissors, cyclodialysis spatula, standard and micro-ophthalmic needle holder, corneal and anterior chamber irrigator, and portable batterypowered cautery unit. Special ophthalmic instruments, such as a corneal separator and iris scissors individually wrapped, sterile and ready for use, should be available within the operating room. The major intraocular surgical packs provide the instrumentation for cataract and lens removal, and posterior segment diseases (mainly vitreous). The instruments in this pack include corneal section (cataract or corneoscleral) scissors, different types of tissue and tying forceps, the lens loop and spoon, cyclodialysis spatula, cautery unit, two or more

2

The operating room

cannulas, extracapsular lens forceps, forceps for tearing of the anterior lens capsule (capsulorhexis), and one or two different size needle holders. Other instruments, individually wrapped and sterile, should include iris scissors, intraocular scissors, and intraocular forceps. Some backup instruments should be available in case contamination or malfunction of instruments occurs during the surgical procedure. Tables 1.2–1.5 and Box 1.1 list the different instruments for the varying ophthalmic surgeries. For more specialized surgeries, such as retinal detachment surgeries (see Table 1.5), instruments are often wrapped and sterilized separately.

Magnification For nearly 40 years veterinary ophthalmic surgery has been progressively refined, and microsurgical procedures performed under the operating microscope, that started in the early 1980s, are now commonplace for surgery of the cornea and intraocular structures. Microsurgery for human ophthalmology started slowly in the 1950s by Perrit. The first commercial operating microscope was produced by Zeiss and featured coaxial illumination. Important refinements by Barraquer (XY mechanism) and Troutman (motorized zoom) defined the basic components of the modern operating microscope. The development of microsurgical instruments, sutures, and needles also stimulated the concurrent requirement for magnification. Surgical procedures of the extraocular tissues including the orbit, eyelids, nasolacrimal, and tear systems are still traditionally non-microsurgical; however, microsurgery involving the conjunctiva, cornea, and intraocular tissues has become common because of the small ophthalmic needles and sutures, and the need for exact apposition of the involved tissues. Initial use of the operating microscope may be somewhat frustrating and may prolong the surgical procedure. However, with patience and practice, the veterinarian will quickly appreciate the advantages of corneal and intraocular surgeries performed under magnification.

Head-mounted magnifiers The exact requirements for magnification vary and are often influenced by the surgical patient load and the different types of ophthalmic surgical procedure performed. The simplest and least expensive magnification device is the binocular magnifier loupe worn on the head (Fig. 2.1). These head loupes can be used over prescription glasses. The head loupe is available in a number of different magnifications. Generally the lower magnifications are the most versatile because at the higher magnifications the focal length of the loupe is reduced, thereby limiting the working distance between the surgeon and the operating field. For instance, the head loupe with the 1.5 magnification has a focal length of 51 cm; the 1.75 magnification has a focal length of 35.5 cm; the 2 magnification is in focus at 25.5 cm; and the 2.5 magnification has a focal length of 20.5 cm. Individual telescope magnifiers are another low-cost alternative, and are generally recommended. They can be added to head loupes or attached directly to spectacles.

18

Fig. 2.1 Binocular magnifier loupe.

These units permit accommodation for different interpupillary distances, allow use of prescription glasses, and can be elevated when not in use (Fig. 2.2). Although these units are lightweight, use for several hours when attached to spectacles can be very tiring.

Operating microscopes Most veterinarians interested in corneal, intraocular, and vitreoretinal surgeries will eventually invest in an operating microscope. Once proficiency is achieved using the operating microscope, corneal and intraocular surgeries can be performed easily and quickly. The microsurgical ophthalmic instruments and very small 7-0 to 12-0 sutures can be easily manipulated with some magnification. The microscopic details provided during corneal incisions and wound apposition enhance the possibility of successful surgeries. Operating microscopes can be portable and attached to either a table or floor base with casters. Table units are the least expensive, usually provide observation for only the surgeon, and changes in focus require manual adjustments (Fig. 2.3). Stationary ceiling-mounted operating microscopes are used infrequently in veterinary ophthalmology because of the need for portability between operating

Fig. 2.2 Telescope magnifier loupe.

Magnification

Support arm to floor or ceiling mount

Assistant surgeon

Primary surgeon

Observer tube for video or 35 mm camera

Base microscope with built-in light system

Fig. 2.3 Portable table-mounted operating microscope. Unit weighs 9 kg and can be clamped to the surgery table. Working distance is 20 cm.

rooms. Most veterinarians use the floor-based operating microscopes which are very stable but mobile (Fig. 2.4). The operating microscope has several standard parts (Fig. 2.5). The base and mount are usually quite heavy and vary depending on whether the unit is table, floor or ceiling mounted. Various supporting arms permit adjustment of the operating microscope’s main body over the patient’s eye and angulation of the scope to the surgical field. With a large footplate that contains several switches, the surgeon can raise and lower the main body of the operating microscope to permit motorized coarse and fine focus of the surgical field. The scope’s main body consists of the focus and zoom systems, and a beam splitter that permits observation of the surgical field by the surgeon and assistant surgeon, and often a video recorder or 35 mm or digital camera. The fine focus of the surgical field and zoom or magnifying system

Fig. 2.5 Standard components of the operating microscope for ophthalmic microsurgery.

are also controlled by a foot pedal. This allows slight adjustments on magnification and/or focus without interrupting surgery. As with the head-mounted magnifiers, the magnification of the operating field is variable and inversely related to the focal length. The range of working distance between the patient’s eye and the base of most operating microscopes is 125–500 mm, with 200–250 mm the most common distance. The larger microscopes provide for dual observations for the surgeon and an assistant, and often an additional observer or camera (35 mm or digital SLR cameras or video recorder). Adjustments in magnification (zoom) and focal length are usually achieved by foot controls that change the focus up and down, and change the magnification (zoom). Magnifications with these operating microscopes vary, but generally range from 3 to 15 or 20. Most Fig. 2.4 Floor-based operating microscope. Unit provides for viewing by the surgeon, assistant surgeon, video recorder, TV and digital camera.

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The operating room

scopes have built-in zoom systems that permit immediate changes in magnification during surgery. Other models have different fixed steps of magnifications that require manual changes. With the operating microscopes with different fixed magnifications, parfocalization is important to avoid marked variations in focus during changes in magnification. To accommodate changes in both magnification and focus, the center of the surgical field should be in the middle of the microscope’s field, and the surgical area should be relatively level. Hence, the animal eye is carefully positioned so that the entire cornea, anterior chamber and iris surface are at the same levels of focus. Resolution of surgical field is optimal in the center of the scope’s optical system. Changes in the amount of magnification directly influence the size of the surgical field. With the 12.5 eyepiece, the 125 mm objective provides a surgical view of about 20 mm diameter; with the 200 mm objective the surgical view is 33 mm diameter; with the 300 mm objective, the surgical view is 50 mm diameter; and with the 500 mm objective, the surgical view is about 80 mm diameter. The most comfortable magnification and working distance is generally in the 175 range. Although higher magnifications may provide additional details, they reduce the working space as well as the depth of field. The magnification also influences the depth of the surgical field; as magnification increases, the depth of the field decreases. During cataract surgery in the dog or cat, some change in the operating microscope focus should be anticipated. Initially at least one area of focus is the cornea and the incision into the anterior chamber, and later a second area of focus is the anterior lens for tearing and removal of the anterior lens capsule. The magnification may need to be changed further to permit visualization of the posterior lens capsule. I recommend the lower range of magnification for the surgeon initially which accommodates longer working distances between the operating microscope and the patient’s eye, and greater depth of the surgical field for most corneal and intraocular surgeries. This usually permits visualization of the entire eye and the palpebral fissure. With experience, the higher magnification or the zoom feature of the microscope can be used, but generally with the surgical field no smaller than the cornea. Some operating microscopes possess sterile caps for both the objectives (to permit small adjustments in the interpupillary distances and the focus of each objective) and the base of the microscope (however, as a general rule, if the surgical instrument touches anything except the patient’s eye and draped instrument table, it is discarded and a new instrument substituted). Illumination systems are usually of two types: 1) the primary light system is incorporated into the operating microscope permitting direct illumination of the eye that is especially helpful during surgery in the posterior chamber and in the vitreous space; and 2) an ancillary light system mounted next to the operating microscope body that directs light to the eye at a slight angle. These light systems also function as a reserve; if one bulb malfunctions, the surgical field will continue to be illuminated. Both systems should have heat-absorbing filters to shield the eye as much as possible. Often the main and accessory light systems possess rheostats, permitting independent changes in the intensity of illumination. Retinal phototoxicity may occur with

20

prolonged and intense illumination of the ocular fundus. The minimum level of illumination to adequately perform the surgery is the best guide. Because of the magnification, positioning of the eye for surgery is important. With 10 to 20 magnification the depth of field is limited. As a result, the dog or cat is placed in dorsal recumbency, the head is stabilized by a U-shaped vacuum pillow or sandbags, and the operated eye is positioned in the center of the operating microscope’s field, with the cornea, anterior chamber, iris, and lens surfaces within focus. Other species, for instance the horse, are placed in lateral recumbency, and vacuum pillows or sandbags are used to position the head so that the eye is parallel to the operating microscope and the different areas of the cornea are in the same focus. If the eye is not level with the operating microscope, surgery in different places on the cornea or elsewhere will require intermittent changes in focus throughout the entire surgery. To simplify the optics of the operating microscope, maintaining both the scope and the patient in a vertical plane (rather than at an angle) will permit the majority, if not all, of the surgical field to remain in simultaneous focus.

Illumination Adequate illumination is essential for ophthalmic surgery. The dark ocular tissues, especially the anterior uvea, require high intensity focal illumination for visibility. Traditional sources of light for ophthalmic surgery include overhead surgical lamps, primarily for extraocular surgical procedures; portable and ceiling-mounted ’cool lamps’ that filter the majority of infrared light waves that dry the tissues, used for both extraocular and intraocular surgical procedures; and direct and fiberoptic light systems that are routed through the operating microscope during microsurgery. Small focal operating and examining lamps that are head mounted may also be considered; however, because of their weight, they are generally used for only short periods of time. Many different models of each illumination system are available; choice of the surgical lamp is also influenced by the anticipated frequency of use and costs. As a general rule, once the ocular tissues are illuminated during ophthalmic surgery, intermittent irrigation of the corneal and conjunctival surfaces with sterile 0.9% saline or balanced salt solution should be performed to prevent corneal and conjunctival epithelial damage.

Chairs for microsurgery All corneal and intraocular surgical procedures in small animals are performed with the surgeon and assistant surgeon seated on adjustable stools with casters (Fig. 2.6). The height of the stools should be adjustable to accommodate different surgeons as well as the height of the operating table and the patient. The recommended operating room chairs can be adjusted with a hydraulic activated foot pedal, permitting changes during surgery without interrupting surgery. In some stools the back rest can be rotated 180 and moved to the front of the surgeon to provide arm rests during microsurgery. These arm rests can be covered with sterile

Patient preparation

purpose. The contact lens is removed immediately before surgery along with any hair and debris from surgical preparation.

Cleansing and disinfection

Fig. 2.6 Adjustable stool for ophthalmic surgery. Stool height is adjusted by the foot-operated hydraulic control, and the back rest can be rotated for use as an arm support.

stockinet. The operating chairs for the surgeon and assistant surgeon should be comfortable and help to avoid fatigue that can adversely impact surgery.

Patient preparation Preparation of the skin of the eyelids and conjunctiva differs from that of most other general surgical procedures. During cleansing and preparation of the eyelid skin, these agents often contact the cornea and conjunctiva. As a result, solutions such as iodine in alcohol (Lugol’s solution) and isopropyl alcohol routinely used for skin preparation in general surgery are avoided as they are very toxic to the corneal and conjunctival epithelia, and cause immediate epithelial sloughing.

Clipping of hair and eye protection The hair and eyelashes are carefully clipped with small electric hair clippers. The eyelashes may be coated with petroleum jelly or ophthalmic ointment, and carefully clipped by small sharp scissors. While removing the hair of the eyelids and adjacent skin about the orbit, one should avoid creating any nicks and abrasions as these wounds can cause unnecessary irritation and unsightly swellings postoperatively. Several different strategies have evolved to protect the eye during surgical preparation of the eyelids and/or conjunctiva. Liberal amounts of ophthalmic ointment or petroleum jelly can be applied to the cornea just before clipping the eyelid hair. Hairs that fall onto the cornea and conjunctiva become embedded in the petroleum jelly, which is carefully removed later with sterile cotton swabs. A reusable plastic contact lens coated with ointment can also be used for this

The eyelids and adjacent orbital skin are cleaned and prepared for corneal and intraocular surgery. A mild antiseptic solution containing aqueous 0.5% povidone–iodine is the recommended ocular surface disinfectant for all ophthalmic surgical procedures. Chlorhexidine diacetate (0.05% and 0.5%) is toxic to the canine eye and causes chemosis, corneal epithelial edema, and corneal erosions. However, chlorhexidine gluconate (0.05%) with 4% isopropyl alcohol is both a safe and effective antimicrobial disinfectant for the dog’s cornea and conjunctiva. Both povidone–iodine and chlorhexidine are bactericidal. The 0.5% aqueous dilution of povidone–iodine produces rapid broad-spectrum antimicrobial effects against the commonly isolated Staphylococcus aureus, Staphylococcus epidermidis, a-hemolytic Streptococcus sp., and Escherichia coli, as well as many fungi and viruses in the dog. At effective antimicrobial dilutions, such as the 0.5% level, povidone– iodine does not cause corneal epithelial edema, corneal epithelial sloughing, eyelid edema, or conjunctival irritation in the dog. After at least two 1-minute cleansing periods with povidone–iodine, the eyelids, conjunctiva, and cornea are liberally flushed with sterile 0.9% saline or balanced salt solution. Sterile cotton-tipped swabs are used to remove any remaining exudates and hair from the conjunctival fornices and surfaces, and the ophthalmic surgical site is ready for draping. The 5% povidone surgical scrub, which contains 4.5% alcohol, provides an excellent germicidal preparation of the facial skin (as for parotid duct transposition), but cannot safely be used for the eyelids. This preparation is toxic to the corneal epithelium, producing a generalized loss of this layer (essentially a chemical superficial keratectomy). Most corneal and intraocular surgeries are performed with the pre-existing ophthalmic condition requiring medication within the operating room. Accordingly, the eye is often medicated immediately preoperatively, during the operative procedure, and following surgery. Often the preoperative condition or the immediate postoperative inflammation can be substantially reduced as a result of this perioperative medication of the eye and adjacent structures. Recent studies in dogs indicate that bacterial contamination of the anterior chamber occurs in about 30% of dogs undergoing cataract surgery, and topical as well as systemic antibiotics should be administered. Antibiotic therapy for full-thickness corneal perforations and lacerations is often administered during the surgical correction in the solutions used to irrigate the external ocular surfaces, and for re-establishment of the anterior chamber after repair of the corneal defect. Fortunately, bacterial endophthalmitis is very rare in the dog after intraocular surgery.

Head positioning The majority of corneal and intraocular surgical procedures are performed with the small animal patient in dorsal recumbency. If head-mounted magnifiers are worn, the

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The operating room

Irrigation To prevent drying of the conjunctival and corneal surfaces during ophthalmic surgery, small volumes of sterile 0.9% saline, balanced salt solution, lactated Ringer’s solution, or other physiologic solutions are used intermittently to moisten the ocular tissues. Both the pH and tonicity of these solutions should approximate the tear and aqueous humor fluids. Inadequate levels of moisture provided during eye surgery will result in unnecessary corneal epithelial damage and possible limitations on the use of certain classes of medications postoperatively.

Sponges/swabs Fig. 2.7 Vacuum U-shaped pack for ophthalmic surgery.

dog may be positioned in lateral recumbency. Ropes and adhesive tape are used to position the animal’s legs. Although the duration of most ophthalmic surgical procedures is less than 1 h, a circulating water heating pad between the patient and the surgery table reduces the possibility of hypothermia. It is important to place the animal’s head in a secure position to prevent any positional changes during surgery. Towels, water bottles, or several small lowcost sandbags can be used to maintain the head in the desired position. An alternative superior scheme uses a vacuum bead-filled U-shaped pack for stabilizing the head (Fig. 2.7). The patient’s head is positioned on the vacuum pack, and the pack is manipulated to provide the selected head position. Once the proper position is achieved, vacuum is applied temporarily to the pack. Once the air is removed, the pack becomes very rigid, holding the head in a fixed position. Release of the vacuum postoperatively causes the pack to return to a soft and moldable structure.

To assist with hemostasis and removal of material during ophthalmic surgery, small sterile cotton swabs are used routinely for corneal surgeries, and for the extraocular aspects of intraocular surgeries. For use inside the anterior chamber during intraocular procedures and full-thickness corneal surgical procedures, disposable cellulose sponges (often triangular shaped) are recommended. Cotton swabs are avoided during intraocular surgical procedures because some of the small cotton fibers may loosen and enter the anterior chamber, increasing the intensity of postoperative anterior uveitis.

Basic operative approach For corneal and intraocular surgeries, exposure of the entire cornea and anterior segment is preferred. In most small animals under general anesthesia, the globe rotates downward and inward. This may be advantageous for corneal and anterior segment surgeries involving the dorsal and dorsolateral regions, but not when access and visibility of the entire cornea and anterior segment are necessary. With less than adequate surgical exposure, the duration of surgery is prolonged and the procedure may be more difficult to perform.

Draping Once surgical preparation of the eye and associated structures is complete, the area is carefully draped for surgery. Simultaneous use of both paper (barrier) and reusable cloth (to absorb any moisture) drapes is recommended. Plastic drapes with self-adherent backings and rubber dental dam material can also be employed immediately about the surgical site. Cloth drapes are used to absorb the irrigation solutions, but unfortunately allow contamination with the other non-sterile surfaces of both patient and operating table. Paper or barrier drapes repel all moisture and prevent contamination from the other areas, and are most often used. Our standard draping procedure is to position four small surgical towels about the surgical site to absorb the irrigation solutions, and secure them with small bulldog towel clamps. An additional large paper drape with a small hole to provide adequate surgical exposure is placed over these towels and secured with additional towel clamps. As with any surgical procedure, draping is designed to provide adequate exposure of only the operative site and a barrier to the adjacent non-sterile areas.

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Retrobulbar injections in dogs Access to the cornea and anterior globe may present exposure problems in small animals, especially in certain breeds of dog. Fortunately, the lateral and dorsolateral aspects of the dog orbit are incomplete, and accommodate retrobulbar injections. Injections of sterile 0.9% saline can enhance the presentation of the cornea and globe, but only with some risk. The injection is performed with the dog under general anesthesia with the objective of forcing the globe further rostrad or forward in the orbit, or to turn the globe and improve exposure of a selected area of the cornea and/or anterior segment. The amount of sterile saline injected is ascertained as the injection is performed and the response of the globe to the space-occupying solution. The hypodermic needle may be inserted caudal to the junction of the lateral orbital ligament and dorsal aspects of the zygomatic arch (Fig. 2.8). The needle is directed towards the retrobulbar space in a ventromedial direction toward the opposite

Basic operative approach

Fig. 2.8 An 8 cm, 22 g hypodermic needle is inserted dorsal to the zygomatic arch and caudal to the lateral orbital ligament, and directed toward the opposite mandibular joint in the dog. A variable volume of sterile saline can be injected in the animal under general anesthesia to force the globe forward.

mandibular joint. The solution may be injected in the lateral aspects of the extraocular muscle cone, or immediately caudal to the globe and within the retrobulbar muscle mass. Injections external to the retrobulbar muscle cone will rotate the globe laterally; injections immediately behind the globe will push the globe forward. The volume injected should be limited to produce the desired outcome but not result in undue pressure and distortion of the globe. Another injection site is ventral to the anterior zygomatic arch and rostrad to the vertical portion of the ramus of the mandible (see Chapter 3). The hypodermic needle, after passing the ramus of the mandible, is directed toward the orbital fissure. Injections external to the retrobulbar muscle cone in the orbital floor and the medial orbit wall are possible with this method, and can be used to shift the globe dorsally. Retrobulbar injections can also be performed with curved hypodermic needles directed through the conjunctiva or the eyelids to deposit solution beside or caudal to the globe. The volume and position of the injection within the orbit will shift the eye accordingly. With the use of neuromuscular paralyzing drugs, retrobulbar injections are generally not necessary.

Retrobulbar injections in cats Retrobulbar injections in the cat are not recommended because of the limited retrobulbar space and difficulty in proper positioning of the injection.

Retrobulbar injections in horses Retrobulbar local anesthetic injections have been described in the horse by Berge and Lichenstern. The posterior orbit and entry of the critical cranial nerves in the horse is about as deep as in cattle, but the posterior orbit is more conical.

With gas inhalation general anesthesia and often neuromuscular blocking agents and forced ventilation, retrobulbar nerve blocks in the horse are infrequent. In the Berge method, an 8–10 cm, 18 g needle is inserted caudal to the supraorbital process of the frontal bone near the supraorbital foramen. The long needle is directed ventromedial (about 40 from the vertical) and slightly caudal toward the area of the orbital fissure where 15–20 mL of local anesthetic is injected (see Chapter 3). In Lichenstern’s method, an 8–10 cm, 18 g needle is inserted 1.5 cm caudal to the middle of the supraorbital process. The needle is directed toward the opposite last upper premolar tooth. The taut extraocular muscles’ fascial cone may be felt as the needle penetrates it. Approximately 20 mL of local anesthetic is injected near the orbital fissure (see Chapter 3). As a third method, the lateral and medial canthal routes may be used to inject about 10–15 mL of local anesthetic at each site. Of the large animal species, intraocular surgery is performed most often in the horse. As this species has considerable scleral elasticity (low scleral rigidity), sizeable retrobulbar injections can markedly indent the posterior segment and increase the likelihood of vitreous prolapse during cataract surgery.

Retrobulbar injections in cattle Because of inherent problems associated with general anesthesia in cattle, as well as economics, regional nerve blocks are common in this species. In fact, most orbital, eyelid, conjunctival, and corneal surgery is performed with regional injectable anesthesia. Of the three different routes for orbital injections of regional anesthesia in the cow, i.e., Peterson’s, Schreiber’s, and Hare’s, Peterson’s is the most common in America, but somewhat more difficult. A relatively simple method in cattle, the four-point block, uses more local anesthetic than the Peterson method, and delivers retrobulbar anesthetic through the dorsal, medial, lateral, and ventral conjunctival fornices directly into the retrobulbar space (see Chapter 3). In Peterson’s regional nerve block, an 8–10 cm, 18–20 g needle is inserted at the posterior angle of the zygomatic arch and lateral orbital rim, and directed anterior of the coronoid process of the mandible and inferomedially to the pterygopalatine fossa near the foramen orbitorotundum. After aspiration (avoiding the internal maxillary artery), 15–20 mL of local anesthetic is injected. Successful retrobulbar nerve block is shown as mydriasis, lack of globe mobility, and loss of corneal sensation. The palpebral nerve is blocked by placing 5–10 mL of local anesthetic subcutaneously along the dorsal zygomatic arch.

Complications of retrobulbar injections Retrobulbar injections require care, and can induce retrobulbar hemorrhage. The animal orbit contains large veins and venous plexuses, and hemorrhage sufficient to produce additional pressure of the globe, and even enter the subconjunctival spaces, fortunately occurs infrequently. Aspiration immediately prior to the injection of local anesthetic minimizes this complication. If this occurs, surgery should be delayed until the hemorrhage has reabsorbed.

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The operating room

Inadvertent puncture of the globe with the needle is rare, but a serious complication. The retrobulbar saline is usually reabsorbed within 30–60 min. With the use of intravenous neuromuscular blocking drugs, use of retrobulbar injections to manipulate the globe is less common and may be redundant. A few cases of cattle have been reported to suffer respiratory collapse and sudden death after the Peterson retrobulbar block, presumably from accidental anesthetic injection within the optic nerve meninges or the cerebrospinal space.

Stay sutures Silk stay sutures (usually 4-0), placed in the limbus, deep subconjunctival tissues, and dorsal rectus muscle insertion, may be used to turn and/or pull the globe forward prior to corneal and intraocular surgeries. After placement of the sutures in the ocular tissues, the opposite end of the stay suture is attached to the eyelid speculum, surgical drape or towel clamp, or to a hemostat clamped to the surgical drape. Two stay sutures may be superior to a single suture. Dependent on the site of the stay suture, the globe may be rotated to the desired position. As with retrobulbar injections, traction by these stay sutures on the anterior segment may distort the globe because of the lower ocular rigidity in the dog and cat. Possible complications of this method include tearing of the tissues by the stay suture, usually associated with excessive traction, and rarely penetration of a thin sclera. Stay sutures can also be used to retract the nictitating membrane from the surgical field. The suture is placed fullthickness around the nictitans cartilage, just beneath its leading margin, and extended to and secured to a towel clamp or hemostat anchored in the adjacent drape. The tension on the stay suture is adjusted to position the nictitans away from the surgical site but with no distortion of the globe.

Flieringa or Flieringa–LeGrand fixation rings The Flieringa rings consist of a single ring or two different sizes of stainless steel wire rings that are attached to each other (Fig. 2.9). Single ring sizes range from 12 mm to 22 mm in 1 mm increments. The double Flieringa ring is available in two sizes: 1) small (pediatric): 14 mm inner ring and 23 mm outer ring; and 2) large (adult): 17 mm inner ring and 24 mm outer ring. Wire rings in excess of 23 mm diameter are also easy to self-construct.

These wire rings are attached to the limbus or 1–4 mm posterior to the limbus with four or more simple interrupted 4-0 silk sutures to maintain the corneal wound during surgery and apposition, as well as to prevent collapse of the anterior chamber and globe. As the canine and feline corneas measure 16  15 mm and 17  16 mm, respectively, a selection of the larger ring sizes is recommended. These rings are used to maintain the shape and relative size of the anterior portion of the globe. Although these rings can adequately stabilize the anterior globe of the dog and cat, their use has not been common because of the time necessary to position the ring. The large Flieringa rings (12–24 mm) are recommended when full-thickness keratoplasty is performed in small animals to maintain the corneal curvature and the anterior chamber depth.

General anesthesia/neuromuscular blocking agents Most general inhalational anesthetics cause the globe to rotate down and inward, and decrease exposure to the eye. As a result, stay sutures are frequently used to stabilize and rotate the globe outward to improve surgical exposure. However, there are limits to the traction created by these sutures, and sometimes the surgical exposure is less than satisfactory. The administration of neuromuscular blocking agents, once general anesthesia has been stabilized, provides the optimal exposure of the dog’s globe, and has become the standard for most dog and equine corneal and intraocular surgeries. With paralysis and loss of all extraocular muscle tone caused by these drugs, the entire cornea is accessible. The globe also becomes somewhat hypotonic, usually negating the administration of intravenous osmotic agents to lower intraocular pressure. In fact, parenteral osmotics are not recommended when neuromuscular blocking agents are used for cataract surgery in dogs, because the eye may become too soft. The drug-induced paralysis may also reduce the impact or weight of the retrobulbar tissues on the posterior segment, and decrease the tendency for forward vitreous displacement during cataract surgeries in both dogs and horses. Neuromuscular blocking agents cause paralysis, but are not anesthetics. It is imperative that the level of general anesthesia be sufficient and closely monitored during use of these neuromuscular blocking agents. The section on these agents in Chapter 3 provides additional information and dosage.

Lateral canthotomy

Fig. 2.9 The Flieringa rings can be attached by eight silk sutures to the limbus in small animals to stabilize the anterior segment of the globe and prevent collapse of the anterior chamber.

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The lateral canthotomy procedure is probably the most frequently performed ophthalmic surgery in animals and is often used prior to corneal and intraocular surgeries. Incision of the lateral canthotomy temporarily increases the size of the palpebral fissure and facilitates surgical exposure of the globe. In many breeds of dogs with prominent eyes and for most cats, a lateral canthotomy for most ophthalmic surgical procedures is not necessary. However, in many mesocephalic and nearly all dolichocephalic breeds of dogs, the lateral canthotomy is indicated. Lateral canthotomies can cause postoperative swelling of the lateral canthus and limited discomfort. With the recent use of

Hemostasis

A

B

Fig. 2.10 Lateral canthotomy increases exposure of the cornea and globe. (a) After placement of the eyelid speculum to ascertain exposure, the lateral canthus is incised by curved Mayo or Metzenbaum scissors for 5–15 mm. The length depends on the breed and the required amount of exposure. (b) Two-layer closure includes: tarsoconjunctiva with 4-0 to 6-0 simple continuous absorbable sutures and the orbicularis oculi–skin layer with 4-0 to 6-0 simple interrupted non-absorbable sutures. The first suture (simple interrupted; simple mattress) is carefully placed near the eyelid margin.

neuromuscular blocking agents during ophthalmic surgery in small animals and the horse, the indications and need for lateral canthotomy are more limited. After insertion of an eyelid speculum, the palpebral fissure is maximized and the surgical exposure ascertained. If additional exposure is necessary, a lateral canthotomy is performed with curved Mayo or Metzenbaum scissors (Fig. 2.10a). The lateral canthal eyelid is incised for 5–15 mm, but the incision should not extend beyond the lateral orbital ligament. Hemorrhage is usually negligible. Point electrocautery can control any minor bleeding. A straight mosquito forceps may be used to slightly crush the tissues prior to the incision to control hemorrhage but is not usually necessary. At the conclusion of surgery, the lateral canthotomy is apposed by two layers of sutures in most breeds of dogs; in toy breeds, however, a single layer of sutures will suffice. The palpebral conjunctiva, submucosal fascia, and tarsus are apposed with 4-0 to 6-0 simple interrupted absorbable sutures (Fig. 2.10b). The external layer of closure, consisting of the orbicularis oculi muscle and lid skin, is apposed with 4-0 simple interrupted non-absorbable sutures. The first suture is carefully placed at the eyelid margin and has the greatest tension on it. Occasionally this suture is a modified interrupted mattress pattern. The skin sutures are removed at 7–10 days postoperatively. The most frequent postoperative complications after lateral canthotomy include dehiscence of the first one or two sutures, usually within the first week, and malalignment of the area. In eyes with lateral canthotomies, postoperative medications and ophthalmic examinations should be performed with care to prevent undue tension on the healing lateral canthus and sutures. Routine use of the E-collar in small animals also helps in the maintenance of the lateral canthotomy. Animals can quickly traumatize this area and tear the sutures from the lateral canthus. In the event of local dehiscence, the wound edges are refreshened and apposed by additional sutures.

Problems with enophthalmia Intraocular surgeries in large and giant breeds of dogs may be more difficult because of enophthalmia and limited exposure of the globe. As a result, surgery must be performed with the globe recessed in the orbit and certain

manipulations may be limited. With time and exposure, the bulbar and palpebral conjunctiva can become edematous and swollen, limiting further the surgical exposure. Attempts to improve access to the globe with lateral canthotomy, retrobulbar injections, and stay sutures are usually less than satisfactory. Excessive pressure on the globe, associated with suture or instrument traction on the anterior globe, or injections of solutions behind the posterior globe, may collapse and distort the globe, increasing the difficulty and duration of the intraocular surgery.

Hemostasis Maintenance of adequate hemostasis is essential for all ophthalmic surgical procedures. Uncontrolled intraoperative bleeding will diminish the visualization of critical ophthalmic structures. Any volume of blood retained within the surgical wound may retard wound healing, increase scarring, and cause immediate distortion of the postoperative wound. Intraocular hemorrhage is also unacceptable, and may promote the formation of synechiae and pupillary and preiridal inflammatory membranes. Hemostasis for most corneal and intraocular surgical procedures relies on direct pressure on the small bleeders, point electrocautery, and intraocular adrenaline (epinephrine). Temporary clamping of the larger conjunctival or subconjunctival blood vessels with a small hemostat is rarely necessary.

Electrocautery Electrocautery units are employed primarily to coagulate blood vessels for hemostasis in ophthalmic surgery in small animals, but are not used for the cutting of ocular tissues, except occasionally the bleeding iris. Unfortunately, cutting by electrocautery units may penetrate deeper than expected, and therefore constitutes a critical limitation for ophthalmic surgery. Generally, the small electrocautery units are most adequate and safest for ophthalmic surgery. Several battery-powered portable cautery units are available (Fig. 2.11a,b) as well as AC units (Fig. 2.11c) that provide wet-field cautery. The hand-held units are inexpensive, battery powered, and possess small microtips. The batteries are long-lasting, but must be removed during sterilization and replaced immediately before surgery. Wet-field cautery units are effective in the presence of blood, have limited systemic effects, and do not require patient grounding.

Local adrenaline (epinephrine) The addition of 1:100 000 adrenaline (epinephrine) to moistened cotton swabs can be used for hemostasis associated with small bleeders during conjunctival and corneal surgery; however, the concurrent use of halothane as an inhalational anesthetic may preclude its use. If adrenaline (epinephrine) is used for hemostasis in ophthalmic surgery, it is generally reserved for intraocular surgery where other modalities cannot be used, and is used at higher concentrations (1:1000). If adrenaline (epinephrine) is expected to be used for hemostasis, as during the repair of a full-thickness corneal laceration with iris prolapse, isoflurane should be the inhalational anesthetic.

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A

B

C

Fig. 2.11 Examples of portable and battery-powered hand-held ophthalmic cautery units. (a) Hand-held battery-power cautery unit. Unit can be steam sterilized and the batteries placed in the unit just before surgery. (b) Disposable battery-powered cautery. (c) Wet-field coagulator. Unit may be AC or batterypowered.

Electroepilation Electroepilation or electrolysis is used to treat canine distichiasis, trichiatic lashes, and ectopic cilia. The objective is to provide low levels of direct current to the hair follicle and destroy the germinal hair cells. For the most effective electrolysis, accurate placement of the electrolysis needle is paramount. Electrolysis is primarily employed when only a few distichia require treatment. Good magnification, illumination, and stabilization of the eyelid margin are important considerations. All electrolysis units have a very fine needle that can be inserted directly into the hair follicle. After 15–30 s of low milliamperage (2–4 mA) small bubbles will appear at the hair follicle opening. These bubbles are formed by hydrogen released by the electrolysis of the basal hair cells. With removal of the electrolysis needle, the offending distichia will usually be withdrawn. Occasionally small cilia forceps are necessary to epilate the distichia after electrolysis. Inadequate electrolysis can result in recurrence of the distichia. Excessive electrolysis can result in inflammation and fibrosis of the eyelid margin. Electrolysis is also less successful when multiple distichiae emerge from a single orifice, which unfortunately is quite frequent. The insertion of the electrolysis needle into each hair follicle is not usually possible and regrowth is common. Additional information on electroepilation can be found in Chapter 5. Several portable electroepilation units are available, and because of the low levels of current necessary they are usually battery powered. Units that provide 2 or 4 mA are safe and the least likely to produce excessive electrolysis (Fig. 2.12). Larger units that consist of the base and battery, manually controlled rheostat, milliamperage gauge, and the hand-held microstylet provide the most consistent results.

of mainly collagen fibers, are relatively unaffected by cryotherapy. The cryoadhesion developed between a cryoprobe and lens necessitates only direct contact, and with the more powerful units can occur even in the presence of aqueous humor and vitreous. Although cryotherapy has been evaluated for many corneal and intraocular surgical procedures in small animals, the primary indications include the treatment of distichiasis and small eyelid tumors, cryoextraction of subluxated, anteriorly and posteriorly luxated lenses, transscleral cyclocryotherapy for the partial destruction of the ciliary body for treatment of glaucoma, and chorioretinal cryotherapy for treatment of localized retinal tears and detachments. There are several different types of cryo-instruments. Those units that use CO2 (–78 C), nitrous oxide (–89 C), and liquid nitrogen (–195 C) are the most versatile. Some cryounits consist of a gas tank and hose, a base unit (often with tank pressure and probe temperature dials), and a hand-held probe (Fig. 2.13). The Frigitronics and Cabot Medical cryo-instruments, as well as the Brymill portable units (Fig. 2.14), are the more frequently used units in veterinary ophthalmology. For accurate cryotherapy, monitoring of the tissue temperature around the cryoprobe is useful for eyelid procedures.

Cryotherapy Cryotherapy in veterinary ophthalmology offers another therapeutic modality for certain ophthalmic disorders. Cryotherapy offers two unique characteristics: 1) selective destruction of normal and neoplastic tissues; and 2) increased adhesion that develops between the cryoprobe and ocular tissues. Ocular tissues sensitive to cryodestruction include the corneal epithelium and endothelium, all intraocular blood vessels, ciliary body epithelium, uveal pigment cells, and the retina. The corneal stroma and sclera, consisting

26

Fig. 2.12 Small battery-powered epilation unit.

Laser therapy

Fig. 2.13 Liquid nitrogen unit for ophthalmic use. (a) Base unit for the cryotherapy. (b) Cryoprobes. Top: cataract, straight; bottom: glaucoma, curved.

B

A

The tip of the small probe is usually covered with a thermal shield to prevent damage or adhesion to adjacent tissues during the cryotherapy. There are usually several different selections of probes for veterinary ophthalmology: the straight cataract (tip diameter 1–2 mm) and slightly curved glaucoma

probes (tip diameter 3–5 mm) are the most useful. Probe tip temperature during cryotherapy should rapidly achieve and maintain temperatures ranging from 30 C for cryoadhesion to 80 C to 90 C for cryodestruction. For cyclocryotherapy, liquid nitrogen is recommended as the coolant. To achieve epithelial destruction of the ciliary body at 20 C to 30 C, the probe tip temperature must be at least 70 C to 90 C. For treatment of distichiasis and eyelid neoplasms, and cyclocryotherapy for end-stage glaucoma, lower cost handheld portable liquid nitrogen units are useful. These units have a generous assortment of open (spray) and closed cryoprobes for ophthalmic use.

Laser therapy Laser therapy was first introduced in human ophthalmology in the 1960s, and quickly these ophthalmologists recognized the benefits of the laser. The eye is an ideal organ for laser therapy with its tissues and media usually clear, and the target tissues usually heavily pigmented. Laser use was first reported in veterinary ophthalmology in the 1980s, once the laser units became considerably smaller, portable, and less expensive.

Laser basics

Fig. 2.14 A less expensive hand-held portable cryounit with variable open (spray) and closed probes can be used for extraocular use and transscleral cyclocryothermy.

Lasers emit light energy; this energy is transmitted to the target tissues, and absorbed selectively by pigmented tissues. There are several types of commercial laser, and each emits energy of specific wavelengths. Each ocular tissue absorbs a particular range of wavelength. The cornea absorbs short

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ultraviolet wavelengths (200–313 nm) and greater than the longer infrared wavelengths (1400–10 000 nm). The lens absorbs ultraviolet wavelengths (315–400 nm), thus protecting the retina from harmful ultraviolet rays from the sun. The blue, blue–green, yellow, red, and near-infrared spectrum of wavelengths (400–1400 nm) pass through the sclera and clear cornea, aqueous humor, lens, and vitreous to be absorbed by the fundic tissues (melanin and hemoglobin). Three ocular pigments absorb the majority of laser energy delivered to the eye; they include melanin, hemoglobin, and xanthophyll (in the human macula). Melanin within the uveal tract and retinal pigment epithelia absorbs the visible and infrared wavelengths (400–1400 nm), and absorption increases as the laser wavelength decreases. Within the retina there may be different absorptions by the individual retinal tissues: 1) short or blue wavelengths are absorbed better by the inner retinal layers; 2) yellow wavelengths are absorbed better by red subretinal neovascular membranes; 3) longer wavelengths in the infrared red range penetrate the sclera better; and lastly, 4) the longer the wavelength, the greater the tissue transmission.

Laser delivery From the laser source, the energy is delivered to the ocular tissues by different avenues. Laser energy may be delivered using a number of transscleral probes in the contact or non-contact mode, as with the neodymium:yttrium aluminum garnet (Nd:YAG) laser. It may also be delivered by endoprobes within the eye, the indirect ophthalmoscope with laser attachment for transcorneal and transpupillary transmission, the slit-lamp biomicroscope, and as an adapter to the operating microscope.

Laser choice Choice of laser by the veterinary ophthalmologist is dependent on its range of clinical use (target ocular tissues and their wavelength absorption ranges), type of intended tissue damage (thermal photocoagulation, photodisruption, photoablation, and/or photochemical), portability, and cost. Lasers can also be used in the continuous wave

mode or in the pulsed mode, which can change the tissue damage they cause. Using the Nd:YAG laser in the continuous mode causes thermal photocoagulation; the same laser in the pulsed mode (either Q-switching with nanosecond pulses or mode-locking with picosecond pulses) produces a photodisruptive effect.

Current ophthalmic lasers Ophthalmic lasers currently commercially available include the CO2, excimer, argon, tunable dye, Nd:YAG, and diode. Their characteristics and veterinary ophthalmic use are summarized in Table 2.1. Of these instruments, the diode laser is the laser most frequently used by the veterinary ophthalmologist; its tissue damage is caused by photocoagulation (Fig. 2.15). The second most frequently used laser is the Nd:YAG laser used in both the contact and non-contact mode; this unit is also shared with veterinary surgeons (Fig. 2.16). The diode laser has a shorter wavelength (810 nm) than the Nd:YAG laser (1064 nm) which allows improved melanin absorption, but less transscleral transmission than the Nd:YAG laser. Diode transscleral transmission can be increased by use in the contact mode. The diode laser also permits transcorneal, transpupillary, and intravitreal (endoscopic laser) energy delivery.

Laser applications In the specialty practices of veterinary ophthalmology world-wide, the diode laser is the most frequently used instrument. Its advantages include high absorption of its energy by melanin, portability (small and lightweight), and low cost. Less frequently used lasers include the Nd: YAG (delivered by contact probe or by slit-lamp biomicroscope) and CO2; the latter is used for the treatment of adnexal, conjunctival, and episcleral lesions in small animals and the horse. Experimental laser refractive surgery or keratomileusis has been performed in the dog, but it is doubtful that it will become useful clinically. The diode, Nd:YAG, and CO2 lasers have been used to treat limbal or epibulbar melanomas in dogs and cats with high success. These lasers are less invasive, faster, excellent for hemostasis, and less technically difficult. The result is charring and

Table 2.1 Lasers used in veterinary ophthalmology

Laser type

Wavelength (nm)

Tissue damage

Clinical use

Excimer

193

Photoablation

Epithelial and anterior stroma keratopathies, LASIK

Argon

488–514

Photocoagulation

Retinal photocoagulation, iridotomy, iridoplasty, sclerostomy

Diode

810

Photocoagulation

Cyclophotocoagulation, retinal photocoagulation, iridotomy, sclerostomy

Nd:YAG (continuous mode)

1064

Photocoagulation

Cyclophotocoagulation, capsulotomy, cataract surgery

Nd:YAG (Q-switched or mode locked)

1084

Photodisruption

Retinal photocoagulation, iridotomy, sclerostomy, hyaloidotomy

CO2

10 600

Photoablation

Blepharoplasty, conjunctival carcinoma, punctoplasty

Modified from Gilmour MA 2002 Lasers in ophthalmology. In: Bartels KE (ed.) Lasers in Medicine and Surgery. WB Saunders, Veterinary Clinics of North America: Small Animal Practice 32:649–672.

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Laser therapy

A

B

Fig. 2.15 The diode laser system is the most popular system in veterinary ophthalmology. (a) The base unit is small and portable. (b) The diopexy hand probe for retinopexy (left); a separate hand probe is necessary for transscleral cyclophotocoagulation (right). (c) The unit can also be mounted on an indirect ophthalmoscope for transpupillary retinopexy. (Photographs courtesy of Iridex Corporation, Mountain View, CA USA)

C

Fig. 2.16 The Nd:YAG laser is available mounted as part of the slit-lamp biomicroscope as in this illustration or as a base unit with hand probes. The former is used for transpupillary iridotomy, hyaloidotomy, and synechiotomy; the latter is used for transscleral cyclophotocoagulation.

contraction of the pigmented mass, and low levels of recurrence. The diode laser delivery systems include indirect ophthalmoscope with a 20 D lens, operating microscope adapter, and either the glaucoma or transscleral non-contact probe. Laser cyclophotocoagulation is commonly used by veterinary ophthalmologists for treatment of canine, feline, and equine glaucomas. The transscleral and recent endoscopic laser photocoagulation methods attempt to partially destroy the ciliary body processes and reduce aqueous humor formation rates. Exact placement of the laser probe during the transscleral methods is essential for ciliary body ablation, and is addressed in the endoscopic method by directly observing the ciliary processes during lasering. Results of laser therapy for the different glaucomas and species are available in Chapter 10.

Both diode and Nd:YAG lasers have been used for synechiotomy, capsulotomy, iridotomy for pupillary block glaucoma, and hyaloidotomy for malignant glaucoma with variable success. Experimentally, the diode laser delivered by the direct ophthalmoscope system in the normal dog failed to produce patent iridotomies either grossly or microscopically. Laser therapy of canine opacified posterior capsule has been attempted with both diode and Nd:YAG lasers. For additional information, see Chapter 10. Both diode and Nd:YAG lasers have been used to treat large uveal cysts (dogs and horses) and cystic corpora nigra (horses) which have the potential to interfere with vision. These cysts deflate during lasering, and may detach and fall into the ventral anterior chamber. Variable fibrin and slight hemorrhage are possible minor complications. Both diode and Nd:YAG lasers have been used in dogs and a few horses to treat primary intraocular neoplasia. Laser energy can be delivered transsclerally, transcorneally or by a sterile fiber inserted through the opposite pars plana into ciliary body tumors. Use of laser therapy for canine intraocular tumors is influenced directly by the following facts: 1) most canine intraocular tumors involve the anterior uvea; and 2) the metastatic rates for these tumors are very low (perhaps 5%). One study in dogs using the Nd:YAG laser to treat both ciliary body and iridal tumors suggested that success was influenced mainly by the extent or size of the tumor and less by tumor pigmentation. Melanomas in the retriever breeds primary involve the anterior iris surface, and are quite successfully treated by either the Nd:YAG or diode laser. Additional information is available in Chapter 9. Laser therapy is a mainstay for the treatment of vitreoretinal diseases, for which the preferred laser is the diode, with its energy delivery transsclerally, transpupillary, and by endophotocoagulation during pars plana retinal detachment surgery. Diode laser or cryotherapy is used to perform retinopexy, either prophylactically or for the treatment of rhegmatogenous retinal detachment surgery. For additional information, see Chapter 12.

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Laser safety As laser energy is potentially hazardous to veterinary ophthalmologists and their staff, several safety precautions are essential. As each laser emits its own range of wavelength energy, all precautions must be based on the selected laser. Laser safety eyewear must be worn whenever laser use occurs. When lasering an eyelid lesion, the patient’s eye must be protected with a non-reflective stainless steel or lead eye shield. Any window within the laser room should be shuttered and doors locked with dead-bolts when the laser is in use.

Table 2.2 Drugs to support corneal and intraocular surgical procedures*

Agent

Purpose

Antifibrin agents

Heparin (1–2 IU/mL) mixed in all topical and intraocular irrigating solutions (usually lactated Ringer’s). To prevent fibrin formation during surgery Tissue plasminogen activator (intracameral): 25 mg to treat fibrin and blood clots (up to 10– 14 days old)

Perioperative drugs Several drugs should be available in the ophthalmic operating room for corneal and intraocular surgical procedures in animals (Table 2.2). These drugs may be administered topically before and after surgery, and injected in the anterior chamber during surgery. All drugs used intraocularly must be sterile and without preservatives. Drugs delivered topically may be placed on the cornea by an operating technician. Drugs injected into the anterior chamber or elsewhere should be administered by the surgeon. The general classes of drugs that should be immediately available to the veterinary ophthalmic surgeon include antifibrin drugs, antibiotics, anti-inflammatory agents, miotics and mydriatics, irrigating solutions, and viscoelastic substances. These drugs may be administered topically, intracamerally (injected directly into the anterior chamber), or injected subconjunctivally beneath the bulbar conjunctiva. Fibrin is an undesirable sequela of anterior uveitis in small animals, and often occurs after the anterior chamber has been entered. The two most useful antifibrin drugs are heparin and tissue plasminogen activator. Heparin (1–2 IU/mL) may be added to all topical and intracameral irrigating solutions, thus impairing fibrin formation as the surgical procedure is performed. If intraocular hemorrhage occurs, the administration of irrigating solutions with heparin is temporarily stopped to permit clotting. Heparin irrigating solutions can often be resumed later in the surgical procedure. Later the blood clot may be irrigated or gently removed by forceps. In the event that excessive fibrin or clot formation occurs postoperatively, tissue plasminogen activator (tPA) may be injected. tPA is a clot-specific fibrinolytic agent developed by gene cloning; it forms a complex with fibrin, activating plasminogen into plasmin that lyses fibrin, fibrinogen, and other procoagulant proteins into soluble by-products. As a result, the fibrin clot breaks down and is reabsorbed. tPA is maintained frozen in 25 mg doses in individual 1 mL syringes ready for injection into the anterior chamber, usually several days after corneal and intraocular surgeries when excessive fibrin has formed. tPA injections appear effective in dissolving most fibrin clots in the anterior chamber that are less than 7–14 days’ duration and in all species. Antibiotics may be administered perioperatively by the topical route as well as by intracameral injection. Topical antibiotics are the standard ophthalmic solutions and ointments, and are usually instilled on the cornea at the conclusion of corneal and intraocular surgeries. Intracameral antibiotics may be injected into the anterior chamber when

30

Antibiotics (add to the irrigating solution for topical and intracameral use)

Penicillin G (1000–4000 IU/mL) Chloramphenicol (1–2 mg)

Anti-inflammatory agents Corticosteroids:

1.0% prednisolone for topical use Methylprednisolone and/or triamcinolone for subconjunctival injections

Non-steroidal anti-inflammatory agents for topical use: Flurbiprofen and suprofen Control of pupil Miotics:

Topical 1% to 2% pilocarpine Intracameral 1:100 acetylcholine chloride

Mydriatics: Topical 1% tropicamide and 1% atropine Subconjunctival atropine Intracameral 1:1000 adrenaline (epinephrine) Topical and intracameral sterile irrigating solutions

Saline, balanced salt solution, and lactated Ringer’s solution

Intraocular hemostasis

Intracameral 1:1000 adrenaline (epinephrine)

Viscoelastic compounds

1% sodium hyaluronate 2% hydroxypropyl methylcellulose 4% sodium chondroitin sulfate plus 3% sodium hyaluronate

*All intracameral drugs should be sterile, without preservatives, and for single use for injection into the anterior chamber.

infection may be present (with full-thickness corneal lacerations or corneal ulcerations), or added to the irrigating solutions used throughout the entire surgical procedure. The concentrations of intracameral antibiotics must be very low to avoid direct damage to the corneal endothelium, and broad spectrum to provide maximum effectiveness.

Patient recovery/restraint

Preoperative treatment with topical and systemic antibiotics to temporarily sterilize the conjunctival and corneal surfaces is not usually successful. In one study, bacterial contamination of the anterior chamber of the dog during cataract surgery occurred in about 30% of the treated eyes. These bacteria, usually staphylococcal species, undoubtedly contribute to the intensity of postoperative anterior uveitis in small animals after intraocular surgeries. As a result, topical and systemic antibiotics are usually administered for a few days preoperatively and for 5–7 days postoperatively. Additional antibiotics may be used intracamerally and the reader should consult ophthalmic pharmacology texts for recommended doses. Anti-inflammatory drugs are essential to control the postoperative inflammations that occur after the dog or cat anterior chamber has been opened. Topical and systemic corticosteroids are usually administered to treat anterior uveitis that can occur after corneal and intraocular surgeries. Corticosteroids may be injected subconjunctivally to provide an additional route to treat the severe forms of anterior uveitis. Topical and systemic non-steroidal antiinflammatory agents are also administered pre- and perioperatively in small animals for concurrent anterior uveitis. During anterior uveitis and upon surgical entry into the anterior chamber, prostaglandins released from the uveal tissues stimulate a rapid miosis, breakdown of the blood– aqueous barrier, and the formation of fibrin in the aqueous humor. These non-steroidal anti-inflammatory agents in the dog appear very useful in the maintenance of a widely dilated pupil during and after lens removal. In intraocular surgery, control of the pupil may be critical during the surgical procedure and in the postoperative period. Miotics to constrict the pupil may be administered topically (usually 1–2% pilocarpine) or injected intracamerally with 1:100 acetylcholine chloride when an immediate miosis is necessary. Intracameral miotics should be sterile, single use, and free of preservatives. Constriction of the pupil may be an immediate complication during surgical entry of the anterior chamber. Pre- and perioperative topical mydriatics and non-steroidal antiinflammatory agents assist in the maintenance of a widely dilated pupil during surgery. Intracameral adrenaline (epinephrine) (1:1000) may also be injected to induce an immediate mydriasis when the anterior chamber has been opened. As some adrenaline (epinephrine) is absorbed systemically in patients in which pupil control may be difficult, isoflurane is the recommended general anesthetic. Atropine sulfate may also be injected subconjunctivally at the conclusion of intraocular surgery to help achieve mydriasis during the immediate postoperative period when pupil movement is still possible. Sterile isotonic solutions are maintained in the ophthalmic operating room to irrigate corneoconjunctival surfaces, and lavage the anterior chamber during intraocular surgeries. The most frequently used solutions are sterile 0.9% saline for topical use and lactated Ringer’s solution for intracameral use. Sometimes other drugs, such as heparin and antibiotics, are added to these solutions during corneal and intraocular surgeries. Two additional groups of drugs are used commonly in small animal and equine ophthalmic surgery. Viscoelastic agents are very viscid solutions used to maintain the anterior

chamber during corneal and intraocular surgeries. They are available, ready for use during surgery, in 1 mL and 2 mL sterile syringes. These agents are designed to coat and protect the corneal endothelium during phacoemulsification and the insertion of an IOL, fill and maintain the anterior chamber, expand the capsular bag for IOL implantation, and temporarily increase intraocular pressure. They are also useful to maintain the anterior chamber during the repair of full-thickness corneal lacerations. These agents can also be used to manage miosis, intraocular hemorrhage, posterior capsular tears, and vitreous presentation. Viscoelastic agents are divided, based on their physical properties, into: 1) cohesive (high viscosity/molecular weight); and 2) dispersive (low viscosity/molecular weight). Cohesive agents tend to aggregate and remain together. Dispersive agents tend to occupy the available space and spread apart. Cohesive agents are better to create space, expand the capsular bag, dilate pupils, and move tissues. In contrast, the dispersive viscoelastics are better to coat surgical instruments, and corneal endothelium and epithelium, partition trouble areas, and tamponade posterior capsular tears. The supercohesive viscoleastics may contribute more to postoperative ocular hypertension. The dispersive viscoelastics remain longer in the anterior chamber after injection, and offer better protection of the corneal endothelium during phacoemulsification. Selected viscoelastics include: HealonW (Pharmacia–Upjohn), a cohesive viscoelastic; ViscoatW (Alcon Laboratories), a dispersive viscoelastic; Healon GVW (Pharmacia–Upjohn), a supercohesive viscoelastic; and DuoViscW (Alcon Laboratories), a combined cohesive and dispersive viscoelastic. Although not listed in Table 2.2, a new group of drugs has recently been added for use in the ophthalmic operating room. Antifibrotic agents are now being used intraoperatively and postoperatively for the different antiglaucoma filtering and anterior chamber shunt surgeries. Excessive fibrous capsule formation often surrounds and eventually impairs the egress of aqueous humor through these surgical fistulae. Freshly mixed mitomycin C has been used in dogs intraoperatively during different glaucoma surgical procedures to prolong their function. Additional details on mitomycin C can be found in Chapter 11.

Patient recovery/restraint Several methods have been developed by veterinarians to restrain animals in order to prevent self-trauma. The technique most useful after most types of small animal ophthalmic surgery is the application of an Elizabethan collar (Fig. 2.17). These collars effectively prevent the animal from touching the eyelids, adjacent orbital areas, and the eye with either front or back paws, as well as from rubbing the operative site on the floor or other objects. The Elizabethan collar is available commercially manufactured from plastic, nylon or cardboard materials, or can be self-constructed from cardboard, X-ray film, or from plastic buckets or waste baskets. Stronger materials, such as plastic collars, buckets, and waste baskets, are recommended for dogs over 20 kg; cardboard or X-ray film collars may be used for smaller dogs and cats. For a self-constructed Elizabethan collar, the collar diameter is approximately 4–8 cm beyond the patient’s

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In horses, eyelid, conjunctival, and corneal sutures can also cause postoperative discomfort. Unprotected, the horse can rub the surgical wound sufficient to cause wound dehiscence and marked swelling, loss of hair and open skin wounds. There are several methods to prevent or minimize this self-induced trauma; they include a neck cradle, cross-tying the horse, and preferably a face mask with hard eye cups to protect either the right or left, or both eyes. As moisture can collect under these masks, frequent cleaning and drying the area can markedly prolong their use.

Subpalpebral medication systems Fig. 2.17 A self-constructed or commercially available Elizabethan collar is an effective deterrent against self-mutilation after ophthalmic surgery. The collar should extend 4–8 cm beyond the animal’s nose and utilized until the eyelid/lateral canthotomy sutures have been removed.

nose. The collar is secured to the neck with gauze bandage tied loosely. Excellent alternatives are plastic buckets or waste baskets. A circle is cut from the bottom of the container sufficient to slide over the head and fit loosely about the neck. A leather or gauze bandage collar is threaded through four or more holes punched in the base of the container to secure the device to the animal’s neck. The Elizabethan collar, commercial or self-constructed, should fit tight enough to prevent its dislodgement, but loose enough to prevent any breathing and eating problems. Other restraint methods include hobbles for the front paws, and/or covering the front paws with bandages or socks. Small animals can still rub the postoperative eye with these devices. Short-term postoperative sedation and tranquilization may also be used to calm a dog or cat, but their use is usually restricted to only a few days.

A

Subpalpebral medication systems were developed for small animals and horses nearly 40 years ago, and have been employed routinely in horses. These systems consist of tubing with or without a footplate that is placed in the animal’s dorsal, dorsolateral or ventral conjunctival fornix (Fig. 2.18), and continued through the eyelid to terminate on the animal’s forehead or upper neck. The subpalpebral system permits medication with solutions of the small animal’s eye while covered with a complete temporary tarsorrhaphy. This system also provides for a reliable system to deliver medications to the horse eye which is painful and difficult to treat as frequently as necessary. The system can be self-constructed from silicone or polyethylene tubing with footplates (Fig. 2.19), and is available commercially (often referred to as one-hole systems). Simple silicone tubing may also be used and placed into the conjunctival fornix through two holes in the upper eyelid. A third system uses an indwelling catheter in the horse’s nasolacrimal duct via the false nostril. As topical medications may persist in the horse’s nasolacrimal duct, this route may be associated with greater systemic absorption of topical ophthalmic drugs, especially atropine.

B

Fig. 2.18 Placement of a subpalpebral system in the standing horse. (a) The supraorbital nerve block is performed (inject 3–5 mL of local anesthetic into the subcutaneous tissues above the supraorbital foramen) to provide local anesthesia and akinesia of the central upper eyelid. The cornea is anesthetized with a few drops of topical anesthetic. Alternate sites include the lateral canthus and central ventral conjunctival fornix. (b) A 12–14 g hypodermic needle is inserted beneath the central upper lid and into the dorsal conjunctival fornix to exit the entire eyelid.

32

Subpalpebral medication systems

C

C

Fig. 2.18, cont’d (c) The subpalpebral tubing is carefully threaded into and through the needle, leaving the footplate within the upper fornix. (d) The subpalpebral tubing is attached to the patient’s skin with either sutures or hospital tape, and usually terminates in the neck region (where the medications can be injected). As the footplate can migrate towards the limbus from the intermittent eyelid movements, its position within the fornix is checked daily. This scheme allows convenient and reliable delivery of medications to horses at any daily frequency.

Fig. 2.19 Footplate of a polyethylene subpalpebral system placed in the dorsolateral conjunctival fornix in a dog. With the footplate within the conjunctival fornix, direct contact and damage to the cornea is avoided. As contractions by the orbicularis oculi will gradually force the footplate toward the cornea, daily inspection of the footplate is recommended. The subpalpebral system permits topical medication of an eye in any animal species covered by a complete temporary tarsorrhaphy.

In small animals the system is placed while the animal is still under general anesthesia. In the horse, the standing patient is either sedated or the system placed at the conclusion of surgery. When the subpalpebral system is used in small animals, an Elizabethan collar is also recommended to prevent the animal from dislodging the system. In horses, a soft or hard cup with

a face mask is used to prevent dislodgement and rubbing of the system. The medication solutions are placed in a small syringe and injected in the tubing as frequently as necessary. The administration of topical drugs in horse ensures delivery of the drug(s) to the eye and reduces the possibility of injury to the treatment personnel. The powerful orbicularis oculi muscle can gradually move the subpalpebral footplate toward the limbus and peripheral cornea. If the footplate touches the cornea, ulceration can result. As a preventive measure, daily inspection of the footplate position is recommended. Suture tension above the upper eyelid on the subpalpebral system, as well as a silicone disk glued to the tubing external to the lid surface, are also possible. Placement of the subpalpebral system in the lower conjunctival fornix is another strategy. Because knowledge of drug interactions is unknown, ophthalmic medications are mixed only during injections into the system. Battery-powered and micro-osmotic pumps have been used to deliver medications in very low volumes continuously and need further research. Complications in horses with home-made subpalpebral systems, constructed from polyethylene tubing, depend on the experience of the nursing staff, construction of these systems, and the duration of their use. The commercial systems are constructed of silicone tubing, the silicone footplates are larger and glued to the end of the tubing, and the systems are more flexible and resistant to breakage and leaks. These subpalpebral systems are often used to deliver topical medications to an equine patient’s eye for several weeks. As with any catheter system used for several weeks in horses, local wound care and disinfection of the subpalpebral lid site is recommended. One study involving 150 horses reported the advantages and relative safety of subpalpebral medication systems. The key is close daily inspection of the system footplate, and correction of any positional changes as the powerful orbicularis oculi muscle forces it toward the limbus and cornea. It must remain safely within the conjunctival fornix to prevent any direct corneal contact and damage.

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2

The operating room

In the same study, minor complications (34%) included mild lid swelling, tearing of the system, and loss of the injection cap (end of the tubing where topical medications are injected). All of these complications are manageable and may, in part, be associated with self-induced trauma by the patient. More severe complications (24%) included premature tubing removal, focal infection of the eyelid, loss of the footplate, and corneal ulceration (1 eye in 150 horses). In another study involving 101 horses using home-made silicone systems, the duration of the subpalpebral systems

ranged from 1 to 14 weeks. Complications were noted in only 15 patients and included corneal ulceration (4 horses), lid swelling (5 horses), conjunctival irritation (2 horses), leaking tubing (2 horses), catheter loss (1 horse), and lid abscess (1 horse). None of these complications prevents reimplantation of another subpalpebral system if the eye disease requires extensive topical therapy. Intensive topical therapy without a subpalpebral system for in pain and difficult horses is unreliable at best, dangerous for the nursing staff, and generally not possible long term (several weeks).

Further reading Preoperative preparation and general Boes DA, Lindquist TD, Fritsche TR, Kalina RE: Effects of povidone–iodine chemical preparation and saline irrigation on the perilimbal flora, Ophthalmology 99:1569–1574, 1992. Boothe HW: Antiseptics and disinfectants, Vet Clin North Am: Small Anim Pract 28:233–248, 1998. Fowler JD, Schuh JCL: Preoperative chemical preparation of the eye: a comparison of chlorhexidine diacetate, chlorhexidine gluconate, and povidone–iodine, J Am Anim Hosp Assoc 28:451–457, 1992. Gelatt KN, Gelatt JP: Handbook of Small Animal Ophthalmic Surgery, Extraocular procedures, vol 1, Oxford, 1994, Pergamon, pp 11–21. Gelatt KN, Gelatt JP: Handbook of Small Animal Ophthalmic Surgery, Corneal and intraocular procedures, vol 2, Oxford, 1995, Pergamon, pp 15–30. Roberts S, Severin GA, Lavach JD: Antibacterial activity of dilute povidone–iodine solutions used for ocular surface disinfection in dogs, Am J Vet Res 47:1207–1210, 1986.

Electrosurgery/electroepilation Greene JE: Electrosurgery. In Bojrab MJ, editor: Current Techniques in Small Animal Surgery, ed 3, Philadelphia, 1990, Lea and Febiger, pp 40–41. Halliwell WH: Surgical management of canine distichia, J Am Vet Med Assoc 150:874–879, 1967. Lawson DD: Canine distichiasis, J Small Anim Pract 14:469–478, 1973. Long RD: Treatment of distichiasis by conjunctival resection, J Small Anim Pract 32:146–148, 1991. Stades FC, Gelatt KN: Diseases and surgery of the canine eyelids. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2007, Blackwell, pp 563–617.

Cryotherapy Chambers ED, Slatter DH: Cryotherapy (N2O) of canine distichiasis and trichiasis: an experimental and clinical report, J Small Anim Pract 25:647–659, 1984.

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Magrane WG: Cryosurgical lens extraction: uses and limitations, J Small Anim Pract 9:71–73, 1968. Merideth RE, Gelatt KN: Cryotherapy in veterinary ophthalmology, Vet Clin North Am: Small Anim Pract 10:837–846, 1980. Roberts SM, Severin GA, Lavach JD: Cyclocryotherapy – Part II. Clinical comparison of liquid nitrogen and nitrous oxide cryotherapy on glaucomatous eyes, J Am Anim Hosp Assoc 20:828–833, 1984. West CS, Barrie KP: The use of cryosurgery in a veterinary ophthalmology practice, Semin Vet Med Surg 3:77–82, 1988. Wheeler CA, Severin GA: Cryosurgical epilation for the treatment of distichiasis in the dog and cat, J Am Anim Hosp Assoc 20:877–884, 1984.

Lasers Bacharach J, Lee DA: Iridotomy, trabeculoplasty and trabecular ablation. In Berlin MS, editor: Lasers in Ophthalmology, Ophthalmology Clinics of North America, vol 6, Philadelphia, 1993, WB Saunders, pp 425–436. Bosniak SL, Ginsberg G: Laser eyelid surgery: evaluating the therapeutic options. In Berlin MS, editor: Lasers in Ophthalmology, Ophthalmology Clinics of North America, vol 6, Philadelphia, 1993, WB Saunders, pp 479–490. Brinkman MC, Nasisse MP, Davidson MG, et al: Neodymium:YAG laser treatment of iris bombe´ and pupillary block glaucoma, Progress in Veterinary and Comparative Ophthalmology 2:13–19, 1992. Cook CS: Surgery for glaucoma, Vet Clin North Am: Small Anim Pract 27:1109–1129, 1997. Cook CS, Wilkie DA: Treatment of presumed iris melanoma in dogs by diode laser photocoagulation: 23 cases, Vet Ophthalmol 2:217–225, 1999. English RV, Nasisse MP, Davidson MG: Carbon dioxide laser ablation for treatment of limbal squamous cell carcinomas in horses, J Am Vet Med Assoc 196:439–442, 1990. Fankhauser F, Fankhauser-Kwasniewska S, England C, van der Zypen E: Laser

cyclophotocoagulation in glaucoma therapy. In Berlin MS, editor: Lasers in Ophthalmology, Ophthalmology Clinics of North America, vol 6, Philadelphia, 1993, WB Saunders, pp 449–472. Gilger BC, Davidson MG, Nadelstein B, et al: Neodymium:yttrium aluminum garnet laser treatment of cystic granula iridica in horses: eight cases (1988–1996), J Am Vet Med Assoc 211:341–343, 1997. Gilmour MA: Lasers in ophthalmology. In Bartels KE, editor: Lasers in Medicine and Surgery, Veterinary Clinics of North America: Small Animal Practice, vol 32, Philadelphia, 2002, WB Saunders, pp 649–672. Lin CP: Laser-tissue interactions: basic principles. In Berlin MS, editor: Lasers in Ophthalmology, Ophthalmology Clinics of North America, vol 6, Philadelphia, 1993, WB Saunders, pp 381–392. Nasisse MP, Davidson MG: Laser surgery in veterinary ophthalmology: perspectives and potential, Semin Vet Med Surg (Small Anim) 3:52–61, 1988. Nadelstein B, Davidson MG, Gilger BC: Pilot study on diode laser iridotomy in dogs, Veterinary and Comparative Ophthalmology 6:230–232, 1996. Nasisse MP, Davidson MG, Olivero DK, et al: Neodymium:YAG laser treatment of primary canine intraocular tumors, Progress in Veterinary and Comparative Ophthalmology 3:152–157, 1993. Rosolen SG, Ganem S, Gross M, et al: Refractive corneal surgery on dogs: preliminary results of keratomileusis using a 193 nanometer excimer laser, Veterinary and Comparative Ophthalmology 5:18–24, 1995. Sapienza JS, Miller TR, Gum GG, et al: Contact transscleral cyclophotocoagulation using a neodymium:yttrium aluminum garnet laser in normal dogs, Progress in Veterinary and Comparative Ophthalmology 2:147–153, 1992. Shieh E, Boldy KL, Garbus J: Excimer laser keratectomy in the treatment of corneal opacities, Progress in Veterinary and Comparative Ophthalmology 2:75–79, 1992. Sullivan TC, Nasisse MP, Davidson MG, et al: Photocoagulation of limbal melanoma in

Further reading dogs and cats: 15 cases (1989–1993), J Am Vet Med Assoc 208:891–894, 1996. Vainisi SJ, Packo KH: Management of giant retinal tears in dogs, J Am Vet Med Assoc 206:491–495, 1995. Whigham HM, Brooks DE, Andrew SA, et al: Treatment of equine glaucoma by transscleral neodymium:yttrium aluminum garnet laser cyclophotocoagulation: a retrospective study of 23 eyes of 16 horses, Vet Ophthalmol 2:243–250, 1999.

Perioperative ophthalmic drugs Gerding P, Essex-Sorlie D, Vasaune S, Yack R: Use of tissue plasminogen activator for intraocular fibrinolysis in dogs, Am J Vet Res 53:894–896, 1992. Gerding PA, McLaughlin SA, Brightman AH, Essex-Sorlie D, Helper LC: Effects of intracameral injection of viscoelastic solutions on intraocular pressure in dogs, Am J Vet Res 50:624–628, 1989. Jampol LM, Jain S, Pudzisz B, Weinreb RN: Nonsteroidal anti-inflammatory drugs and cataract surgery, Arch Ophthalmol 112:891–894, 1994. Johnson RN, Balyeat E, Stern WH: Heparin prophylaxis for intraocular fibrin, Ophthalmology 94:597–601, 1987. Liesegang TJ: Viscoelastic substances in ophthalmology, Surv Ophthalmol 43:268–293, 1990. Martin C, Kaswan R, Gratzek A, Champagne E, Salisbury MA, Ward D: Ocular use of tissue plasminogen activator in companion animals, Progress in Veterinary and Comparative Ophthalmology 3:29–36, 1993. Millichamp NJ, Dziezyc J: Comparison of flunixin meglumine and flurbiprofen for control of ocular irritative response in dogs, Am J Vet Res 52:1452–1455, 1991. Nasisse MP, Cook CS, Harling DE: Response of the canine corneal endothelium to intraocular irrigation with saline solution, balanced salt solution, and balanced salt solution with glutathione, Am J Vet Res 47:2261–2265, 1986. Roze M, Thomas E, Davot JL: Tolfenamic acid in the control of ocular inflammation in the dog: pharmacokinetics and clinical results

obtained in an experimental model, J Small Anim Pract 37:371–375, 1996. Skuta GL: Antifibrotic agents in glaucoma filtering surgery, Int Ophthalmol Clin 33:165–182, 1993. Taylor MM, Kern TJ, Riis RC: Intraocular bacterial contamination in canine cataract surgery, Vet Pathol 29:475, 1992. Ward DA, Ferguson DC, Ward SL, Green K, Kaswan RL: Comparison of the blood– aqueous barrier stabilizing effects of steroidal and nonsteroidal anti-inflammatory agents in the dog, Progress in Veterinary and Comparative Ophthalmology 2:117–124, 1992. Wilkie DA, Willis AM: Viscoelastic materials in veterinary ophthalmology, Vet Ophthalmol 2:147–153, 1999.

Subpalpebral medication Blair MJ, Gionfriddo JR, Polazzi LM, et al: Subconjunctivally implanted microosmotic pumps for continuous ocular treatment in horses, Am J Vet Res 60:1102–1105, 1999. Brooks DE: Use of an indwelling nasolacrimal cannula for the administration of medication to the eye, British Veterinary Journal: Equine Ophthalmology Supplement 2:135–137, 1983. Frauenfelder H, McIlwraith W: Placement of a subpalpebral catheter in a standing horse, Vet Med Small Anim Clin 74:724–728, 1979. Gelatt KN: Postoperative medications in horses and dogs, Vet Med 62:1165–1172, 1967. Gelatt KN: Blepharoplastic procedures in horses, J Am Vet Med Assoc 151:27–44, 1967. Gelatt KN: A modified subpalpebral system for the horse, Journal of Equine Medicine and Surgery 3:141–143, 1979. Gelatt KN, Peterson JE, Myers V, McClure R: Continuous subpalpebral medication in the horse, J Am Anim Hosp Assoc 8:35–37, 1972. Giuliano EA, Maggs DJ, Moore CP, et al: Inferomedial placement of a single-entry subpalpebral lavage tube for treatment of equine eye disease, Vet Ophthalmol 3:153–156, 2000. Martin B, Severin G: Topical medication of the eye using a subpalpebral tube. In Proceedings

of the 14th Annual Meeting of the American Association of Equine Practitioners, 1968, p 324. Myrna KE, Herring IP: Constant rate infusion for topical ocular delivery in horses: a pilot study, Vet Ophthalmol 9:1–6, 2006. Schoster JV: Revisiting ocular lavage systems for the horse. In Proceedings of the 36th Annual Meeting of the American Association of Equine Practitioners, 1990, pp 575–583. Schoster JV: The assembly and placement of ocular lavage systems in horses, Vet Med 87:460–471, 1992. Sweeney CR, Russell GE: Complications associated with use of a one-hole subpalpebral lavage system in horse: 150 cases (1977–1996), J Am Vet Med Assoc 211:1271–1274, 1997. White SL: Construction and placement of a subpalpebral lavage system for medication of the eye. In Proceedings of the 43rd Annual Meeting of the American Association of Equine Practitioners, 1997, pp 160–162. Whitley RD, Lavach JD, Gelatt KN: Subpalpebral lavage system for administering frequent topical medications to the equine eye, Florida Veterinary Journal 8:10–14, 1979.

Restraint Hazra S, De D, Roy B, et al: Use of ketamine, xylazine and diazepam anesthesia with retrobulbar block for phacoemulsification in dogs, Vet Ophthalmol 11:255–260, 2008. Hendrix DVH: Eye examination techniques in horses, Clinical Techniques in Equine Practice 4:2–10, 2005. Lavach DJ, Roberts SM, Severin GA: Current concepts in equine ocular therapeutics, Vet Clin North Am Large Anim Pract 6:435–449, 1984. Rubin LF, Gelatt KN: Analgesia of the eye. In Soma LR, editor: Textbook of Veterinary Anesthesia, Baltimore, 1971, Williams and Wilkins, pp 489–499. Seim HB, Creed JE, Smith KW: Restraint techniques for prevention of self-trauma. In Bojrab MJ, editor: Current Techniques in Small Animal Surgery, ed 3, Philadelphia, 1990, Lea and Febiger, pp 42–49.

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CHAPTER

3

Anesthesia for ophthalmic surgery Kirk N. Gelatt

Chapter contents Introduction

37

Local or regional eyelid injections/nerve blocks

43

Ophthalmic effects of general anesthetics

37

Retrobulbar injections/nerve blocks in animals

44

Preanesthetic medications

39

Injectable general anesthetics

40

Choice of general anesthetic for selected ophthalmic surgical procedures

47

Inhalational general anesthetics

40

Neuromuscular blocking agents

41

ADAPTATIONS FOR LARGE ANIMALS AND SPECIAL SPECIES

47

Ophthalmic drug and anesthetic drug interactions

42

Horse

47

43

Cattle

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Systemic diseases and general anesthesia

Introduction The advances in veterinary anesthesia have paralleled those in veterinary ophthalmic surgery, and have resulted in less anesthetic risk, and improved patient care and management. Studies in different animal species, including humans, suggest frequent similar ophthalmic responses to tranquilizers, narcotic analgesics, dissociative anesthetics, inhalational general anesthetics, and neuromuscular relaxants; however, species differences can occur. Combinations of critical peri-, intra-, and postoperative topical and systemic drugs are common in veterinary ophthalmic patients, and should be accommodated by the choice of general anesthetic agents and protocols. At the same time, concurrent general anesthesia and ophthalmic needs must avoid drug selections that are contraindicated or incompatible when used simultaneously. A significant number of ophthalmic patients are old and may have other diseases that may influence the choice of general anesthetics. In this chapter the impact on the eye and associated structures of drugs administered as part of general anesthesia will be summarized.

Ophthalmic effects of general anesthetics Intraocular pressure Intraocular pressure (IOP) results from a relative equilibrium between aqueous formation, aqueous humor outflow,

and the resistance of the fibrous tunics, e.g., the cornea and sclera, to pressure. The different drugs administered to tranquilize, sedate, and/or anesthetize animals may affect IOP directly by influencing the aqueous humor dynamics, or indirectly by causing hypercapnia, changes in extraocular muscle tone, hypoxemia, and hypothermia. Most general anesthetics lower IOP through actions on the central nervous, respiratory, and circulatory systems. The reduction in IOP is also related directly to the depth of general anesthesia. Most general anesthetics seem to lower IOP by an increase in the rate of aqueous humor outflow. Drugs that directly cause ocular hypotension can also produce ocular hypertension secondary to respiratory depression and acidosis that sometimes occurs with prolonged general anesthesia. As a general observation, drugs that produce an abrupt increase in arterial blood pressure will result in a moderate increase in IOP. This elevation in IOP is usually transient as the aqueous humor dynamics rapidly readjust and return to normal levels of IOP. The major percentage of the resistance of aqueous humor outflow is determined by the episcleral venous pressure. Drugs that produce marked increases in central venous pressure and episcleral venous pressure can also temporarily elevate IOP. The increased central venous pressure may also expand the anterior and posterior uveal vascular beds, indirectly increasing IOP. Expansion of the uveal vascular channels may produce pressure on the vitreous when the globe has been opened, and force the vitreous, its patellar fossa, and even the lens toward the anterior chamber.

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Anesthesia for ophthalmic surgery

Drug-induced changes in extraocular muscle tone can influence IOP. As most animal species have lower scleral rigidity than humans, relaxation of the extraocular and retrobulbar muscles markedly decreases the pressure of these orbital tissues upon the globe. The ketamineassociated elevation in IOP that occurs in humans is thought to be directly related to the increase in extraocular muscle tone. In lightly anesthetized dogs, intravenous administration of succinylcholine can result in a shortterm elevation in IOP. This 5–10 min elevation in IOP is thought to be related to the unusual sensitivity of the extraocular muscles to succinylcholine, and the initial muscle fasciculations that occur during the onset of the drug’s action. When the insertions of the extraocular muscles are severed in the cat, succinylcholine administration does not change IOP. Animals, in general, possess lower ocular rigidity than humans. As a result, when either the cornea or the sclera is incised and IOP released, the entire globe tends to collapse. The sclera in both the dog and cat possesses elastic fibers, in addition to the major complement of collagen, and as a result the sclera lacks rigidity. When the globe is collapsed, corneal and intraocular surgical procedures are more difficult to perform. The level of IOP in animals with low ocular rigidity also enhances the effects of retrobulbar muscle tone. Once the globe has collapsed, extraocular muscle tone may become of greater concern, tending to distort and displace forward the vitreous, lens, and anterior uvea.

Corneal drying and exposure Corneal abrasions, drying of the cornea, conjunctival irritation, and reduced tear formation have been associated with general anesthetics in humans and animals. Ketamine in cats has been associated with corneal drying, although the individual roles of reduced tear formation rates and loss of the protective blink reflex have not been differentiated. Hence, in cats undergoing ketamine anesthesia the corneas should be protected by copious amounts of ophthalmic petroleum-based bland ointment and/or the eyelids closed temporarily by tape. The same applies in dogs, and petroleum-based bland ointment should be applied to both eyes, depending on the type of ophthalmic surgery. The rate of aqueous tear formation in dogs, as determined by Schirmer’s tear test, after combinations of subcutaneous atropine, intravenous thiamylal sodium, and halothane or methoxyflurane was reduced by about 70% within 10 min and by 97% after 60 min. Another study has indicated that subcutaneous atropine reduces Schirmer’s tear test levels in normal dogs by about 55% at 60 min after drug administration. In dogs and cats with reduced levels of tear formation, the administration of parenteral and/or topical atropine can abruptly lower Schirmer’s tear test levels to zero, and initiate the clinical signs of keratoconjunctivitis sicca. Although the topical effects of general anesthetics have not been reported in large and special species animals, petroleum-based bland ointment is applied liberally to protect the corneoconjunctival surfaces during prolonged general anesthesia.

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Oculorespiratory cardiac reflex The oculocardiac or oculorespiratory cardiac reflex was first described by Aschner and Dagnini in 1908 in two simultaneous but independent reports. The afferent aspect of this reflex is carried in the long and short ciliary nerves, the ciliary ganglion, and the ophthalmic branch of the trigeminal nerve via the gasserian ganglion to the trigeminal sensory nucleus. Short internuncial fibers within the reticular formation connect the trigeminal sensory nucleus to the visceral motor nucleus of the vagus nerve and its descending nerve to complete the efferent limb to the heart. The afferent limb of the ophthalmic division of the trigeminal nerve does not appear to be unique. Intraorbital stimulation of the third, fourth, and sixth cranial nerves will also produce consistent respiratory prolongation, but more variable cardiac responses. There appears to be significant species differences for the oculorespiratory cardiac reflex (documented in dogs, cats, horses, and birds), and whether the cardiac, the respiratory, or a combination of both components occurs. In addition to the induced bradycardia, in some species such as the dog, the concurrent respiratory depression can be more profound. The reflex may be initiated by a number of ophthalmic manipulations, including ocular pressure massage for glaucoma, intraorbital injections of local anesthetics (which are also used to block this reflex), surgical traction of the extraocular muscles, and manipulations of the eyelid muscles. In dogs under general anesthesia, neuromuscular blocking agents, and controlled ventilation, only the cardiac portion of this reflex can be appreciated. There may be some individual animal variations relative to the oculorespiratory cardiac reflex in the dog and cat, with only some animals demonstrating this reflex consistently. The primary effect in the cat seems to be respiratory; in the dog, respiratory depression is the dominant response, but bradycardia can develop. To manage the oculorespiratory cardiac reflex, a number of strategies have been developed. To diminish or completely block the vagal effect on the heart, intravenous atropine is the standard treatment. Unfortunately, atropine administration yields inconsistent results. Consequently, the rationale to administer parenteral atropine preoperatively in dogs differs among veterinary anesthesiologists. One school recommends against the routine administration of parenteral atropine preoperatively. If bradycardia develops during the surgical procedure, surgery is temporarily halted and atropine is administered intravenously. Other veterinary anesthesiologists continue to recommend routine use of preoperative parenteral atropine to prevent the potential oculorespiratory cardiac reflex from developing. Unfortunately, intravenous atropine may not only increase the heart rate in the dog, but also increase the possibility of ventricular dysrhythmias. The intravenous dose of atropine to treat and/or prevent the oculorespiratory cardiac reflex in the dog seems critical. In children, although the prophylactic use of parenteral atropine seems to lower the incidence of the oculocardiac reflex, it has also been associated with severe and prolonged ventricular dysrhythmias. Low levels (0.015 mg/kg IV) of atropine in dogs with an experimentally induced oculorespiratory cardiac reflex may actually enhance respiratory depression. Higher doses of

Preanesthetic medications

atropine (0.023–0.04 mg/kg) may eliminate the bradycardia but prolong the apnea. Of these two complications, clinical management of apnea with controlled ventilation is the most feasible solution. An alternative to atropine in the dog is glycopyrrolate (0.01 mg/kg IV, usually given in two divided doses; often the second dose is not necessary) which appears as effective in preventing the oculorespiratory cardiac reflex but produces tachycardia. Under most circumstances, if the oculorespiratory cardiac reflex develops during ophthalmic surgery, surgery is suspended for several minutes and the depth of general anesthesia is increased. Less aggressive surgery is then slowly resumed while the respiratory and cardiac rates are carefully monitored. Fortunately, the onset of the oculorespiratory cardiac reflex is usually in the early aspects of surgery, and in intraocular surgical procedures before critical manipulations have begun.

Eye position During the induction of general anesthesia most injectable and inhalational anesthetics produce a downward and inward rotation of the eye that limits access to the cornea, anterior chamber, and anterior segment. As the globe is rotated ventromedially, the nictitating membrane simultaneously protracts to nearly cover the cornea. Some degree of enophthalmia also develops, decreasing further the exposure of the cornea and globe for surgery. In the large and giant breeds of dogs, access to the eye is already limited, and these drug effects can severely compromise surgical exposure of the eye. This poor positioning of the globe can handicap the surgeon by impairing observation of the entire cornea and anterior segment, increasing the difficulties of surgical manipulations, and unnecessarily prolonging the surgery. Several strategies have been developed to correct the rotation of the globe and exposure difficulties associated with general anesthetics. Unfortunately, most of these remedies to improve exposure may also result in some additional operative risks. Sutures may be placed in the anterior sclera or the rectus muscle insertions, and anchored to the eyelid specula or drapes. Scleral clips may be used similarly. Retrobulbar injections with saline positioned directly into the extraocular muscle cone to push the eye forward, or external to the extraocular muscle cone to turn the globe, may also produce noticeable inward compression of the posterior segment and additional pressure on the vitreous body. The animal cornea and sclera unfortunately lack rigidity, unlike humans and primates in general, and with traction or compression these tunics may become distorted. For certain types of conjunctival and corneal surgery, the distortion of the globe associated with these procedures may be inconsequential. However, when intraocular surgical procedures are planned, any preventable pressure on the globe, in whole or in part, should be avoided. Administration of the different neuromuscular blocking agents has replaced the need for extrabulbar injections to manipulate the position of the globe for surgery.

Pupil size Pupil size has been used historically to monitor the depth of general anesthesia. Without local control by topical mydriatics or miotics, pupil size may vary from marked dilatation to pinpoint in the lighter levels of general anesthesia, to

progressive mydriasis with deep general anesthesia. For conjunctival and corneal surgical procedures, pupil size is often adjusted preoperatively depending upon the concurrent ophthalmic disease. Often the pupil is dilated. Druginduced iridocycloplegia helps reduce the pain associated with preoperative anterior uveitis, and pupil dilatation reduces the likelihood of posterior synechiae formation. In the event of corneal and intraocular surgery, control of pupil size may become critical. Maximum mydriasis is essential for cataract extraction; preoperative pupillary dilatation is usually achieved with 0.3% scopolamine combined with 10% phenylephrine, 1% atropine, or a combination of 1% atropine and 10% phenylephrine. Topical non-steroidal anti-inflammatory agents, such as 0.03% sodium flurbiprofen, can also assist in the maintenance of pupillary dilatation. Prostaglandins appear to be released when the anterior chamber is entered surgically and initiate strong miotic activity. Endocapsular phacoemulsification of canine cataracts requires maximal mydriasis. Without the combination of topical mydriatics, topical and parenteral corticosteroids, and non-steroidal anti-inflammatory agents, the microsurgical refinements and higher success rates for canine cataract surgery would not have been possible.

Extraocular muscular tone The extraocular muscles are well developed in the dog and, in addition to the four rectus and two oblique extraocular muscles, include the retractor oculi muscle that inserts onto the sclera under the rectus muscle insertions and behind the globe’s equator. This bulk of extraocular muscles may produce pressure and indent the posterior segment of the globe, even with optimal general anesthesia. The extraocular muscle pressure, combined with the low scleral rigidity of the dog, seems to be more important once the anterior chamber has been entered, as during cataract and lens removal. If general anesthetics also increase central venous pressure, additional orbital pressure on the globe may develop from the extensive venous plexuses within the orbit. In the cat, the effects of the extraocular muscles during general anesthesia seem less important than in the dog. This may be caused by the poorly developed cat extraocular muscles and the limited orbital space. As a result, increased pressure on the posterior segment is less important and does not appear to be a problem clinically. Several strategies have been developed to address the potential extraocular muscle pressure and its adverse effects when the anterior chamber has been entered surgically. Neuromuscular blocking agents have now become routine for canine and equine intraocular surgery; in addition to greatly reducing extraocular muscle tone, these agents result in optimal eye position for microsurgery.

Preanesthetic medications Preanesthetic medications are designed to facilitate a smooth induction of general anesthesia, and help prevent possible drug-related complications. The controversial routine use of parenteral atropine as an anticholinergic agent has already been discussed. Parenteral glycopyrrolate (0.01 mg/kg IM) is preferred because of fewer cardiac effects.

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Anesthesia for ophthalmic surgery

Sedatives and tranquilizers are often employed preoperatively, especially before intraocular surgery. Both sedatives and tranquilizers lower IOP, probably by increasing the outflow of aqueous humor. Among the phenothiazine tranquilizers, acepromazine maleate is the most frequently recommended. Acepromazine maleate (0.03–0.1 mg/kg IM) is frequently utilized, not only because of the resultant tranquilization, but also for its anti-arrhythmogenic effect associated with the stabilization of the myocardium against catecholamine stimulation and arrhythmogenic agents. The phenothiazine tranquilizers also possess an anti-emetic action perioperatively. Both postoperative vomiting and retching in humans can elevate IOP indirectly by abrupt venous pressure increases. The same effect probably occurs in dogs. Xylazine is not recommended perioperatively in ophthalmic patients because it can cause vomiting and severe bradycardia. Acepromazine may slightly prolong the recovery from general anesthesia, hypothermia, and arterial hypotension, but usually provides a smoother, less traumatic recovery. Most narcotics seem to slightly lower IOP in those animal species studied. The two major advantages of narcotics are that: 1) these drugs are potent analgesics; and 2) they can be chemically antagonized if drug reversal is necessary. Unfortunately, most of these agents except for meperidine are also potent vagotonic and respiratory depressants. Use of narcotic derivatives prior to and following ophthalmic surgery has become more frequent. Occasionally, if the postoperative recovery becomes traumatic, parenteral narcotics are quite effective, probably because of the analgesic effects.

Injectable general anesthetics Most barbiturates lower IOP in animals. This ocular hypotension seems to result from depression of the diencephalon, an increased facility of aqueous humor outflow, and relaxation of the extraocular muscles. Ultrashort-acting barbiturates, such as thiopental and thiamylal (8–12 mg/kg IV) are effective induction agents. The reduction in IOP after administration of these drugs seems to be related to relaxation of the extraocular muscles and an increase in aqueous humor outflow rather than from arterial blood pressure changes. As these agents are potent respiratory depressants, endotracheal intubation should follow immediately after barbiturate administration. Intubation should be standard protocol in all ophthalmic surgical patients. Intermittent and often copious lavage of the corneal and conjunctival surfaces during surgery may exit the nasolacrimal system and accumulate in the mouth and pharynx. Ketamine may be an exception to the rule for injectable anesthetics. Elevated IOP has been associated with ketamine, with increased tone of the extraocular muscles in humans. Ketamine, recommended for the cat, has been reported to either not change or increase IOP in the cat by 10%. Ketamine, used alone, is not recommended for the dog because of its tendency to produce seizures. Ketamine, a dissociative anesthetic, may be injected intramuscularly for the induction of general anesthesia in cats. Ketamine is often combined with diazepam in dogs to reduce the possibility of seizures and produce muscular relaxation. An anticholinergic, such as atropine, is also administered to

40

minimize salivation. After general anesthesia is sufficiently deep to permit intubation, general inhalational anesthesia may be initiated for longer duration surgeries. There are other injectable agents that are now used as induction agents for small animals, and experiences with some of these agents, such as propofol, midazolam, and TelazolW, have been excellent. Propofol, as an induction agent, has a recommended intravenous dose in small animals of 6 mg/kg, and then to effect, and has largely replaced the barbiturates. After rapid, smooth and excitement-free onset of general anesthesia, the duration is also relatively short (range 2.5–9 min). Usually administered as a slow bolus injection (to avoid apnea) for the induction of inhalational anesthesia, propofol can be injected repeatedly; however, its short duration of effect requires several injections for relatively short periods of time. Recovery after propofol is usually very rapid, and excitement free. Propofol is thought to lower IOP. Propofol has become the preferred induction agent world-wide in small animals, and the sole general anesthetic for many short-term ophthalmic procedures. Propofol (2,6-diisopropylphenol) is only soluble in water, and is mixed immediately before use. It comes in sterile glass ampoules and without preservatives. It fits a twocompartment open model, with rapid distribution from the plasma into the tissues and rapid metabolic clearance from plasma. It is metabolized by conjugation primarily by the liver and kidney. It is administered as an intravenous bolus at doses that range from 2.5 mg/kg (sedated dog) to 8 mg/kg (unsedated dog) to allow tracheal intubation and the initiation of inhalational anesthesia. Propofol’s anesthesia is quite brief; in unsedated dogs recovery is only 15 min. Propofol can also be used for the maintenance of anesthesia administered by continuous infusion or intermittent bolus. Propofol has minimal analgesic effects, and drugs with analgesic effects, such as opiates, should be administered concurrently. Propofol lowers IOP in humans, and this effect has also been reported in dogs (a decline of 26%). Midazolam is a water-soluble benzodiazepine. It does not induce anesthesia when used alone; hence midazolam is often combined with ketamine, or one of the ultrashortacting thiobarbiturates (thiamylal or thiopental) to induce general anesthesia. TelazolW consists of equal parts of a dissociative agent, tiletamine, and a benzodiazepine, zolazepam. Once in solution, TelazolW has a limited shelf-life of 4 days at room temperature and 14 days at 4 C. The recommended dose for dogs is 6.6–13.2 mg/kg IM or SC, and for cats 9.7– 15.8 mg/kg IM or SC. After deep intramuscular injection of TelazolW, onset of anesthesia is within 2–5 min and the recovery to walking requires 3–5 h. Induction of anesthesia with TelazolW is usually smooth, but recovery can be traumatic.

Inhalational general anesthetics All of the available inhalational general anesthetics lower IOP. The extent of ocular hypotension is directly related to the depth of general anesthesia. The lowering of IOP after inhalational anesthetics seems to result from collective drug actions on the respiratory, circulatory, and central nervous systems. The changes in arterial pressure associated with inhalational anesthetics do not seem to lower the IOP per se, but central venous pressure can be important. Changes

Neuromuscular blocking agents

Neuromuscular blocking agents Neuromuscular blocking agents have recently been added to the general anesthetic protocol for ophthalmic patients to improve exposure of the cornea and eye during intraocular surgery. Administration of neuromuscular blocking agents in dogs produces relaxation of all of the extraocular muscles, and within 30–60 s causes the eye to return to its normal axis from the ventromedial deviation associated with most general anesthetic agents (Fig. 3.1). In cats administered succinylcholine, the globe may assume a superolateral divergent position. Neuromuscular blocking agents have the potential to influence IOP depending on their mechanism of action. In humans, d-tubocurarine lowers IOP by relaxation of the extraocular muscles; however, if the patient hypoventilates,

A

B Fig. 3.1 Position of the canine eye under general anesthesia (a) before and (b) after the administration of neuromuscular blocking agents. Note the improved exposure of the cornea and globe.

leading to hypercarbia and hypoxemia, IOP may increase. In contrast, succinylcholine administered intravenously can elevate IOP in several animal species including the dog and cat (Fig. 3.2). The transient increase in IOP occurs almost immediately after succinylcholine administration, and appears to be directly associated with initial contraction of the extraocular muscles during the depolarization process. In humans, reported sensations after administration of succinylcholine include a feeling of increased orbital pressure, vertigo, and diplopia. The effect on IOP by parenteral succinylcholine is influenced by the level of general anesthesia at the time succinylcholine is administered. In unanesthetized persons, the average elevation of IOP after succinylcholine administration was 15 mm Hg. In light levels of general anesthesia after succinylcholine administration, IOP is usually increased 2–4 min later; during deep general anesthesia IOP is not affected. The period for drugrelated elevation in IOP is usually 5–6 min. 50

Effect of succinylcholine on IOP in the dog

40 IOP (mmHg)

in blood gases and the methods of ventilation may also influence IOP. Some of these agents may also lower IOP by increasing the facility of aqueous humor outflow. Prolonged general anesthesia with changes in blood pH and other complications may actually increase IOP. For instance, experiments in dogs with increased inspired CO2 indicate that IOP may rise after initial depression. Hypoventilation that leads to hypercapnia and hypoxemia can eventually result in elevation of IOP. Although some species differences may be present, the reduction in IOP after inhalational general anesthetics may be substantial. Methoxyflurane in humans can lower IOP by 15–25%. Halothane-induced ocular hypotension in children may be of greater magnitude in glaucomatous eyes than in normal eyes, but with more variability. Methoxyflurane in dogs presented for cataract surgery lowers IOP an average of 11 mm Hg with a range of 5–20 mm Hg. Isoflurane is the most frequently used inhalational general anesthetic for veterinary ophthalmic surgery (dog, cat, and horse most frequently), and has largely replaced halothane during the last decade. Halothane produces rapid induction and recovery associated with dose-related depression of the central nervous system. When combined with preanesthetics, such as acepromazine, the need for halothane is reduced. Halothane produces more depression of cardiac function than methoxyflurane, and causes more cardiac dysrhythmias than isoflurane. Halothane causes higher cardiac sensitivity to catecholamines; lidocaine (2–4 mg/kg IV in dogs and 1–2 mg/kg IV in cats) can be used to treat these arrhythmias. If adrenaline (epinephrine) is planned for hemostasis during ophthalmic surgery, isoflurane should be selected over halothane. Halothane is a poor analgesic, and is usually combined with nitrous oxide. Isoflurane is now preferred to halothane. The drug is nonflammable at anesthetic concentrations, is highly stable, and is not broken down by sunlight. Isoflurane has a faster onset of action and recovery because of its low blood solubility. Like halothane, isoflurane depresses cardiovascular function in a dose-dependent manner, but is less arrhythmogenic than halothane. Isoflurane may be used in patients with hepatic disease because it is minimally metabolized by the liver. At this time, isoflurane is recommended as the general anesthetic of choice for most aged and debilitated small animal patients. Sevoflurane is also becoming popular in many veterinary practices world-wide.

Drug 30 20

Control

10 0

0:00 0:01 0:02 0:03 0:04 0:05 0:06 0:07 0:08 0:09 0:10 Minutes n = 5 eyes

Fig. 3.2 The effect of IV succinylcholine on intraocular pressure (IOP) (mm Hg) in dogs under light general anesthesia.

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Anesthesia for ophthalmic surgery

Studies in normal cats suggest that succinylcholine not only elevates IOP an average of 10–12 mm Hg, but also causes a forward displacement of the lens and iris when the anterior chamber is open. In an extracapsular cataract extraction, any forward displacement of the iris, lens, and presumably the vitreous is a cause for concern. If this effect occurs during the latter part of extracapsular cataract extraction, the thin posterior lens capsule is a weak barrier to increased pressure generated with the vitreous body. While succinylcholine acts as a depolarizing neuromuscular agent, members of the non-depolarizing relaxants, including d-tubocurarine, gallamine triethiodide, and pancuronium bromide, have not been associated with a drug-related elevation in IOP. Newer neuromuscular blocking agents used clinically, such as pancuronium bromide, vecuronium, and atracurium besylate, have shorter dose-related effects (Table 3.1). As inactivation of these neuromuscular blocking agents depends on the patient’s plasma anticholinesterases, concurrent use of potent topical anticholinesterase miotics in glaucomatous patients, such as echothiophate iodide and demecarium bromide, is contraindicated. Drugs available for reversal of these neuromuscular relaxants include edrophonium, neostigmine, and pyridostigmine. The neuromuscular blocking agents include atracurium, pancuronium, alcurium, and vecuronium. Atracurium besylate has minimal cardiovascular effects at recommended doses, has a relatively short duration of action without apparent cumulative effects, and elimination is independent of liver and kidney function. An intravenous bolus of atracurium (0.25 mg/kg), injected over 1 min, usually provides paralysis of the dog for about 30 min. For an additional intravenous bolus of atracurium, the dosage is reduced to 0.15 mg/kg. Atracurium can be antagonized, if necessary, with intravenous edrophonium at a dose of 0.5 mg/kg. Bradycardia has been associated with edrophonium administration. Either atropine administered previously or the very slow injection of edrophonium minimizes this effect. Neostigmine (2.5 mg), combined with atropine (1.2 mg), can also be used intravenously to antagonize the effects of atracurium. The total dose of neostigmine should not exceed 0.1 mg/kg. Pancuronium bromide is another frequently used neuromuscular blocking agent for canine intraocular surgery. An intravenous injection of pancuronium (0.06 mg/kg) causes a maximum neuromuscular blockage of 3–5 min that produces skeletal muscle relaxation and apnea for about 40 min. However, these muscle relaxants are not anesthetics. For their proper use, the patient’s respiration is carefully controlled by mechanical ventilation, neuromuscular and cardiovascular functions are adequately monitored, and the Table 3.1 Doses and length of paralysis with non-depolarizing neuromuscular blocking agents in dogs

42

Drug

IV dose (mg/kg)

Length of effect (min)

Atracurium

0.5

15–80

Alcurium

0.06–0.1

30–40

Pancuronium

0.06–0.1

20–40

Vecuronium

0.06–0.1

15–20

inhalational general anesthetic is administered at sufficient levels to maintain unconsciousness and analgesia. Without adequate ventilation, these agents may cause respiratory acidosis within as short a time as 5 min. Most general anesthetics cause a ventromedial rotation of the globe, and local attempts to improve exposure of the eye have significant limitations and complications. After the administration of neuromuscular relaxants, the globe position returns to normal, permitting optimum surgical exposure, and IOP appears low. With pancuronium (0.06 mg/kg IV), the ocular changes persist for about 20–30 min following drug administration. The relaxation of the extraocular muscles releases the normal pressure on the globe, and the forward displacement of the vitreous, lens, and anterior uvea is minimal. Use of these neuromuscular blocking agents may contribute directly to improved cataract surgery results in dogs. Once the anterior chamber is surgically entered, and the majority of the cataract removed via extracapsular extraction or phacoemulsification, the forward displacement or central protrusion of the posterior lens capsule within the pupil is reduced as much as possible (Fig. 3.3). With reduced vitreous pressure on the posterior lens capsule, posterior lens capsule tears during surgery are kept to a minimum. Neuromuscular blocking agents that provide about 20– 40 min of muscle relaxation are the most useful (see Table 3.1). These agents are usually administered just before the anterior chamber is entered, and should provide extraocular muscle relaxation for the duration that the anterior chamber is open, the lens is delivered, and most if not all of the time for the apposition of the corneal or limbal wound. If an additional dose is necessary, as with bilateral cataract surgeries, the second dose of neuromuscular blocking agent is usually reduced by one-half.

Ophthalmic drug and anesthetic drug interactions Sometimes the ophthalmic medications and drugs associated with general anesthesia have possible conflicts. For instance, the preoperative treatment of the eye may involve a topical cholinergic miotic, but the anesthetic protocol includes the administration of parenteral anticholinergic agents, such as atropine. Fortunately, the effects of topical ophthalmic drugs are usually predominant because of the systemic dilution that occurs with parenteral drugs. For instance, studies indicate that parenteral glycopyrrolate (0.01 mg/kg IM) in normal dogs does not have any effect on IOP and pupil size. Parenteral atropine and glycopyrrolate at the recommended clinical doses in dogs with glaucoma do not elevate IOP. Other ophthalmic drugs may impact the management of the patient about to be anesthetized. Systemic carbonic anhydrase inhibitors are administered to lower IOP, but can produce a temporary metabolic acidosis and considerable diuresis. Anticholinesterase miotics used for the treatment of glaucoma can reduce the levels of plasma and red blood cell cholinesterases, rendering the patient more sensitive to the neuromuscular blocking agents and causing a prolonged effect. Fortunately, use of miotics for the treatment of glaucoma has become infrequent, and generally replaced by the prostaglandins.

Local or regional eyelid injections/nerve blocks

Fig. 3.3 Effects of extraocular muscle tone during general anesthesia on the posterior lens capsule (a) after extracapsular cataract removal. (b) Changes in the posterior lens capsule after the administration of neuromuscular blocking agents.

A

B

Hyperosmotic agents, such as mannitol and glycerol, are used in veterinary ophthalmology for short-term reduction of IOP, and to reduce the size of the vitreous body preoperatively. In patients with cardiac and pulmonary disease, acute increases in vascular volume associated with hyperosmotic agents may be highly significant. Topical sympathomimetic agents, such as 2% adrenaline (epinephrine) and 10% phenylepinephrine, are important to the veterinary ophthalmologist for their effect on IOP and as mydriatics. Adrenaline (epinephrine) may also be injected (1:10 000 to 1:100 000 concentrations) into the anterior chamber for mydriasis, and to control iridal hemorrhage. Use of halothane as the general anesthetic with these adrenergic agents is associated with occasional extrasystoles and arrhythmias, because the myocardium has been sensitized to these catecholamines. Selection of isoflurane as the general anesthetic for these patients is recommended.

Systemic diseases and general anesthesia Many ophthalmic surgical candidates may have certain systemic diseases that potentially can affect the choice of general anesthesia, the duration of general anesthesia, and the administration of other drugs. In cataract surgery in dogs, animals with diabetes mellitus are the second largest group of patients following those with inherited cataracts. In fact, cataract secondary to diabetes mellitus is the most frequent type of metabolic cataract in the dog and the second most frequent cataract surgery in America. Successful clinical management of the diabetic dog with cataract must not only accommodate the daily control of blood glucose levels, but also control the lens-induced uveitis for optimal success rates after cataract removal. One strategy in diabetic dogs is to substitute aspirin for systemic prednisolone. Topical antiprostaglandins can also reduce the dosage for systemic corticosteroids as well as antiprostaglandins, such as carprofen (RimadylW; Pfizer Animal Health, Exton, PA) and flunixin meglumine (BanamineW; Schering-Plough, Kenilworth, NJ). Administration of topical corticosteroids and even systemic prednisolone may be necessary in some diabetic dogs for treatment of lens-induced uveitis after cataract surgery. Some elevation of blood glucose levels may occur with both topical and systemic corticosteroids in postoperative diabetic dogs. Maintenance of preoperative levels of insulin

doses is usually best in these dogs, until the topical and/or systemic levels of corticosteroids can be reduced or eliminated. Oral glycerin to lower IOP and reduce the vitreous space is not recommended in diabetic dogs as the glycerin is converted to blood glucose. Intravenous mannitol does not elevate blood glucose, and is the recommended systemic osmotic agent for the dog and cat. Systemic hypertension occurs mainly in older dogs and cats, and its presence can complicate intraocular surgery as well as potentially contribute to postoperative intraocular hemorrhage and retinal detachments. The development of these sequelae following apparent successful cataract surgery with an intact corneal or corneoscleral incision should necessitate periodic monitoring of blood pressure. Clinical management of these complications must include successful treatment of the systemic hypertension. Dogs with advanced renal, cardiovascular, and hepatic diseases are not usually candidates for elective intraocular surgeries. Unless these diseases are successfully treated and the animals’ life span significantly increased, the risks and costs of general anesthesia and time for surgery generally negate elective intraocular surgeries in these patients.

Local or regional eyelid injections/ nerve blocks Eyelid injections are used more often in large animals than in small animals for eyelid akinesia, but not local anesthesia, and are targeted at the palpebral nerve and its branches as it extends forward to innervate the orbicularis oculi muscle, the powerful sphincter muscle that closes the upper and lower eyelids. In general, as these palpebral nerve blocks are placed closer to the palpebral fissure, the effects are more localized as the main nerve trunk branches into numerous smaller nerves. Often topical anesthetics are instilled along with eyelid nerve blocks to provide surface anesthesia and permit detailed ophthalmic examinations, subconjunctival injections, collection of samples from the cornea and conjunctiva for cytology or culture, applanation tonometry, and other minimally invasive procedures. The exception in the horse is the supraorbital nerve block, in which local anesthetic is injected at the supraorbital foramen, which provides both mid upper lid akinesia and local anesthesia. Local ophthalmic nerve blocks in large animals

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Anesthesia for ophthalmic surgery

are used for ophthalmic examinations, especially in the horse, and as an adjunct for local or general anesthesia as part of eyelid, orbital or ocular surgery.

Eyelid injections/nerve blocks in the dog Eyelid injections are used in the dog both for eye examination in dogs with very painful ophthalmic disorders, as well as for therapy. Spastic entropion in the dog, a relatively rare condition, may also benefit immediately from the palpebral nerve block. For akinesia of the dog eyelid, local anesthetic (1–3 mL) may be injected subcutaneously along the upper zygomatic arch at its most lateral position or approximately 1–2 cm posterior to the lateral canthus (Fig. 3.4). An effective anesthetic block is demonstrated by drooping of the upper eyelid, an inability to close the palpebral fissure with a fixed and relaxed orbicularis oculi muscle, and an everted lower eyelid. The dog continues to have complete sensitization of the cornea, conjunctivae, and lid surfaces, as well as ocular mobility, and topical anesthetics are usually also instilled to permit minimally invasive diagnostic and therapeutic procedures.

Eyelid injections/nerve blocks in the cat Eyelid injections have not been reported in the cat, but the palpebral nerve pathway in this species is similar to that of other carnivores.

Eyelid injections/nerve blocks in the horse Because the horse’s orbicularis oculi muscle is very powerful, eyelid closure can occur during an eye examination as well as during drug administration in spite of manual efforts by the veterinarian or owner to maintain the palpebral fissure open. As a result, eyelid nerve blocks for akinesia, as well as combined akinesia–anesthesia nerve blocks, are available and used very frequently in the horse (Fig. 3.5).

Fig. 3.5 To perform the palpebral nerve block in the horse, local anesthetic is injected subcutaneously at the highest projection of the zygomatic arch (palpebral nerve only – A), in the groove immediately caudal of the zygomatic arch (B – contains the auriculopalpebral nerve, artery, and vein), or in the supraorbital fossa within the supraorbital process of the frontal bone (C). The first two nerve blocks provide only lid akinesia while the supraorbital nerve block provides both akinesia and analgesia of the mid upper eyelid.

Two different palpebral nerve blocks are frequently used in the horse to produce eyelid akinesia. The most popular is injection of about 1–3 mL of local anesthetic subcutaneously at the highest point of the zygomatic arch, midway in the arch. In the second method, 1–3 mL of local anesthetic is injected in the depression or groove of the ventral edge of the temporal portion of the zygomatic arch, just caudal to the posterior ramus of the mandible. Just before injection of local anesthetic, aspiration is used to check the needle position and avoid injection into the rostral auricular artery or vein. As this nerve block is close to the main trunk of the auriculopalpebral nerve, occasionally more extensive facial nerve block effects may occur, including muscle block effects down to the nostril, as well as a drooping and immobile ear. Topical anesthetic is also instilled for surface anesthesia of the cornea and conjunctiva. The combined akinesia and local analgesia (anesthesia) supraorbital nerve block in the horse is used for diseases localized to the mid upper eyelid. Between 2 and 4 mL of local anesthetic is injected about the supraorbital foramen within the supraorbital arch. Topical anesthetic is also instilled for surface anesthesia of the cornea and conjunctiva.

Eyelid injections/nerve blocks in the cow Eyelid injections in cattle are usually combined with retrobulbar nerve blocks which provide orbital and ophthalmic akinesia and analgesia (anesthesia) during orbital and eyelid surgery. Local anesthetic (2–4 mL) is injected just caudal of the lateral canthus to block the terminal branches of the palpebral nerve.

Retrobulbar injections/nerve blocks in animals

Fig. 3.4 For the palpebral nerve block in the dog, the local anesthetic injection is positioned either immediately above the most lateral projection of the zygomatic arch or about 1–2 cm from the lateral canthus.

44

In non-primates the lateral and part of the caudal floor of the bony orbit is usually open and devoid of bony walls. These areas, consisting of fascial tissue (periorbita), muscles, and blood vessels, and covered with either skin or mucosa, represent potential entry sites for access to the orbital tissues and the injection of drugs. In non-human primate species,

Retrobulbar injections/nerve blocks in animals

orbital access is generally limited to the frontal approach around the intact globe.

Retrobulbar injections/nerve blocks in dogs Access to the cornea and anterior globe may present exposure problems in small animals, especially in certain breeds of dogs. Fortunately, the lateral and dorsolateral aspects of the dog orbit are incomplete, and accommodate retrobulbar injections. Injections of sterile 0.9% saline can enhance the presentation of the cornea and globe, but only with some risk. The injection is performed with the dog under general anesthesia with the objective of forcing the globe further rostrad in the orbit, or to turn the globe and improve exposure of a selected area of the cornea and/or anterior segment. Providing retrobulbar anesthesia is another consideration. The amount of sterile saline injected is ascertained as the injection is performed, and the response of the globe to the space-occupying solution is assessed. The hypodermic needle may be inserted caudal to the junction of the lateral orbital ligament and dorsal aspects of the zygomatic arch (Fig. 3.6). The needle is directed towards the retrobulbar space in a ventromedial direction toward the opposite mandibular joint. The solution may be injected in the lateral aspects of the extraocular muscle cone, or immediately caudal to the globe and within the retrobulbar muscle mass. Injections external to the retrobulbar muscle cone will rotate the globe laterally; injections immediately behind the globe will push the globe forward. The volume injected should be limited to produce the desired outcome, but not result in undue pressure and distortion of the globe. Another injection site is ventral to the anterior zygomatic arch and rostrad to the vertical portion of the ramus of the mandible, the Barth’s nerve block (Fig. 3.7). The hypodermic needle, after passing the ramus of the mandible, is directed

Fig. 3.7 Barth’s method for retrobulbar injection in the dog consists of placement of a 5–8 cm, 22 g hypodermic needle inserted beneath the zygomatic arch at the level of the lateral canthus. The needle must pass rostrad to the vertical portion of the ramus of the mandible and directed to the orbital fissure.

toward the orbital fissure. Injections external to the retrobulbar muscle cone in the orbital floor and the medial orbit wall are possible with this method, and can be used to shift the globe dorsally. Retrobulbar injections can also be performed with curved, 5 cm long hypodermic needles directed through the conjunctiva or the eyelids to deposit solution beside or caudal to the globe (Dietz’s method). The volume and position of the injection within the orbit will shift the eye accordingly.

Retrobulbar injections/nerve blocks in cats Retrobulbar injections in the cat are not recommended because of the limited retrobulbar space and difficulty in proper positioning of the injection.

Retrobulbar injections/nerve blocks in horses

Fig. 3.6 Retrobulbar injections can be positioned in the dog with an 8 cm, 22 g hypodermic needle inserted caudal to the lateral orbital ligament and directed toward the opposite mandibular joint. Because the dog lacks ocular rigidity, extraocular injections that are several milliliters can indent the globe. Injections within the extraocular muscle cone may have greater effects than those injected next to the orbital walls.

Retrobulbar local anesthetic injections have been described in the horse by Berge and Lichenstern. The posterior orbit and entry of the critical cranial nerves in the horse are about as deep as in cattle (10–12 cm), but the posterior orbit is more conical. With gas inhalation general anesthesia, and often neuromuscular blocking agents and forced ventilation, retrobulbar nerve blocks in the horse are unnecessary and redundant. In the Berge method, an 8–10 cm, 18 g needle is inserted caudal to the supraorbital process of the frontal bone near the supraorbital foramen. The long needle is directed ventromedial (about 40 from the vertical) and slightly caudal toward the area of the orbital fissure where 15–20 mL of local anesthetic is injected (Fig. 3.8). In a modification of the Berge technique, in the Lichenstern’s method, an 8–10 cm, 18 g needle is inserted 1.5 cm caudal to the middle of the supraorbital process. The needle is directed toward the opposite last upper premolar tooth. The taut extraocular muscles’ fascial cone may be felt as

45

3

Anesthesia for ophthalmic surgery

combined with neuromuscular blocking agents is highly recommended.

Retrobulbar injections/nerve blocks in cattle

Fig. 3.8 In Berge’s retrobulbar nerve block in the horse for injection within the orbital fissure, the needle is inserted behind the supraorbital foramen of the dorsal orbital rim, inclined 40 to the vertical, and directed medioventrally and somewhat caudally.

the needle penetrates it. Approximately 20 mL of local anesthetic is injected near the orbital fissure. As a third method, the lateral and medial canthal routes may be used to inject about 10–15 mL of local anesthetic at each site. Of the large animal species, intraocular surgery is performed most often in the horse. As this species has considerable high scleral elasticity (low scleral rigidity), sizeable volume retrobulbar injections can markedly indent the posterior segment (as viewed by ophthalmoscopy), and increase the likelihood of vitreous prolapse and posterior lens capsule rupture during cataract surgery. Therefore, when intraocular surgery is considered in this species, general gas anesthesia

A

Because of inherent problems associated with general anesthesia in cattle, as well as economics, regional nerve blocks are common in this species. In fact, most orbital, eyelid, conjunctival, and corneal surgery is performed with regional injectable anesthesia. Of the three different routes for orbital injections of regional anesthesia in the cow, i.e., Peterson’s, Schreiber’s, and Hare’s, Peterson’s is the most common in America, but somewhat more difficult. A relatively simple method in cattle, the four-point block, uses more local anesthetic than the Peterson method, and delivers retrobulbar anesthetic through the dorsal, medial, lateral, and ventral conjunctival fornices directly into the retrobulbar space. In Peterson’s regional nerve block, an 8–10 cm, 18–20 g slightly curved hypodermic needle is inserted at the posterior angle of the zygomatic arch and lateral orbital rim, and directed anterior of the coronoid process of the mandible and inferomedially to the pterygopalatine fossa near the foramen orbitorotundum (Fig. 3.9). After aspiration (avoiding the internal maxillary artery), 15–20 mL of local anesthetic is injected. The auriculopalpebral nerve is blocked by placing 3–5 mL of local anesthetic subcutaneously along the dorsal zygomatic arch. Successful nerve blocks result in mydriasis, lack of globe mobility, loss of corneal sensation, and loss of eyelid movement. The globe in some cows can be proptosed moderately, and maintained in position by the eyelids.

Complications of retrobulbar injections/ nerve blocks Retrobulbar injections require care, and can induce retrobulbar hemorrhage. Hence, after needle placement and before injection, aspiration is attempted to minimize injection into the ocular vasculature. The animal orbit contains large veins

B

Fig. 3.9 In the Peterson retrobulbar nerve block in cattle: (a) View from side of orbit: A slightly curved, 10 cm hypodermic needle is inserted in the caudal angle (arrow) of the supraorbital process and zygomatic arch, and manipulated in front of the coronoid process of the mandible. (b) Frontal view: The hypodermic needle is then directed medial and somewhat ventrally to enter the floor of the pterygopalatine fossa and the orbitorotundum foramen (arrow). After aspiration to make certain the maxillary artery has not been entered, approximately 15–20 mL of local anesthetic is injected. As the hypodermic needle is withdrawn, an additional 3–5 mL of local anesthetic is injected subcutaneously for akinesia of the eyelids.

46

Horse

and venous plexuses, but hemorrhage sufficient to produce additional pressure of the globe, and even enter the subconjunctival spaces, fortunately occurs infrequently. If this occurs, surgery should be delayed until the hemorrhage has reabsorbed. Inadvertent puncture of the globe with the needle is rare, but a serious complication. The retrobulbar saline is usually reabsorbed within 30–60 min. With the use of intravenous neuromuscular blocking drugs, use of retrobulbar injections to manipulate the globe is less common and may be redundant. A few cases of cattle have been reported to suffer respiratory collapse and sudden death after the Peterson retrobulbar block, presumably from accidental anesthetic injection within the optic nerve meninges or the cerebrospinal space.

Choice of general anesthetic for selected ophthalmic surgical procedures The ophthalmic surgical procedure may influence the choice of induction agent and general anesthetic based on the expected duration of the surgery, and the level of pain and discomfort expected postoperatively.

Orbital surgery Orbital surgery is expected to result in some blood loss, and excessive globe traction may initiate the oculorespiratory cardiac reflex. In small animals, a combination of injectable and inhalational anesthetics is used to provide general anesthesia for about 60 min. The administration of acepromazine preoperatively will usually assist in promoting a smooth recovery.

Eyelid surgery Surgical procedures of the eyelids usually require induction with injectable anesthetics and continued general anesthesia with inhalational agents. Occasionally multiple administrations of only injectable anesthetics will suffice. In very young puppies with entropion, correction with the ‘tacking procedure’ often uses halothane anesthesia induced via mask.

Nasolacrimal flush and catheterization Only topical anesthesia (occasionally combined with acepromazine tranquilization, or in non-cooperative patients) is necessary for many of the manipulations required for the nasolacrimal system, including flushes, catheterization, and incisions to open the imperforate lacrimal punctum.

Conjunctival and nictitating membrane surgeries To perform nictitating membrane flaps and small eyelid or conjunctival tumor removals in small animals, propofol in dogs and cats, or ketamine in cats, is recommended. For conjunctival grafts, the time taken to perform these procedures is about 30–60 min. As a result, induction with a shortacting intravenous barbiturate, endotracheal intubation, and maintenance with inhalational anesthesia is recommended.

A smooth recovery is necessary, and usually an analgesic, such as butorphanol tartrate, is indicated.

Corneal and intraocular surgeries For corneal and intraocular surgical procedures, tranquilization with acepromazine, propofol for induction, and inhalation agents for maintenance of general anesthesia are recommended. The administration of neuromuscular blocking agents (such as pancuronium 0.06 mg/kg IV) is initiated once general anesthesia is stabilized and a few minutes before entry into the anterior chamber is achieved. Both a smooth onset and recovery from general anesthesia are anticipated. Some degree of analgesia is usually necessary during the immediate postoperative period, and often butorphanol tartrate or a similar drug is administered.

Recovery from general anesthesia During the recovery period after ophthalmic surgery, the patient should slowly and smoothly recover from general anesthesia. Excessive whining, yelping, barking, vomiting, and uncoordinated movement and thrashing are to be avoided. These effects may threaten the integrity of the surgical wounds and can result in trauma and swelling of the eyelids, subconjunctival hemorrhages, hyphema, and anterior uveitis. The optimum clinical management of these complications is to prevent their occurrence by the appropriate selection of perioperative drugs and general anesthetics. Tranquilizers, such as acepromazine, have a reasonably long duration of action, and this effect usually includes the critical postoperative period. The usual dosage for acepromazine is 0.03– 0.1 mg/kg administered intramuscularly or subcutaneously about 15 min before ophthalmic surgery. The lower dosage level is best for older canine patients; the higher dosage level is recommended for young, healthy, and excitable patients. Butorphanol tartrate, an opiate agonist/antagonist analgesic with strong antitussive activity, may also be administered postoperatively (0.5–1.0 mg/kg SC) to promote a smooth recovery from general anesthesia. Restraint devices, such as the Elizabethan collar, hobbles, and bandaging of the front paws, are additional measures that can protect the eye during the recovery phase from general anesthesia.

ADAPTATIONS FOR LARGE ANIMALS AND SPECIAL SPECIES

Horse The introduction of many drugs for sedation, analgesia, and restraint in large animals, especially the horse, has advanced significantly in the past 40 years. In the 1960s, sedation of horses for eye examination or minor invasive procedures involved only acepromazine, and was not very satisfactory. The introduction of xylazine in the 1970s, used singly or best combined with acepromazine, provided much improved sedation and adequate restraint for detailed ophthalmic examinations in horses with considerable

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Anesthesia for ophthalmic surgery

eye-related pain, as well as more invasive procedures (corneal cytology, nasolacrimal system cannulation, etc.). Nowadays, the availability of detomidine combined with butorphanol (introduced in the 1990s) provides deep sedation and the best possible restraint. In ranking available drugs for sedation and restraint in the horse, we would rank (from lowest to highest sedation):

• • • •

acepromazine (0.02–0.05 mg/kg IV; avoid in stallions because of the potential for priapism) xylazine (usual dose: 0.2–0.4 mg/kg IV) xylazine (0.6 mg/kg IV) combined with acepromazine (0.02 mg/kg IV) detomidine (our dose is 0.005–0.012 mg for an ophthalmic examination rather than the recommended 0.01–0.02 mg/kg used for pain or placing a lavage system) combined with butorphanol (0.02–0.03 mg/kg IV).

Probably most, if not all, sedatives lower IOP in horses. Acepromazine and xylazine lower IOP in horses by about 10–20%. Both xylazine and detomidine are a2-agonist sedatives. IOP decline seems secondary to venous pressure, direct pressure on the globe, blood pressure, tone in the extraocular muscles, head position, and the rate, dose, and rapidity of drug administration. Decline in IOP secondary to lower systemic blood pressures is the likely explanation. Intravenous xylazine at dosages of 0.3 mg/kg (23%), 1.0 mg/kg (27%), and 1.1 mg/kg combined with ketamine (2.2 mg/kg), lower IOP. The majority of ophthalmic surgeries performed in horses use general anesthesia, and for corneal surgery often involving penetrating corneal wounds, as well as surgery of the iris, lens, and cataracts, and neuromuscular paralysis for optimal globe positioning and ocular hypotony. However, general anesthesia is not without risk in the horse! Smooth recovery does not always occur in a horse coming out of general anesthesia, and a smooth recovery is hopefully

characterized by a horse which stands on its first attempt, and does not repeatedly struggle to stand and fall! Unsatisfactory and prolonged recoveries risk injury to the eye and limbs and other serious mishaps. Mortality with general anesthesia in the horse has been reported as 1.9%, and excluding those horses with emergency abdominal procedures, the death rate is 0.9%. Although complications with general anesthesia in horses undergoing ophthalmic surgery have not been reported, fatalities after ear, nose, and throat (ENT) procedures have been reported as 0.88%. As the length of time for the ophthalmic surgical procedure and general anesthesia increases, the likelihood of complications also increases. Fortunately, most ophthalmic procedures in the horse take less than 1 h, or perhaps slightly more! Standing ophthalmic procedures, including standing enucleation, have been reported in horses. Most equine standing surgeries are relatively minor; however, some may become too difficult, requiring use of general anesthesia for successful completion.

Cattle Cattle are most often physically restrained using its stanchion (dairy cattle) or a squeeze chute and variable head restraint (beef cattle). Sedation is generally not employed because of the bovine’s very high sensitivity to drugs, such as xylazine, and must be carefully administered. The recommended dose (see Plumb’s Veterinary Drug Handbook) is 0.05–0.15 mg/kg IV or 0.10–0.33 mg/kg IM. Pretreatment with atropine can decrease the bradycardia and hypersalivation. Xylazine should be avoided in pregnant cattle (last trimester) and in animals that are dehydrated, have urinary tract obstructions, or are debilitated.

Further reading General Auer U, Mosing M, Moens YPS: The effect of low dose rocuronium on globe position, muscle relaxation, and ventilation in dogs: a clinical study, Vet Ophthalmol 10:295–298, 2007. Brunson DB: Anesthesia in ophthalmic surgery, Vet Clin North Am Small Anim Pract 10:481–495, 1980. Gelatt KN: Anesthetic agents. In Veterinary Ophthalmic Pharmacology and Therapeutics, ed 2, Bonner Springs, 1978, VM Publishing, pp 23–28. Hall LW, Clarke KW: Veterinary Anaesthesia, ed 9, London, 1991, Baillie`re Tindall, pp 105–133. Kern TJ: Anesthetic considerations of the ophthalmic patient. In Short CE, editor: Principles and Practice of Veterinary Anesthesia, Baltimore, 1987, Williams and Wilkins, pp 173–176. Langley MS, Heel RC: Propofol: a review of its pharmacodynamic and pharmacokinetic properties and use

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as an intravenous anaesthetic, Drugs 35:334–372, 1988. Plumb DC: Plumb’s Veterinary Drug Handbook, ed 5, Ames, 2005, Blackwell, pp 327–329 and 1156–1160. Rubin LF, Gelatt KN: Analgesia of the eye. In Soma LR, editor: Textbook of Veterinary Anesthesia, Baltimore, 1971, Williams and Wilkins, pp 489–499. Wilson RP: Complications associated with local and general anesthesia, Int Ophthalmol Clin 32:1–22, 1993.

Canine Bagley LH, Lavach JD: Comparison of postoperative phacoemulsification results in dogs with and without diabetes mellitus: 153 cases (1991–1992), J Am Vet Med Assoc 205:1165–1169, 1994. Batista CM, Laus JL, Nunes N, PattoDos Santos PS, Costa JL: Evaluation of intraocular pressure and partial CO2 pressures in dogs anesthetized with propofol, Vet Ophthalmol 3:17–19, 2000.

Clutton RE, Boyd C, Richards DLS, Schwink K: Significance of the oculocardiac reflex during ophthalmic surgery in the dog, J Small Anim Pract 29:573–579, 1988. Frischmeyer KJ, Miller PE, Bellay Y, Smedes SL, Brunson DB: Parenteral anticholinergics in dogs with normal and elevated intraocular pressure, Vet Surg 22:230–234, 1993. Gelatt KN, Gwin RM, Peiffer RL, Gum GG: Tonography in the normal and glaucomatous Beagle, Am J Vet Res 38:515–520, 1977. Hazra S, De D, Roy B, et al: Use of ketamine, xylazine and diazepam anesthesia with retrobulbar block for phacoemulsification in dogs, Vet Ophthalmol 11:255–260, 2008. Hofmeister EH, Williams CO, Braun C, Moore PA: Influence of lidocaine and diazepam on peri-induction intraocular pressure in dogs anesthetized with propofol– atracurium, Can J Vet Res 70:251–256, 2006. Hofmeister EH, Williams CO, Braun C, Moore PA: Propofol versus thiopental:

Further reading effects of peri-induction intraocular pressures in dogs, Vet Anaesth Analg 35:275–281, 2008. Joffe WS, Gay AJ: The oculorespiratory cardiac reflex in the dog, Invest Ophthalmol 5:550–554, 1966. Magrane WG: Methoxyflurane (metofane) anesthesia in intraocular surgery, Pract Vet 3:75–76, 1967. Seim HB, Creed JE, Smith KW: Restraint techniques for prevention of self–trauma. In Bojrab MJ, editor: Current Techniques in Small Animal Surgery, ed 3, Philadelphia, 1990, Lea and Febiger, pp 42–49. Sullivan TC, Hellyer PW, Lee DD, Davidson MG: Respiratory function and extraocular muscle paralysis following administration of pancuronium bromide in dogs, Vet Ophthalmol 1:125–128, 1998. Vestre WA, Brightman AH, Helper LC, Lowery JC: Decreased tear production associated with general anesthesia in the dog, J Am Vet Med Assoc 174:1006–1007, 1979.

Young SS, Barnett KC, Taylor PM: Anaesthetic regimes for cataract removal in the dog, J Small Anim Pract 32:236–240, 1991.

Feline Hahnenberger EW: Influence of various anesthetic drugs on the intraocular pressure of cats, Von Graefes Archiv fu¨r klinische und experimentelle Ophthalmologie 199:179–186, 1976. Mester U, Stein HJ, Pillat-Moog U: Experiences gained with a combination ketamine anaesthesia for eye surgery on cats, Von Graefes Archiv fu¨r klinische und experimentelle Ophthalmologie 201:289–294, 1977.

Horse Brooks DE: Ophthalmology for the Equine Practitioner, 2009, Teton New Media, Jackson, pp 17–29. Hendrix DVH: Eye examination techniques in horses, Clinical Techniques in Equine Practice 4:2–10, 2005.

Miller-Michau T: Equine ocular examination: basic and advanced diagnostic techniques. In Gilger BC, editor: Equine Ophthalmology, St Louis, 2005, Saunders, pp 1–62. Robertson SA: Standing sedation and pain management for ophthalmic patients, Vet Clin North Am Equine Pract 20:485–497, 2004.

Food and fiber-producing animals Donaldson LL, Holland M, Koch SA: Atracurium as an adjunct to halothane– oxygen anesthesia in a llama undergoing intraocular surgery: a case report, Vet Surg 21:76–79, 1992. Pearce SG, Kerr CL, Boure LP, Thompson K, Dobson H: Comparison of the retrobulbar and Peterson nerve block techniques via magnetic resonance imaging in bovine cadavers, J Am Vet Med Assoc 223:852–855, 2003. Skarda RT: Local and regional anesthesia in ruminants and swine, Vet Clin North Am Food Anim Pract 12:579–626, 1996.

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CHAPTER

4

Surgery of the orbit Kirk N. Gelatt1 and R. David Whitley2 1

Small animals; 2Large animals and special species

Chapter contents Surgical management of orbital diseases

51

Orbitotomy in small animals

76

Ancillary diagnostic procedures

52

Total and partial orbitectomy

81

Surgical anatomy of animal orbits

53

Orbitotomy in large animals and special species

81

Surgical pathophysiology

57

Perioperative medications

59

Surgical management of traumatic proptosis in small animals

82

TYPES OF ORBITAL SURGICAL PROCEDURES

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Surgical augmentation of orbital volume in small animals

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Enucleation procedures in small animals

60

POSTOPERATIVE CARE AND MANAGEMENT

84

63

Postoperative complications and treatment in all species

84

Exenteration in small animals

67

Short- and long-term results in all species

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Enucleation procedures in large animals and special species

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Evisceration with intraocular prosthesis in small animals

Surgical management of orbital diseases Orbital diseases of small animals are common in veterinary practice and are often treated with a combination of medical and surgical modalities. Orbital diseases in animals are traditionally classified into those that cause exophthalmia (which is the largest group) and those associated with enophthalmia. Exophthalmia refers to an abnormal prominence or protrusion of the globe, and is associated with space-occupying diseases, including inflammations, cysts and neoplasms. Exophthalmia can be confused with megaloglobus or buphthalmia when prominence of the eye results from an enlarged globe, as in the glaucomas. Enophthalmia, which is less frequently encountered in veterinary ophthalmology practice, occurs when the globe is recessed into the orbit or is less prominent. Enophthalmia is associated with congenital orbital disorders, pain from inflammation, microphthalmia (a smaller than normal globe), phthisis bulbi (atrophy of the eye secondary to ciliary body destruction and limited to absent aqueous humor production), Horner’s syndrome, dehydration, loss of orbital fat, and fibrosis within the orbit.

Defining the margins of orbital disease Orbital diseases, particularly diffuse septic inflammation and expansive neoplasms, usually infiltrate the orbit within its fascial planes and confound determination of the disease margins, thereby limiting the success rate of surgery or radiotherapy. Before entering the orbit surgically, the disease process and its borders should be identified as best as possible, by the different imaging modalities, as thoroughly as possible. The orbit is highly vascular, and visualization of the different structures during surgery is often limited using only one technique. Vital nerves, blood vessels, and extraocular muscles span the orbital space between the different bony foramina and the globe, tear glands, nictitating membrane, conjunctiva, and eyelids. Although imaging procedures such as computed tomography (CT) and magnetic resonance imaging (MRI) are expensive, they often yield the best results. Fortunately, however, the orbit can be evaluated by a number of physical examination procedures, as follows. When exophthalmia is the presenting primary clinical sign, a number of additional more subtle clinical signs

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Surgery of the orbit

may assist in determining whether the space-occupying disease is inflammatory, cystic, or neoplastic. Primary orbital diseases associated with exophthalmia are usually unilateral, and comparisons of the orbital position and size of both eyes can be informative. If the exophthalmia is bilateral, systemic disease should be suspected. The inability of the animal to retropulse the globe or retract the globe upon eyelid or corneal touch often signals a sizeable space-occupying disease. With orbital inflammatory diseases, retraction of the extraocular muscles and globe may also elicit pain. With orbital cysts or neoplasia, the retropulse reflex is impaired but usually elicits no pain. Imaging techniques to evaluate the orbit initially include plain and special contrast radiologic procedures, and ultrasonography. More sophisticated diagnostic procedures such as CT and MRI offer the best imaging of orbital tissues, and fortunately their availability is increasing.

Strabismus and orbital diseases Strabismus refers to deviation of the globe, and is traditionally divided into dorsal (hypertropia), ventral (hypotropia), lateral (exotropia), and medial (esotropia). Primary strabismus without ocular disease is rare in animals. It has been reported in horses and mules, cattle, and dogs, but appears most frequent in cats, especially the Siamese and Himalayan breeds. Uni- or even bilateral strabismus may occur in dogs, secondary to myositis of selected extraocular muscles, and may be complicated by fibrosis of these muscles. Secondary strabismus is frequently present with orbital diseases, and the direction of the deviation of the globe may suggest the location of the space-occupying lesion. When space-occupying orbital disease is directly behind the globe and confined to the retrobulbar muscle cone, the eye is usually displaced directly forward. The pressure on the globe may be sufficient to indent areas of the posterior segment and be detectable ophthalmoscopically. If the space-occupying mass is located within the medial or ventromedial orbital or zygomatic salivary gland in animals, the resultant strabismus is usually lateral (exotropia) and/or dorsal (hypertropia). If the mass involves the rostral aspect of the medial orbit, the eye may be deviated upward, and the nictitating membrane is usually protracted. If the mass is located within the rostral aspect of the dorsal orbit, the eye is usually deviated downward (hypotropia). In spite of the strabismus, tonic eye reflexes and eye movements are usually normal.

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either resection or recession of affected extraocular muscles. The surgery is carried out at their insertions to the anterior globe, and is relatively easy to perform. Occasionally lateral strabismus develops after traumatic proptosis, and signals either nerve and/or muscle injury to the medial rectus muscle. If exotropia results from damage to the oculomotor nerve, spontaneous recovery often occurs. If the muscle or its insertion to the globe has been transected, recovery is unlikely. Attempts to reattach the severed ends of the medial rectus muscle are not usually successful as the deeper (proximal) aspects of the medial rectus cannot be located. Splitting the dorsal rectus muscle longitudinally and repositioning the medial portion to the medial rectus insertion provides satisfactory results. A fairly recent disorder in dogs, extraocular muscle myositis (also called fibrosing strabismus), usually presents with uni- or bilateral restrictive ventromedial strabismus and enophthalmia. Several breeds of dogs appear affected, but the large breeds as well as the Chinese Shar Pei seem most often affected. Involved muscles include the ventral rectus, ventral oblique, and medial rectus. Medical therapy includes immunosuppressive systemic therapy (prednisone and/or azathioprine) and early cases are the most responsive. Surgical correction usually involves resection of the affected muscle(s) or their insertion(s) rather than recessing the opposite muscle to straighten the globe (because of the inflammation and subsequent fibrosis of the affected muscles).

Ancillary diagnostic procedures If surgery on the orbit is anticipated, additional diagnostic procedures that can assist to define the borders of the orbital disease, and perhaps the type of mass, are recommended. Plain and contrast radiography, combined with B-scan ultrasonography, usually provides the most valuable basic information in most veterinary centers. Special radiographic procedures include venography, arteriography, optic nerve thecography, and the direct injection of air (pneumo-orbitography) or contrast material (positive contrast orbitography) into the orbit. Needle biopsy with B-scan ultrasonography may indicate the histologic characteristics of the orbital mass. CT scans and MRI have markedly improved the diagnosis and definition of orbital diseases in animals, but are currently limited to academic veterinary medical hospitals and large clinical centers.

Strabismus (rectus muscle) surgery

Incomplete orbital walls in domestic animals

Strabismus surgery is infrequently performed because the ocular malalignment usually signals ophthalmic disease. Extraocular muscle surgery for strabismus in the Siamese cat with esotropia has not been successful because of the very small rectus muscles in the cat as well as the underlying neuro-ophthalmic tract malformation. The congenital exotropia occasionally seen in brachycephalic breeds of dogs has not been treated with rectus muscle surgery. Strabismus is infrequent in horses and mules, and some affected horses may also exhibit night blindness (e.g., Appaloosa breed). Strabismus in the horse has been successfully treated by

In contrast to humans, most small and large animal orbital walls are incomplete caudoventrally and laterally. In the primate the contents of the entire orbit are bounded by bone, thereby providing maximum protection for the globe. In many avian species orbits are unusually large and often limit access through only the frontal aspects (like human and non-human primates). The incomplete orbital walls in dogs and cats seem associated with the ability to open the jaw as widely as possible. As a result, the coronoid process of the mandible is medial of the zygomatic arch and in the caudolateral orbit. Hence, in orbital diseases, especially

Surgical anatomy of animal orbits

acute inflammations, manipulation of the mouth will usually elicit pain. Where the bony orbital walls are missing in carnivores, the wall is replaced with a variable thickness fascial layer, the endorbita (or periorbita). In the caudal, dorsal, and lateral orbital walls, the temporalis, masseter, and pterygoid muscles are adjacent to the endorbita. The endorbita constitutes a reasonable barrier to inflammation, trauma, and neoplasia, but still does not provide the protection provided by bony walls. As a result, orbital diseases in small animals may extend from the orbit into the mouth via the caudal floor, perforate anteriorly to the conjunctival surfaces, or extend laterally into the subcutaneous tissues of the lateral orbit and face. While these regional soft-tissue orbital walls represent incomplete and weaker barriers, these same areas provide potential entry routes for surgical invasion of the orbital space.

Enophthalmia and surgery Enophthalmia (recession of the globe within the orbit) is a common clinical sign when the orbital contents are less than normal. The palpebral fissure may be reduced in size. The most frequent condition with enophthalmia is microphthalmia, a congenital and sometimes inherited condition, and phthisis bulbi or atrophy of the eye, an acquired disorder. Enophthalmia can also accompany Horner’s syndrome, the loss of fat associated with debility, dehydration, and pain. An emerging clinical problem in large and giant breeds of dogs is the ‘medial canthal pocket syndrome’, which consists of bilateral enophthalmia, persistent and chronic conjunctivitis, and entropion and/or ectropion secondary to the lack of support and contact between the globe and eyelids. This condition, occurring more frequently in male dogs, is associated with very large heads and deeply recessed eyes. It is difficult to treat medically and/or surgically and resolve. Augmentation of the volume of the orbit with a visual eye has been attempted by adding autogenous fat (usually about 70% is lost before its blood supply is restored), sterile glass beads (about 4–5 mm diameter), medical grade silicone, and newer microporous implants that permit vascular ingrowth into the device.

Surgical anatomy of animal orbits The orbit consists of walls that are either bone or muscle combined with fascia that confine and protect the globe. The anatomy of the orbit differs widely among humans and animals, and these differences modify the clinical manifestations of orbital diseases and their surgical approaches. The orbit in humans and animals is roughly conical in shape, with the apex of the cone directed ventroposteriorly and medially, and the base of the cone accommodating the globe and supporting tissues. Through the apex traverse the different nerves to innervate the extraocular muscles, the sensory nerves to the globe and surrounding structures, and the optic nerve linking the retina to the midbrain and higher visual centers. Adjacent areas, such as the frontal and maxillary sinuses, and the teeth roots within the maxillary bone, are frequent sites of infection and neoplasia that may extend into the orbit and produce clinical disease.

Canine orbit The bones that envelop and confine the orbital tissues in the dog consist of the zygomatic process of the frontal bone dorsally; the frontal bone and palatine bones medially; and the zygomatic arch and vertical ramus of the mandible laterally (Fig. 4.1a). The bony orbital floor is comprised of the sphenoid bone. The orbital rim consists of the zygomatic process of the frontal bone dorsally, the lateral orbital ligament, and parts of the zygomatic, maxillary, and lacrimal bones ventrally. Soft tissues that support the orbital walls include the temporalis muscles posteromedially, the temporalis and pterygoid muscles medially, the masseter muscle laterally, and the medial pterygoid muscle ventrally. The zygomatic or orbital salivary gland is located in the dog in the rostrolateral orbit. In brachycephalic breeds of dogs the orbit is very shallow, while in dolichocephalic breeds the orbit is considerably deeper and difficult to access surgically. The major arteries in the dog orbit are located along the ventral and ventromedial floor, and consist of the pterygopalatine portion of the maxillary artery with its various branches, including the external ophthalmic (orbital) artery, the infraorbital artery, the minor palatine artery, and a trunk that gives rise to the major palatine and sphenopalatine arteries. From the external ophthalmic artery are branches that include the external ethmoidal artery and the anastomotic ramus to the internal carotid artery. Branches from the external ethmoidal artery include, in part, the ventral and dorsal muscular branches to the extraocular muscles, the lacrimal and zygomatic branches. With the union of the external and internal ophthalmic arteries emerge two to four long posterior ciliary arteries to supply the globe. The orbital veins tend to follow the respective arteries, and, in addition, form an extensive and highly variable orbital venous plexus. With the origin of the majority of the extraocular rectus muscles in the apex of the orbit, these muscles span the orbit to insert anterior to the globe’s equator. The four bellies of the retractor oculi muscle envelop the optic nerve, and attach to the globe posterior to the rectus muscle insertions. The ventral oblique muscle has its unique origin in the medial orbital wall. Immediately above the dorsal rectus muscle is the levator palpebrae superioris muscle, with its common origin with the other rectus muscles but its insertion in the tarsal layer of the upper eyelid. In addition to an extensive arterial and venous supply, and space-filling adipose tissues, all the orbital tissues are covered with endorbita or the periorbital fascia that eventually merges with the fascia bulbi (or Tenon’s capsule) that surrounds the globe and attaches at the limbus, the periosteum or endorbita lining the orbital walls, and the tarsal layer within the eyelids as the septum orbitale anteriorly. The subTenon’s space between the fascia bulbi and the sclera is an important surgical plane that permits dissection around the globe with minimal hemorrhage. The third (oculomotor), fourth (trochlear), and sixth (abducens) cranial nerves innervate the retrobulbar muscles, and the second (optic), fifth (trigeminal), and branches of the seventh (facial) cranial nerves permit vision, sensation, and lacrimation (Fig. 4.1b). The orbit also contains

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Surgery of the orbit

A

B

Fig. 4.1 The bones of the canine orbit. The dorsolateral wall and caudal floor of the canine orbit consist of soft tissues. Entry into the canine orbit is restricted to these soft tissues avenues, as well as through the palpebral fissure and orbital opening. (a) The canine orbital anatomy varies considerably based on breed and skull type. The bony orbital rim is incomplete, and laterally is formed by the lateral orbital ligament. The bones that comprise the canine orbit include the frontal bone and its zygomatic process (A), palatine bone (B), zygomatic arch (C), and vertical ramus of the mandible (D). The bony orbital floor consists of the sphenoid bone (not visible). The orbital rim consists of the zygomatic process of the frontal bone (see A), and parts of the zygomatic (see C), maxillary (E), and lacrimal (F) bones. The lateral orbital ligament (missing in this specimen) extends from the zygomatic process of the frontal bone to the zygomatic arch (arrows). Surgical access to the canine orbit is generally through the orbital rim or through the lateral orbital wall, with or without the central zygomatic arch removed. (G) indicates the lacrimal fossa which contains the lacrimal sac. (b) The three important foramina in the apex of the canine orbit are: (A) optic foramen, through which the optic nerve and internal ophthalmic artery pass; (B) orbital fissure, through which the third, fourth and sixth cranial nerves, the ophthalmic division of the trigeminal (fifth) nerve, and the orbital vein pass; (C) rotundum foramen, through which the internal maxillary nerve and artery pass.

autonomic fibers, with the sympathetic fibers extending from the superior cervical ganglion, and parasympathetic fibers entering the orbit to synapse in the ciliary ganglion. Parasympathetic fibers from the ciliary ganglion then continue to innervate the iris sphincter and ciliary body muscles. Canine orbit size varies by breed and skull type. In general, skull length, width, and height range from about 156  27  29 mm in mesaticephalics, 79  28  30 mm in brachycephalics and 214  33  29 mm in dolichocephalics. There is an increase in orbital size from the toy to giant breeds, but the increase is not directly proportional. The canine globe size ranges from 19.7 to 25 mm transverse, 18.7 to 25 mm vertical, and 20.0 to 25 mm anteroposterior.

Feline orbit The orbit of the cat is similar but not identical to the dog. In contrast to the dog, the feline orbit is only slightly larger than the globe, which greatly restricts orbital exploration unless the globe is first removed. The bones that compose the orbital walls include the sphenoid, maxillary, lacrimal, zygomatic, and frontal (Fig. 4.2). The lateral orbital ligament joins the frontal and zygomatic processes. The bony floor of the feline orbit consists of only a small shelf of maxillary bone that holds the last molar teeth. The extraocular muscles are small and ocular mobility is limited. The zygomatic or intraorbital salivary gland is small in the cat and lies close to the maxillary nerve. The cat’s orbital measurements are about 87 mm long, 26 mm wide, and 23 mm high. The feline globe ranges in size from 20 to 22 mm anteroposteriorly, 19 to 20.7 mm vertically and 18 to 21 mm transversely. The larger Siamese breed globes measure 22.5 mm anteroposteriorly and 22.5 mm transversely.

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Horse orbit Both the horse and cow orbits are among the largest that clinically confront the veterinarian. The orbital bones in the horse include the frontal, lacrimal, zygomatic, temporal, sphenoid, palatine and maxillary (Fig. 4.3a). The bones contributing to the equine orbital rim include the lacrimal (ventromedial orbital rim), the frontal and its zygomatic process (dorsal orbital rim), and the zygomatic processes of the temporal and zygomatic bones (incomplete lateral wall and lateral canthus). The zygomatic process of the frontal bone contains the supraorbital foramen, an important landmark for supraorbital nerve blocks to produce upper eyelid regional anesthesia and paralysis. Hence, the entire orbital rim in horses consists of bones and no fascial tissues or ligaments. The lacrimal bone contains both a shallow fossa for the poorly developed lacrimal sac as well as the entry of the nasolacrimal system into the nasal turbinates. The complete medial orbital wall consists of contributions from the frontal and lacrimal bones and the wing of the presphenoid bone. The dorsal wall is formed by the frontal and, to a smaller extent, the lacrimal bones. The incomplete ventral wall is formed by the zygomatic bone and, to a limited extent, the maxillary and palatine bones. The incomplete lateral wall is formed by the zygomatic processes from both the temporal and zygomatic bones, and the periorbita. A significant lateral barrier to the deep orbital structures is the large coronoid process of the mandible. Four important foramina are sited in the apex of the orbit (Fig. 4.3b). They include: 1. the ethmoid foramen – entry for ethmoid blood vessels and nerves 2. the optic foramen – exit of the optic nerve

Surgical anatomy of animal orbits

A

B

Fig. 4.2 The bones of the feline orbit. Entry into the feline orbit is generally limited to the palpebral fissure and orbital opening. View of the feline skull from the side (a) and from the front (b). The bony orbit provides little more than the essential space to accommodate the cat globe. Like the dog, the bony orbital rim is incomplete laterally and this area is formed by the short lateral orbital ligament. The bones that comprise the cat orbit are, from the side (a): frontal (A), lacrimal (B), maxillary (C), and zygomatic (D). The medial orbital wall (E) consists of the frontal bone dorsally and the sphenoid and palatine bones ventrally. The cat orbital floor is incomplete and very thin. As viewed in the apex of the orbit (b), the dorsal optic foremen and ventrolateral orbital fissure (E) permit passage of the essential ophthalmic nerves and vessels. The globe and orbit accommodate fairly short optic nerves, and very small and limited mobility extraocular muscles.

A

B

Fig. 4.3 The bones of the equine orbit. Entry into the equine orbit is generally limited to the palpebral fissure and orbital opening. Although the dorsolateral orbital wall and caudal floor of the orbit consist of soft tissues, these avenues provide very limited access to the caudal orbit as the extraocular muscle cone, vital blood vessels, and cranial nerves are so deep! (a) The bones that comprise the equine orbit, as viewed laterally, consist of the frontal bone with large supraorbital process (A), zygomatic arch (B), the coronoid process of the mandible (C, not part of the orbit but within the orbit), lacrimal bone (D), and zygomatic bone (E). The medial bony orbital wall is formed by the frontal, lacrimal, and wing of the presphenoid bones. The dorsal orbital wall is formed by the frontal and small part of the lacrimal bones. The ventral floor is formed by the zygomatic bone, zygomatic process of the temporal bone and small part of the maxillary bone. The incomplete lateral wall is formed by the zygomatic bones. In contrast to the dog and cat orbital rims, the horse orbital rim is all bone with limited access to the dorsal orbit structures. (b) At the apex of the equine orbit are four important foramina (arrow): most dorsal and medial is the ethmoidal foramen (passage of the ethmoidal artery, vein, and nerve); more ventrad and further caudad is the optic foramen (passage for the optic nerve and internal ophthalmic artery); just ventral is the orbital fissure (carrying the third, sixth and often the fourth or trochlear and ophthalmic division of the trigeminal nerves); and lastly is the furthest ventral foramen, the round foramen (passage of the maxillary nerve). The apex of the orbit is a considerable distance from the globe (longer than the cow), and generally approached immediately caudal of the supraorbital arch.

3. the orbital fissure – transmits the ophthalmic branch of the trigeminal nerve, the oculomotor (third) nerve, the abducens (sixth) nerve, and often the trochlear (fourth) nerve 4. the round foramen – maxillary branch of the trigeminal nerve.

In the placement of successful retrobulbar nerve blocks in the horse, at least 8–10 cm of distance must be traversed by the hypodermic needle to inject local regional anesthetic in the vicinity of these four foramina. The orbital dimensions of the adult horse are estimated to be 62 mm wide, 59 mm high, 98 mm deep, and

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173 mm between the eyes. The adult horse globe measures 43.7 mm on the meridional anterior–posterior axis, 47.6 mm on the equatorial axis vertical, and 48.5 mm on the horizontal axis.

Cow orbit The cow orbit has many similarities to the horse, but also significant differences. For instance, the frontal bone is very large and well developed to accommodate the cow’s horns. The bones which contribute to the bovine orbit include the frontal, lacrimal, zygomatic, palatine, maxillary, and sphenoid. The bovine orbital rim, composed of three bony structures around 360 , consists of: 1) the frontal bone (dorsal rim); 2) the lacrimal bone (medial canthus); and 3) the zygomatic bone and frontal process of the zygomatic bone (entire ventral rim and lateral canthus). The coronoid process of the mandible is well developed and positioned just caudal to the lateral rim to permit hypodermic needle insertion into the deep orbital tissues from behind the lateral orbital rim (Fig. 4.4a). The bony orbital walls consist of: 1) the lacrimal and sphenoid bones medially; 2) the palatine and sphenoid bones ventrally; 3) the frontal bone dorsally, and 4) the temporal and zygomatic bones laterally. Important orbital foramina include: 1) the ethmoidal foramen (ethmoidal blood vessels and nerves); 2) the optic foramen (passage of the optic nerve); and 3) the orbitorotundum (a combination of the orbital fissure and the foramen rotundum) for passage of the oculomotor (third), the trochlear (fourth), the trigeminal (fifth) and the abducens (sixth) nerves, and retinal and maxillary blood vessels (Fig. 4.4b). The orbital dimensions of the adult cow are estimated to be 65 mm wide, 64 mm high, 120 mm deep, and 151 mm between the eyes. The adult cow globe measures 35.3 mm on the meridional anterior–posterior axis, 40.8 mm on

A

the equatorial axis vertical, and 41.9 mm on the horizontal axis. Hence, for a successful retrobulbar injection in cattle, the hypodermic needle, if positioned near the optic and orbitorotundum foramina, must traverse a distance of about 12 cm.

Rabbit orbit The rabbit has become an increasing popular household pet, as it can be house broken and trained to use a litter box. The rabbit has a large orbit as well as a large globe which occupies most of the orbital space, and a large venous sinus within the orbit. Hence, orbital surgery in this species must be limited to the space between the sclera and Tenon’s capsule, and avoid entering the retrobulbar tissues directly. The bones of the rabbit orbit include the maxillary, orbitosphenoid, alisphenoid, lacrimal, palatine, frontal, pterygoid, and zygomatic. The orbital rim consists of the following bones: frontal bone dorsally, lacrimal bone anteriorly, zygomatic processes of the maxilla, and zygomatic bones (ventral orbital rim). The globe’s lateral displacement allows the temporal bone to also contribute to the lateral orbital rim. The orbit is roughly circular, about 25 mm diameter, with the skull being about 108 mm long and 50 mm wide. The rabbit’s globe measures 16–19 mm anteroposteriorly, 17 mm vertically, and 18–20 mm horizontally. A large Harderian gland (19 mm long, 12–15 mm wide, and 4–6 mm thick at its largest point) occupies the lower anterior part of the orbit. It is medial to the lacrimal gland and almost completely surrounded by a large venous sinus. A very small intraorbital gland is beneath the zygomatic arch.

Avian orbit Avian species that are presented to veterinarians for eye disease are generally in the raptor group (owls, falcons, and hawks) and the psittacines (parrots, cockatiels, and

B

Fig. 4.4 The bones of the bovine orbit. Entry into the bovine orbit is generally through the palpebral fissure and orbital opening. (a) The bones that comprise the cow orbit, as viewed laterally, are the frontal bone with zygomatic process (A), lacrimal bone (B); zygomatic bone with frontal process (C); zygomatic process of the temporal bone (D); and coronoid process of the mandible (E). (b) Viewed through the orbital rim and into the orbital base or apex, are three foramina: the ethmoidal foramen (A); optic foramen (B), lateral to which is the pterygoid crest; and lastly the foramen orbitorotundum (C). Like the horse, the cow orbital rim consists totally of bony structures, but the orbit is shallower than the horse. The pterygoid crest presents a sizeable barrier to orbital nerve blocks (shielding all of the important foramina), and generally local anesthetic is injected deep to it (the pterygoid fossa) or just anterior to successfully block all of the nerves supplying the orbit and globe.

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Surgical pathophysiology

parakeets). Trauma in the raptor group is probably the most frequent single cause of eye disease in this group, and the most treatable. Orbital anatomy varies markedly in the avian species, based on the shape of the skull and beak (Fig. 4.5). The avian orbit and globe are unusually large relative to the bird’s head and body. The large globes result in restricted access to the extraocular muscles as well as limited orbital space during surgery. In fact, sometimes it is best to rupture the globe at the beginning of the enucleation procedure to facilitate surgery and globe removal. Since there is considerable variation in skull and orbital osteology, only some generalizations are possible. In most birds the orbit is almost completely enclosed by bones, the floor being the main exception (contains muscles related to jaw movements). Bones contributing, in part, to the avian orbit include: 1) prefrontal or lacrimal bone; 2) frontal bone; 3) ethmoid or ectethmoidale bone (part of the rostral wall of the orbit, separating it from the nasal cavity); 4) laterosphenoidale bone (ventral caudal wall of orbit); and 5) zygomatic bone. Often pneumatization of the skull bones is present; the reduction in weight of these bones is probably an adaptation for flight. Both globes are separated by a thin bony partition, the interorbital septum (ethmoid bone), which can be fractured easily during enucleation if one is not careful. Another interesting adaptation in birds are two muscles, the M. quadratus membranae nictitantis (originates from beneath the origin of the dorsal oblique muscle) and M. pyramidalis membranae nictitantis (originates near the ventral rectus muscle), which combine and rotate round the optic nerve en route to provide motion to the highly mobile nictitating membrane.

A

Surgical pathophysiology The orbit can be characterized as a roughly conical cavity with bony and fibrous periorbital walls that are relatively resistant to expansion. Suspended within the orbit by a continuous covering of endorbita around the blood vessels, nerves, extraocular muscles, and adipose tissues, the globe is provided mobility. The bulbar and fornix conjunctivae are also thin and flexible, and accommodate ocular movements without restriction, while still creating a significant barrier to the environment and potential infections from entering the orbit and eye. As a result, inflammations, cysts, and masses that increase the volume of the orbital tissues will create pressure on these walls and, as the pathway of least resistance, displace the globe forward into the palpebral fissure. Hence, limited increases in orbital tissue volume can lead to exophthalmia; with large amounts of neoplasia or hemorrhage the globe can be proptosed or displaced beyond the palpebral fissure. This infrastructure of fascial tissues, which permit eye mobility and provide the conduit for the blood vessels, nerves, and muscular attachments for the eye to the rest of the head, can also be damaged. Chronic inflammation, surgery of the orbit, and trauma with hemorrhage can cause fibrosis within the orbit sufficient to restrict globe movement and cause enophthalmia. Loss of the orbital adipose tissues, which fill the orbital spaces and act as flexible ‘shock’ absorbers, can develop after significant orbital hemorrhage and elevated intraorbital pressure, and result in enophthalmia. Typically the orbit may be divided into compartments: 1) intraconal (within the extraocular muscle cone); 2) extraconal (within the orbit but outside of the extraocular muscle

B

Fig. 4.5 The bones of the bird orbit. The avian skull varies markedly in size and shape, and is directly influenced by the bird’s beak. Also, the orbits in birds are generally quite large as compared to the associated skull. (a) In general, the avian bony orbit consists of the following bones: (A) frontal bone; (B) lacrimal bone; (C) the interorbital septum (separating both globes), at the caudal border of which is the optic foramen; and (D) nasal bone (forms the basis for the beak). In this Rhea the orbital rim is much smaller than the bony sclerotic ring (E, representing the globe). In general, the avian orbital rim consists of the following bones: sphenoid, lacrimal (or prefrontals) which form the dorsal orbital rim, nasal and frontal. There may also be an ectethmoid bone. (b) In this Macaw parrot skull, the orbit is very large compared to the bird’s skull, and its shape is influenced by its massive beak. The globes are larger than the orbital rim, requiring special surgical procedures for surgical removal (enucleation) of the globe.

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cone); and 3) extraendorbital (beneath the periosteum of the orbital bones). Intraconal diseases typically cause exophthalmos, while the more frequent extraconal diseases produce strabismus. After orbital surgery, the intraorbital pressure secondary to postoperative hemorrhage and edema may produce some exophthalmos, prolapse of the nictitating membrane, and an impaired blink reflex. If eyelid function is impaired, corneal ulceration can develop rapidly. Hence, after most orbitotomies a partial-to-complete temporary tarsorrhaphy is indicated. Drainage tubes can also be used, separate from the primary incision, to reduce intraorbital pressure and promote drainage. These Penrose drains should be removed 24–48 h postoperatively.

Effect of globe development on orbit growth Development of puppy, kitten and foal orbits is partially determined by concurrent growth and expansion in the size of the eye. In animals that lose an eye to trauma and/or inflammation in early life and while still growing, orbital development will markedly slow and result in noticeable orbital asymmetry at adulthood. The earlier in life that the globe is destroyed, the more pronounced the orbital defect. Orbital asymmetry also occurs in puppies, kittens and foals with unilateral microphthalmia: the more severe the microphthalmia, the more extensive the orbital maldevelopment. Hence in young animals, enucleation of the globe and use of an intraorbital implant after surgery usually help to reduce the orbital deformity to a minimum.

Traumatic proptosis/avulsion/luxation of the globe In proptosis or luxation of the globe, the entire globe is displaced forward. In mild cases, secondary pressure from retrobulbar hemorrhage and edema will force the globe forward sufficiently to induce exophthalmia, exposure keratitis, and an impaired blink reflex. Proptosis occurs most frequently in dogs and certain breeds, especially the brachycephalic breeds, and in cats is usually catastrophic. In the horse, traumatic proptosis is usually incomplete and is typically exhibited by intraorbital hemorrhage, exposure keratitis, exophthalmia, and impaired blink reflex. In other species, proptosis appears rare. When trauma is extensive, the globe may be thrust forward with such force and speed that the equator of the globe extends beyond the palpebral fissure. The compensatory eyelid contractions that should retain the globe within the orbit are delayed, and with the globe already forward of the eyelid margins, the orbicularis oculi muscle spasms prevent retraction of the globe into the orbit. At the same time, forward stretching of the orbital tissues results in intraorbital hemorrhage and edema which can displace the globe even further forward. The stretching, direct pressure, and perhaps thrombosis and ischemia can result in optic nerve inflammation and subsequent atrophy. Elevated intraorbital pressure, and nerve and vascular damage to the lacrimal gland, may cause sufficient destruction to result in keratoconjunctivitis malacia. The extraocular muscles are stretched considerably in traumatic proptosis, and the shortest medial rectus muscle may be transected near its insertion. The impaired

58

blink reflex results in acute corneal exposure and rapidly progressing malacia. Unchecked, the corneal integrity can be compromised within hours. Medical and surgical treatment strategies that directly address the primary and secondary events that can occur in traumatic proptosis are the most successful.

Orbital fractures As the orbital shell is composed primarily of bony tissues, the globe is fairly well protected against trauma. However, considerable trauma can cause orbital fractures of the temporal, zygomatic and frontal bones in most domestic species. With the concurrent hemorrhage and swelling, globe displacement, strabismus, impaired mobility, hemorrhage, pain, and orbital asymmetry result. If the adjacent sinuses are involved, orbital and/or subcutaneous emphysema with crepitus occur. In general, orbital fractures with minimal displacement of the fractured bone heal without surgery; however, if displacement is considerable and unstable, reapposition and internal fixation of the fractured fragments is recommended. A vigorous blink reflex must be maintained in spite of the orbital swelling, and the cornea protected by topical tear substitutes. Temporary complete tarsorrhaphy may be indicted to protect the outer eye and prevent secondary corneal ulceration.

Orbital inflammation: acute and chronic The animal orbit is susceptible to bacterial infections (Fig. 4.6). Orbital cellulitis may present as acute or chronic, and is usually associated with bacterial or fungal infections (often entry cannot be ascertained), as well as foreign bodies. Orbital cellulitis occurs most frequently in dogs (especially the hunting breeds), and is rare in cats. In horses, cattle, and certain species of birds orbital cellulitis may be secondary to adjacent sinus infections or as a sequel of dehorning in cattle. Fungal infections are infrequent in the dog, and are usually associated with foreign bodies. Infection may enter the orbit through several routes. Infectious agents can enter from the mouth, conjunctivae, the adjacent sinuses and nasal cavity, the subcutaneous and skin surfaces of the incomplete lateral and dorsolateral orbital walls, and

Fig. 4.6 English Springer Spaniel with acute orbital cellulitis. Note the swelling of the eyelids and dorsal orbital subcutaneous tissues.

Perioperative medications

hematogenously. In a recent report on orbital abscesses in dogs and cats, the most common bacterial genera isolated from dogs were Staphylococcus, Escherichia, Bacteroides, Clostridium, and Pasteurella. The most frequent bacteria isolated from orbital abscesses in cats were Pasteurella and Bacteroides. The highly vascular orbit and the endorbita that covers the orbital tissues usually respond quickly to antibiotic therapy. This orbital compartmentalization can also impede the spread of the infectious nidus, but also foster the development of focal septic areas that impede antibiotic penetration. As a result, surgical excision of chronic orbital abscesses and focal granulomas may be necessary for complete resolution of the condition. For orbital abscesses in dogs and cats, based on in-vitro susceptibility testing of aerobic bacterial isolates, cephalosporins, extended-spectrum penicillins, potentiated penicillins, and carbapenems are recommended for the initial antimicrobial therapy of orbital abscesses in dogs and cats. Antimicrobial culture is recommended for any severe orbital abscess and in-vitro antimicrobial susceptibility determined to assist in antibiotic selection.

Orbital neoplasms Orbital neoplasms are not infrequent in dogs, but are less common in cats. In both horses and cattle, intraorbital lymphomas, lymphosarcomas, and squamous cell carcinomas are the most frequent types. In dogs, orbital neoplasms consist of a large number of different tumor types, while in cats the most frequent orbital neoplasm is squamous cell carcinoma. Primary orbital neoplasms can arise from any tissue (epithelial, vascular, neural, and connective tissues) within the orbit. Secondary orbital neoplasms also occur and invade locally from the nasal, sinus, and cranial cavities, as well as metastasize from distant sites. The clinical signs of orbital neoplasia are usually associated with a slowly enlarging and painless mass within the orbit (Fig. 4.7). Depending on its position, a neoplasm within the orbit can produce strabismus; the direction of the ocular deviation may assist to localize the mass. The majority of information on orbital neoplasia is on dogs. The mean age of affected dogs with orbital neoplasms is 8–9 years old. Females may be at higher risk. There is no

breed predisposition. Younger dogs may demonstrate more rapidly growing orbital masses. Most neoplasms external to the extraocular cone affect the medial orbital space and wall. This area has the most difficult and limited surgical exposure. In dogs, about 60% of orbital neoplasms are primary. As a result, when orbital neoplasia is suspected, a complete and comprehensive general physical examination is required. The remaining 40% of orbital neoplasms usually invade the orbit from the adjacent nasal and oral cavities, and the sinuses. Unfortunately, 90% of canine orbital neoplasms are malignant. The prognosis for orbital neoplasms is poor, because conservative surgery in an attempt to maintain the globe and vision results in unacceptably high rates of tumor recurrence. Patients with orbital osteolysis usually have a poor prognosis. Most clients do not accept the aggressive attempts of orbitectomy with the resultant loss of the globe and vision, and postoperative facial deformities. A recent study reported that surgical intervention and chemotherapy can prolong life; about 40% of the dogs were alive 6 months after diagnosis, and about 19% were still alive 1 year later. Unfortunately, the other 60% of patients, with advanced orbital neoplasia and most with no therapy, were euthanized within 6 months of diagnosis. The treatment of choice is usually exenteration, which involves excision of the entire orbital contents including the globe. Orbital neoplasms affecting the rostral and lateral orbit may be successfully excised while preserving the eye. Unfortunately, masses involving the ventromedial and posterior orbit, which are the most frequent, generally require removal of the eye during attempts at excising the neoplasm. A major difficulty during surgery is the differentiation of normal and cancerous tissues, often resulting in an incomplete excision of the neoplasm. When considering extensive therapy for advanced orbital neoplasia in small animals and horses, careful education of the client is very important as the postoperative results can markedly affect the facial appearance. Orbital neoplasms in cats are usually malignant. The orbital neoplasms reported most frequently include squamous cell carcinomas, followed by lymphosarcoma– leukemia complex, undifferentiated sarcomas, osteogenic sarcomas, and rhabdomyosarcoma. Orbital neoplasia in cats necessitates a guarded to very poor prognosis. Orbital neoplasia is infrequent in horses and cattle, and careful systemic patient evaluation is essential. Conjunctival squamous cell carcinomas may invade the orbit, especially in the medial canthus. Retrobulbar lymphosarcoma occurs in both species, and not infrequently affects both orbits. The appearance after enucleation or exenteration in horses is a greatly shrunken orbit, and an intraorbital prosthesis may prevent most of the shrinkage.

Perioperative medications

Fig. 4.7 Left orbital neoplasm (meningioma) affecting the medial orbital floor in a 15-year-old Beagle. Note the exophthalmos and dorsolateral deviation of the globe.

Orbital surgery may be performed with the patient under various medications for the pre-existing ophthalmic condition. Topical and systemic antibiotics are often indicated prior to orbital surgical procedures when sepsis is present. When entry into the internal orbit or globe through the conjunctival surfaces is planned, complete asepsis is not

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possible. If an intraocular or an intraorbital prosthesis is implanted, topical and systemic antibiotics are recommended perioperatively. If infection occurs postoperatively around the prosthesis, successful resolution of the condition often necessitates removal of the device. For lateral and dorsal orbitotomy procedures, standard skin preparation is recommended. The planned surgical site is clipped, and cleaned with surgical antimicrobial soap. The area is wiped with iodine (0.5% dilution) and alcohol, and carefully draped, leaving the surgical area exposed. For enucleation and other surgical procedures performed through the palpebral fissure, the eyelids, corneal and conjunctival surfaces are prepared for surgery as outlined in Chapter 2.

TYPES OF ORBITAL SURGICAL PROCEDURES Orbital surgical procedures are divided into several major types including: enucleation, evisceration, exenteration, orbitotomy, and orbitectomy. In the enucleation procedure the globe is excised in total. Most, if not all, of the bulbar and palpebral conjunctivae, the eyelid margins, and the nictitating membrane are also removed. The lacrimal gland may or may not be excised depending on the enucleation procedure. An intraorbital prosthesis may be used to fill the space occupied by the eye. In birds, the enucleation procedure is unique because of the large globes and small orbital rims. In the avian enucleation technique, either additional exposure is created or the globe is collapsed before removal. In the evisceration procedure, the intraocular tissues, including the anterior and posterior uvea, lens, vitreous, and retina, are removed. After implantation of an intraocular prosthesis, the scleral or limbal incision is apposed, leaving the corneal and scleral tunics. Eye movement with the intraocular implant is retained. In the exenteration procedure the contents of the entire orbit including the globe are excised. This procedure is generally reserved for orbital neoplasia in all animal species. In orbitotomy procedures, selected areas of the orbit are exposed, usually for tissue biopsy and excision. Surgical approaches to the orbit are limited to the oral, anterior, lateral, and dorsal routes. The anterior orbitotomy procedure has two surgical approaches: the transpalpebral (through the eyelids) and the transconjunctival (through the bulbar conjunctiva) to gain entry into the anterior orbit. The lateral and dorsal approaches provide access to the posterior orbit through the corresponding soft tissue orbital walls. Because of limited exposure with most orbitotomy procedures with the globe in situ, as accurate a localization of the surgical site as possible is helpful before surgical intervention. The selection of a specific orbitotomy procedure depends on the species. In dogs, a number of different surgical entries, with or without zygomatic arch removal, are available because of the large lateral and dorsolateral fibrous orbital wall. In cats, orbitotomies are limited to the frontal approach, due to very limited space, large globe size relative to orbit, and short optic nerves which limit globe manipulation. In fact, optic nerve chiasm and optic nerve damage to the fellow eye (opposite eye) sufficient to produce blindness can follow excessive surgical handling and tension of the feline’s optic nerve.

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In large animals, the deep orbits are generally approached frontally, and removal of the globe usually precedes deep orbital surgery. In birds, the intraorbital space is very limited, and enucleation and other orbital surgeries are difficult. In some species, the globe must be reduced surgically during the enucleation procedure. In an orbitectomy procedure, the entire contents of the orbit, including the globe, are excised. In addition, some to most of the orbital bones are removed. This radical procedure is reserved for orbital neoplasms localized to the orbit and without distant metastases. With the loss of these tissues, variable facial disfigurement occurs. Preliminary results with orbital neoplasms in dogs suggest that more extensive surgical methods yield improved survival results compared to the more conservative lateral orbitotomy or exenteration procedures. Silicone or methyl methacrylate implants can be used to fill some of the postoperative space and decrease the anticipated disfigurement.

Enucleation procedures in small animals In enucleation, the globe and its contents are excised. In animals, the indications for enucleation include: 1) ocular congenital defects, such as microphthalmia, that result in chronic problems such as conjunctivitis and keratitis; 2) intraocular infections that have destroyed the globe, and are potential sources of systemic infection; 3) intraocular tumors not amenable to local excision or laser therapy and still confined to the globe (Fig. 4.8); 4) proptosis of the globe with several of the extraocular muscles and/or the optic nerve severed; 5) intraocular inflammation that has destroyed the intraocular tissues and resulted in blindness; and 6) extensive trauma to the globe with the loss of intraocular tissues and without the possibility of successful repair. Enlarged and blind glaucomatous globes may also be treated by enucleation; however, the evisceration procedure followed by insertion of an intraocular prosthesis has largely replaced the enucleation procedure because of superior cosmetic results. Advanced glaucoma secondary to intraocular

Fig. 4.8 Primary mast cell sarcoma involving multiple areas of the limbus with secondary glaucoma in an American Cocker Spaniel. The recommended treatment is enucleation.

Enucleation procedures in small animals

neoplasms and non-specific panophthalmitis is best managed by enucleation. In the enucleation procedure in small animals, the eye, eyelid margins, nictitating membrane, and lacrimal gland are excised. Surgical approaches for enucleation include the subconjunctival (through the bulbar conjunctiva), transpalpebral (through the eyelids), and lateral (a modified palpebral procedure starting at the lateral canthus and removing the inner (deeper) one-half of the upper and lower eyelids). During enucleation of the eye in cats, minimal traction on the globe during the procedure is recommended. Excessive traction on the feline globe undergoing enucleation may damage the optic chiasm and the opposite optic nerve. All orbital tissues (including the globes) that are excised should be examined histologically. Microscopic examination of these tissues can confirm the clinical diagnosis, as well as provide additional information that could affect the postoperative clinical management and long-term prognosis for the animal.

Subconjunctival enucleation The subconjunctival enucleation technique is the simplest and most rapid of these procedures, and the most frequently performed in small animals. Using this method, the globe is excised from its surrounding Tenon’s capsule with the majority of the surgical dissection limited to the sub-Tenon’s space. As a result, this method usually has less hemorrhage intraoperatively and less serum accumulation postoperatively. This technique does not usually remove the conjunctivae and lacrimal gland; however, the entire nictitating membrane is excised. Exposure of the deeper orbital tissues may be limited with this procedure because of the edematous bulbar conjunctiva, but can be enhanced by a lateral canthotomy. In the subconjunctival procedure for enucleation, entry into the orbit is through the bulbar conjunctiva. After completion of draping around the palpebral fissure, a 5–10 mm lateral canthotomy may be performed to increase exposure (Fig. 4.9a). With blunt-tipped tenotomy, strabismus, or Metzenbaum scissors, the full-thickness lateral canthus is cut. Hemostasis is usually achieved by direct pressure with a surgical sponge, if necessary supplemented by point electrocautery. The bulbar conjunctiva and Tenon’s capsule are incised at the 12 o’clock position by curved Steven’s tenotomy, strabismus, or Metzenbaum scissors with blunt tips for about 3–5 mm posterior to the limbus, and the incision extended for 360 (Fig. 4.9b). Using the scissors’ blunt tips, the dissection plane between the sclera and Tenon’s capsule is extended deeper into the orbit until each extraocular muscle insertion is identified (Fig. 4.9c). After isolation with a muscle hook, the tendinous insertions of all of the extraocular muscles are incised. Transection of the extraocular muscle insertions, rather than through the muscle per se, minimizes hemorrhage. As each of the four major rectus muscle insertions is incised, the globe becomes more mobile. After incision of the retractor muscle and oblique muscle insertions, the globe will displace slightly forward. To sever the optic nerve and the adjacent posterior ciliary arteries, a small curved hemostat or enucleation forceps are carefully positioned posterior to the globe (Fig. 4.9d). With curved Metzenbaum scissors or the specially curved enucleation scissors, the optic nerve and surrounding blood

vessels are transected just anterior to the hemostat. Placement of the scissors is critical to avoid any contact with the posterior sclera and to prevent inadvertent incision of the posterior segment of the eye. The globe is carefully removed from the orbit to permit placement of a ligature deep to the hemostat still clamped to the optic nerve and accompanying blood vessels. The orbit is now carefully examined for any bleeders, and ligatures or point electrocautery applied if needed. If an intraorbital implant is not used, parts of the remaining extraocular muscles and periorbital fascia are apposed with 2-0 to 4-0 simple interrupted absorbable sutures to reduce the dead space within the orbit. The remaining bulbar conjunctiva and anterior Tenon’s capsule are apposed with 2-0 to 4-0 simple interrupted absorbable sutures. With closure of the bulbar conjunctiva, 4–6 mm of the eyelid margins (including the medial and lateral canthi, and nictitating membrane) are excised circumferentially with tenotomy or strabismus scissors. The nictitating membrane is protracted, and two hemostats are overlapped and clamped at its base (Fig. 4.9e). The remaining nictitating membrane, complete with gland, is excised by tenotomy or strabismus scissors. The remaining eyelids (including the septum orbitale) are closed and apposed with 3-0 to 5-0 simple interrupted non-absorbable sutures (Fig. 4.9f,g). If an orbital prosthesis is planned, an 18–22 mm sterile silicone sphere (Jardon Eye Prosthetics Inc., Southfield, MI) or methyl methacrylate sphere (Storz Instrument Company, St Louis, MO) is usually selected (Fig. 4.10). The surface of the silicone sphere is scarified or roughened with several incisions via scalpel blade to roughen its smooth surface and facilitate orbital retention. The sphere is inserted, and the extraocular muscles and endorbita are apposed about the sphere. An alternative method is the placement of mesh implants on the anterior surface of the orbital rim to prevent postoperative eyelid and orbital shrinkage.

Transpalpebral (‘en bloc’) enucleation The transpalpebral enucleation technique differs from the subconjunctival procedure in that the surgical entry starts at the level of the eyelids, and the deeper aspects of the eyelids and the entire palpebral, fornix, and bulbar conjunctivae, and nictitating membrane are excised (‘en bloc’ method). This technique is performed more frequently in the large animal species. Although more tissues are excised in this procedure, the conjunctival and corneal surfaces are avoided, thereby reducing the chance of orbital contamination and postoperative infection. This method is preferred when infections of the globe and conjunctival surfaces are present. Because the entire conjunctiva is excised, exposure and visualization of the deeper orbital tissues are facilitated. After draping, the eyelids are apposed with simple continuous 3-0 to 4-0 sutures, thereby closing the palpebral fissure (Fig. 4.11a). The eyelid skin is incised circumferentially by scalpel blade about 6–8 mm from the eyelid margins to avoid the bases of the meibomian or tarsal glands (Fig. 4.11b). The skin incision is carefully deepened until the submucosa of the palpebral conjunctiva is reached. Then, with blunt dissection with Steven’s tenotomy, strabismus or Metzenbaum scissors, the incision is continued under the conjunctival fornices, and onto the globe and

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A

D

B

C

E

F

Fig. 4.9 Enucleation – subconjunctival approach: In this procedure the globe is removed from Tenon’s capsule through a bulbar conjunctival incision at the limbus. After removal of the nictitating membrane, the eyelid margins are removed and permanently apposed. (a) The palpebral fissure is temporarily enlarged by a lateral canthotomy. The lateral canthus is incised by small tenotomy scissors for 5–10 mm. (b) The bulbar conjunctiva and Tenon’s capsule are incised 360 by curved Steven’s tenotomy or strabismus scissors a few millimeters behind the limbus. About 2–4 mm of bulbar conjunctiva are left attached at the limbus, to permit manipulation of the globe with forceps during the enucleation procedure. (c) By blunt–sharp dissection with curved tenotomy scissors, the extraocular muscle insertions to the globe are excised. The globe is rotated in different directions to provide the optimal exposure during the dissection process. (d) The optic nerve is clamped by curved hemostat and transected by curved enucleation or Metzenbaum scissors. Special care is required to prevent touching the posterior globe with the tips of the scissors during optic nerve incision. Once the optic nerve has been cut, the globe can be rotated forward for incision of any remaining fascial attachments. (e) The nictitating membrane is protracted by thumb forceps and its base clamped with two curved hemostats. The structure is excised by Mayo scissors. The lacrimal gland may be removed at this time from beneath the lateral orbital ligament. (f) The two layers of closure include apposition of the rostral portion of Tenon’s capsule by simple interrupted absorbable sutures. The skin–orbicularis muscle layer is apposed with simple interrupted non-absorbable sutures. (g) Two weeks following enucleation in a young Labrador Retriever and suture removal.

under the bulbar conjunctiva (Fig. 4.11c). The procedure continues using the same steps as the subconjunctival method. Dissection within the sub-Tenon’s space between the sclera and Tenon’s capsule will usually minimize hemorrhage. All of the extraocular muscles are severed at their insertions (Fig. 4.11d). Isolation, clamping by curved hemostat, incision of the optic nerve, and removal of the globe follow (Fig. 4.11e). The VicrylW ligature is carefully positioned deep to the hemostat on the optic nerve stump. Closure of the anterior periorbital fascial tissues with simple interrupted 3-0 to 5-0 absorbable sutures, with or without an orbital prosthesis, helps to reduce the dead space within the orbit. The orbital septum within the eyelids is apposed

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with 3-0 to 4-0 simple interrupted or horizontal mattress absorbable sutures (Fig. 4.11f). The eyelid–subcutaneous layer is apposed using the same type of suture and suture pattern. The eyelid skin is apposed with several 3-0 to 4-0 simple interrupted non-absorbable sutures (Fig. 4.11g).

Lateral enucleation In the lateral approach for enucleation, the transpalpebral technique has been modified by the inclusion of a lateral canthotomy to increase further the access to, and visualization of, the deeper orbit. This technique is useful in the dolichocephalic canine breeds and for deep orbits. The eyelids

Evisceration with intraocular prosthesis in small animals

Fig. 4.10 Placement of a 14–22 mm silicone or methacrylate sphere after enucleation in the dog and cat. Two-layer closure is recommended with apposition of the dorsal and ventral periorbita and Tenon’s capsule with simple interrupted absorbable sutures, and the eyelid skin and orbicularis oculi muscle layer with simple interrupted non-absorbable sutures. In both cats and horses these orbital implants are more apt to extrude than in dogs. (Modified with permission from Nasisse MP, van Ee RT, Munger RJ, Davidson MG 1988 Use of methyl methacrylate orbital prostheses in dogs and cats: 78 cases (1980–1986). Journal of the American Veterinary Medical Association 192:539–542.)

are temporarily closed during the surgery by sutures and/or instruments to prevent contamination of the corneal and conjunctival surfaces with the orbital tissues. If the eyelids are closed by instrumentation, the time to suture the eyelids is omitted, while still preventing contamination of the orbit with the outer ocular surfaces. After draping, an 8–15 mm lateral canthotomy is performed with curved Steven’s tenotomy, strabismus, or Metzenbaum scissors (Fig. 4.12a). Starting at the lateral canthus and using Metzenbaum scissors, the upper eyelids and then the lower eyelids are divided into an outer layer consisting of the skin and orbicularis oculi, and an inner layer composed of the tarsal plate including the septum orbitale, and the palpebral conjunctiva (Fig. 4.12b). The blunt tipped curved Metzenbaum scissors, with a combination of cutting and blunt dissection, facilitates this process with minimal hemorrhage. Dissection is continued to include the medial canthus, thereby incorporating the entire palpebral fissure. A curved hemostat may be inserted into this cleavage plane to gently clamp the skin surface. The eyelid skin about 5–7 mm from the eyelid margins is incised 360 with the Metzenbaum scissors (Fig. 4.12c), and the eyelid margins apposed with two or three Allis forceps to close the palpebral fissure and cover the corneal and conjunctival surfaces. The globe is rotated medially and the lateral canthal ligament attachment to the orbital rim incised to provide additional mobility to the globe (Fig. 4.12d). Surgical dissection with tenotomy or strabismus scissors is continued under the conjunctival fornices and to the subTenon’s space just caudal of the limbus. Removal of the globe from Tenon’s capsule continues using a method similar to that described in the subconjunctival enucleation technique, except that the medial globe attachments are excised last. The insertions of all of the dorsal, lateral, and ventral extraocular muscles are transected by scissors immediately next to the globe to minimize hemorrhage. As the different extraocular muscles are transected, the globe can be progressively rotated, eventually exposing the optic nerve. The optic nerve and adjacent posterior ciliary blood vessels are carefully

clamped by curved hemostat, and transected by curved Metzenbaum or enucleation scissors immediately in front of the hemostat (Fig. 4.12e). With the posterior attachments free from the globe, further medial rotation permits incision of the medial extraocular muscle insertions and periorbital fascia, freeing the globe, lacrimal gland, conjunctivae, and nictitating membrane ‘en mass’ from the orbital wound (Fig. 4.12f). A sterile silicone sphere with its surfaces scarified by several incisions can be inserted at this time. Closure is accomplished in four layers, including the endorbita, septum orbitale, subcutaneous tissues, and skin (Fig. 4.12g). Portions of endorbita can be apposed with 2-0 to 4-0 simple interrupted absorbable sutures to secure the intraorbital prosthesis and reduce the dead space for serum collection. The septum orbitale, located in the deeper aspects of the eyelids, is apposed with 2-0 to 4-0 simple interrupted or horizontal mattress absorbable sutures. The subcutaneous layer is apposed with 2-0 to 4-0 simple interrupted absorbable sutures. The eyelid skin is apposed with 2-0 to 4-0 simple interrupted non-absorbable sutures.

Evisceration with intraocular prosthesis in small animals Evisceration is an attractive alternative to the enucleation procedure. The procedure, like the enucleation technique, treats blind and painful eyes, removes the need for topical and systemic medications, but provides improved cosmesis. In the evisceration procedure, the entire intraocular contents are removed through a scleral or limbal incision, leaving only the fibrous tunics of the cornea and sclera. Into this corneoscleral shell is inserted a sterile silicone sphere, and the scleral or limbal wound apposed. The usual results are a painless and cosmetically acceptable eye that often requires no medical therapy, has movement, and often shows no obvious ophthalmic disease. The primary indication for evisceration is end-stage primary glaucoma, which has become medically non-responsive, with enlarged and painful globes. Globes with secondary glaucoma associated with septic panophthalmitis and intraocular neoplasms are not candidates for evisceration, and should be treated by the enucleation procedure. Severely lacerated globes with loss of intraocular tissues are occasional candidates for evisceration with intraocular prosthesis, assuming infection is not present. Evisceration with intraocular prosthesis should be delayed or not performed in eyes with major corneal diseases, including deep ulceration and low tear production. Weakened corneas may not be able to accommodate the direct posterior contact with the intraocular implant. Some failures following evisceration with intraocular prosthesis have been associated with recurrence of the preoperative ophthalmic disease, especially unsuspected intraocular neoplasia and mycotic infections. Ophthalmic prosthetic devices have been described in the veterinary literature since the latter part of the nineteenth century. Most of the ophthalmic devices attempted in animals were employed after removal of the eye, and were positioned either in the remaining conjunctival space or within the orbit. The shell-type artificial eyes require daily maintenance, and orbital and conjunctival tissue contracture usually eventually extrudes these devices. Simpson reported on

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G Fig. 4.11 Enucleation – transpalpebral approach: In this technique the globe is removed with the eyelids sutured or clamped together. (a) The palpebral fissure is closed by suturing the eyelids together with a continuous non-absorbable suture. Alternatively, the eyelids can be clamped together by Allis or towel forceps. (b) The eyelid skin and orbicularis oculi muscle layers are incised for 360 to the level of the tarsoconjunctiva. The incision is usually about 6–8 mm from the eyelid margins to avoid the bases of the meibomian glands. (c) With the sutured eyelids clamped by Allis forceps, the dissection is continued by small curved Metzenbaum scissors around the conjunctival fornices and onto the globe. (d) Once the sub-Tenon’s space is entered about the globe, the different extraocular muscle insertions are isolated and transected. Hemorrhage is usually minimal as long as the surgical plane remains in the sub-Tenon’s space. (e) Once the posterior orbit is entered, the optic nerve is carefully isolated, clamped by a curved hemostat, and incised by curved scissors posterior to the clamp. (f) The first of two layers of closure consists of apposition of the orbital septum with simple interrupted or simple mattress absorbable sutures. (g) The second and last closure is apposition of the eyelid and orbicularis oculi muscle layer with simple interrupted non-absorbable sutures.

intrascleral implants in dogs in 1956, but unfortunately excised the cornea to permit visualization of the prosthesis. Recurrent conjunctivitis in most of these dogs required intermittent topical antibiotics, and local infections often resulted in eventual prosthesis extrusion. Following encouraging studies on intrascleral prostheses in dogs by Magrane and Helper, the silicone (Jardon Eye Prosthetics Inc., Southfield, MI) and methyl methacrylate (Storz Instrument Company, St Louis, MO) spheres have been found to be non-painful, similar to the normal eye in appearance, non-toxic, non-antigenic, easily implanted, inexpensive, and approximate the intraocular volume. Sphere size  1 mm is determined by caliper measurement of the horizontal corneal diameter. In adult dogs, the sphere diameter size usually ranges from 18 to 22 mm. When globe size has been increased by glaucoma, the fellow normal eye cornea is measured to determine the optimal sphere size.

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After implantation in glaucomatous globes, the elastic sclera and cornea will reduce in size over 1–3 months to conform to the sphere size. Available in different colors, the black sphere is recommended for dogs and the yellow sphere may be used in cats. A vertical pupil can be tattooed on the sphere for the cat. The silicone sphere can be sterilized by steam or gas if properly aerated. Sterilization of the methyl methacrylate spheres is by gas or by boiling. Chemical sterilization of these spheres is not recommended. After draping, an eyelid speculum is inserted between the upper and lower eyelids to increase surgical exposure. A lateral canthotomy may be used for additional exposure (Fig. 4.13a). With tenotomy or strabismus scissors, a 6 mm limbal-based conjunctival flap is constructed for 180 , usually from the 9 to 3 o’clock position. The bulbar conjunctiva is carefully and bluntly separated from the underlying Tenon’s capsule and sclera (Fig. 4.13b). Hemostasis is

Evisceration with intraocular prosthesis in small animals

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G Fig. 4.12 Enucleation – lateral approach: In this procedure the globe is removed from Tenon’s capsule starting at the lateral canthus. (a) A lateral canthotomy is performed by tenotomy scissors. (b) At the lateral canthus and using curved small Metzenbaum scissors, the skin–muscle and the tarsus–conjunctiva layers of the upper and lower eyelids are separated. (c) The eyelid skin–orbicularis oculi layer is incised for 360 by scissors to expose the deeper tarsoconjunctiva. (d) The skin–muscle layer and eyelid margins are clamped by Allis forceps, and the globe is rotated medially to incise the lateral canthal attachments. (e) With deeper retrobulbar dissection and incision of the lateral rectus and retractor oculi muscle insertions, the globe can be rotated medially to expose, clamp, and transect the optic nerve. (f) Continued rotation of the globe exposes and permits incision of the remaining medial extraocular muscle insertions, the medial canthal ligament, and the conjunctiva–nictitating membrane. (g) Closure is accomplished in four layers including parts of the endorbita, septum orbitale and subcutaneous tissue with simple interrupted absorbable sutures, and eyelid skin layer with simple interrupted non-absorbable sutures.

maintained by point electrocautery. The sclera is incised at the 12 o’clock position with a Beaver No. 6400 microsurgical blade, about 4 mm posterior and parallel to the limbus (Fig. 4.13c,d). Scleral tissues will usually hemorrhage and judicious point electrocautery is usually necessary. The scleral incision is extended both medially and laterally with tenotomy scissors to about 180 . The scleral incision must be 1–2 mm larger than the sphere diameter to accommodate the insertion of the device. Alternatively, the anterior chamber may be entered through a limbal incision. The limbal incision is associated with less hemorrhage than the scleral approach, but may be associated with more frequent postoperative corneal complications. The globe is eviscerated using the lens loop posteriorly and cyclodialysis spatula or an iridal spatula anteriorly to bluntly separate the anterior and posterior uveal tract from the limbus and sclera (Fig. 4.13e). The lens loop may be the most successful instrument and cause the least hemorrhage. With slight traction on the iris, the entire anterior and posterior uvea, lens, vitreous, and retina are removed (Fig. 4.13f). The intraocular space is gently flushed with saline or lactated Ringer’s solution to remove

all blood clots and any remaining intraocular tissues (Fig. 4.13g). Excessive flushing is not recommended as damage to the corneal endothelium may result. A sterile premeasured silicone sphere, rinsed in saline, is carefully introduced into the fibrous tunics with the Carter sphere holder and introducer (Fig. 4.13h–k). Once the sphere is in position, an additional flush with saline of the area is performed. The scleral incision is apposed with 5-0 to 6-0 simple interrupted or continuous absorbable sutures (Fig. 4.13l). The bulbar conjunctiva and Tenon’s capsule are apposed with a 5-0 to 6-0 simple continuous absorbable suture. The lateral canthotomy is closed with 4-0 non-absorbable figureof-eight and interrupted mattress sutures. Complete temporary tarsorrhaphies are often used after the evisceration procedure to protect the cornea for 10–14 days postoperatively. Topical and systemic antibiotics are administered immediately after surgery and continued for 5–7 days. If the cornea develops a central ulceration postoperatively, a bulbar conjunctival graft should be performed as corneal healing in these eyes appears slow and impaired. Penetrating corneal ulcers often necessitate enucleation.

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Fig. 4.13 Evisceration with intraocular prosthesis. In this technique all of the intraocular tissues are removed, and a silicone sphere is introduced into the globe consisting of only the cornea and sclera. (a) A 5–10 mm lateral canthotomy is performed by strabismus or Steven’s tenotomy scissors to increase the size of the palpebral fissure and facilitate surgical exposure. (b) After incision of the bulbar conjunctiva and Tenon’s capsule 4–6 mm from the limbus by tenotomy scissors, the sclera is exposed for about 180–200 . (c) The sclera is incised with the Beaver No. 6400 microsurgical blade for approximately 140–180 . (d) Incision of the sclera results in variable amounts of hemorrhage which is controlled by point electrocautery. (e) A lens loop (or blunt spatula) is inserted into the subscleral space, or between the sclera and the anterior and posterior uvea tracts. All of the intraocular tissues are gently separated from the sclera. Hemorrhage is to be expected. (f) With gentle traction, the iris, ciliary body, lens, vitreous, and retina are protracted from the anterior globe. (g) Intraocular hemorrhage is expected as the intraocular tissues are gently retracted from the corneoscleral tunics. The shell, consisting of the cornea and sclera, is gently flushed with sterile saline to remove any remaining intraocular tissues and clots. (h) The Carter sphere holder and inserter. A yellow sphere is held by the instrument’s tips and is usually used for eviscerations in the cat. A black sphere is recommended for the dog. (i) With the Carter sphere holder and inserter, a premeasured sterile sphere (the diameter is usually 1 mm less than the horizontal corneal diameter) is placed into the fibrous tunic shell. (j) Intraoperative appearance of the Carter sphere holder and inserter. During the insertion of the sphere into the globe, the instrument inserts the sphere while retracting the edges of the scleral wound. (k) Intraoperative appearance of the eye after intrascleral yellow prosthesis placement. Some hemorrhage still remains in the anterior chamber. (l) The two layer closure consists of apposition of the scleral and the bulbar conjunctival wounds with simple interrupted absorbable sutures. Often a temporary complete tarsorrhaphy is then performed to protect the cornea.

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Enucleation procedures in large animals and special species

Exenteration in small animals Exenteration is the complete removal of all of the orbital tissues, including the globe, nictitating membrane, conjunctivae, lacrimal gland, zygomatic salivary gland (in the dog), and extraocular muscles. In some patients, some of the orbital periosteum can also be removed. The indications for exenteration include orbital neoplasia, medically non-responsive orbital infections, and extensive intraocular neoplasia that has extended into the orbit. The surgical procedure is very similar to the transpalpebral enucleation procedure except the surgical dissection is along the orbital walls, external to the extraocular muscles. More hemorrhage is associated with this procedure. Apposition of the eyelids after complete removal of the orbital contents is similar to the other enucleation procedures. Systemic antibiotics should be administered postoperatively for 5–7 days.

Enucleation procedures in large animals and special species Orbital surgery in the horse Retrobulbar nerve blocks Retrobulbar or orbital local anesthesia injections are used to reduce globe and nictitating membrane movement, and to block or lower corneal and conjunctival sensation for standing procedures such as eyelid lacerations, nictitating membrane excision, corneal foreign body removal, iris cyst laser ablation, anterior chamber or vitreous injections or aspirations, and enucleations in standing horses and horses under general anesthesia. Retrobulbar nerve blocks are used to decrease the depth of general anesthesia required for orbital, corneal, and intraocular surgery. Two techniques are used in horses (see Fig. 3.8, p. 45–46). The skin of the orbital fossa just caudal to the posterior rim of the orbit is prepared for aseptic surgery, and a 6.25 cm, 22 g spinal needle is inserted just caudal to the posterior aspect of the bony orbital rim. The needle is inserted until it reaches the extraocular muscle cone. This is detected by

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slight dorsal movement of the eyeball. With the needle in position, 10–12 mL of 2% lidocaine is injected. Slight exophthalmos usually occurs. Anesthesia takes effect in about 5–8 min and lasts 1–2 h. The second technique is performed by curving the needle slightly and placing it through the conjunctival fornices using a four-point or a two-point retrobulbar block. With a two-point block, usually 4–8 mL of lidocaine is injected per site. When a four-point block is used, the injection volume of local anesthetic is 2–6 mL per site

Surgical techniques Enucleation Enucleation is the surgical removal of the globe, third eyelid, and conjunctivae. In most cases the eyelid margins and meibomian glands are removed and the skin sutured to cover the open orbit.

Indications Enucleation is indicated for the removal of a blind, painful, deformed or traumatized eye. The subconjunctival approach is used for corneal disease, glaucoma, and phthisis bulbi (Fig. 4.14). Removal of an equine eye is considered major surgery, and is only rarely considered in a standing non-anesthetized animal. When only one general anesthesia episode is feasible or affordable, and the fellow eye is sighted, enucleation may be the treatment of choice for advanced or painful ocular disease. Enucleation should not be considered a failure of ophthalmic care, but rather the appropriate and planned treatment for some ophthalmic disorders. In horses determined to be at high risk for complications from anesthesia or recovery, those not amenable to frequent medications, and for those cases in which additional expenses are not possible, enucleation is a rapid therapy to restore comfort and prevent further sequelae from disease. It is important to ensure that anesthesia and the recovery phase are not a greater risk than the benefit of surgery. Retrobulbar nerve blocks can dramatically reduce the depth of general anesthesia required for enucleation or facilitate enucleation in a heavily sedated standing horse.

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Fig. 4.14 Patient candidates for enucleation in the horse. (a) Septic panophthalmitis with exudative retinal detachment in an adult horse. (b) Advanced medial canthal and orbital squamous cell carcinoma in an adult horse.

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The client should be educated as to the alternatives to enucleation, expected costs associated with therapy and surgery, expected appearance after enucleation, and possible complications of anesthesia and surgery; all these should be well understood before proceeding. Cosmetic options for the horse should be explained before proceeding with enucleation. These will be discussed later in this section. There are two basic approaches to enucleation in the horse: the subconjunctival approach and the transpalpebral approach. The subconjunctival approach requires less time to perform and usually results in much less hemorrhage. It is used for cases of glaucoma, corneal ulcers, corneal neoplasia, irreparable corneal or scleral tears, refractory uveitis, and endophthalmitis. It is also the better cosmetic result of the two approaches. The subconjunctival technique is used when a cosmetic shell is placed to maintain the integrity of the eyelid margin. The transpalpebral approach is recommended in patients with severe corneal infections, large corneal, third eyelid, or conjunctival neoplasia. This technique creates a larger soft-tissue defect of the orbit than the subconjunctival approach. An orbital prosthesis may be placed with either technique, although a larger silicone sphere is needed with the transpalpebral approach.

Subconjunctival enucleation If severe infection or extensive neoplasia is present, a closed transpalpebral approach is the preferred surgical technique. The subconjunctival approach results in less postoperative discomfort because fewer tissue planes are traversed. Subconjunctival enucleation is initiated by placement of an equine eyelid speculum or sutures to hold the eyelids open for the procedure. A minor lateral canthotomy is performed. The lateral canthus is crushed with hemostats for 0.5–1 min, and the skin and conjunctivae are cut with a blade or surgical scissors. The bulbar conjunctiva is infiltrated with 2% lidocaine, incised 5 mm caudal to the limbus with Steven’s tenotomy scissors, and a complete peritomy performed. The extraocular muscles are identified and isolated with a strabismus (muscle) hook. The muscles are incised near or at their attachment to the sclera, permitting free rotation of the globe. The retractor bulbi muscles attach more posteriorly, and are more difficult to visualize. They are incised somewhat blindly. A curved or angled hemostat is used to crush the optic nerve and associated vessels. The globe is removed and submitted for histologic examination. The orbit may be packed with sterile gauze or GelfoamW. Frequently a silicone sphere is cut to form a flattened anterior surface and placed in the orbital space to eliminate dead space after enucleation. The nictitating membrane and any remaining conjunctivae are removed. The orbital lacrimal gland is rarely identified and removed. The remaining orbital contents should be examined to ensure that all diseased tissue has been removed. Capillary hemorrhage is common but should not preclude examination of the orbit. The orbit should be flushed with dilute povidone–iodine. The orbital space may be packed with sterile gauze sponges or surgical GelfoamW. Infusion of antibiotic solution should be considered if the orbit is contaminated during the procedure. A surgical drain (Penrose) through the ventral orbit

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should also be considered in a contaminated surgical site. If the orbit is contaminated during surgery, an orbital prosthesis is usually not placed. After the remaining conjunctivae are excised, the eyelid margin is resected from lateral to medial. Usually 6–8 mm of eyelid is removed so that no meibomian gland material is left. Care is taken at the medial canthus to remove the entire medial canthal skin but not to incise the medial anguli oculi vein and artery deep to the medial canthus. If the upper or lower lacrimal canaliculus is visible, it is ligated with 3-0 to 4-0 polyglycolic acid sutures.

Transpalpebral enucleation The transpalpebral approach is preferred for large malignant neoplasms and for septic globes. The transpalpebral technique allows for complete separation of the globe from the orbit. After the eye and periocular tissue are prepared for aseptic surgery, the eyelids are sutured tightly with 2-0 or 3-0 nylon, in a Ford interlocking or simple continuous pattern, with the suture ends left long (Fig. 4.15a). Large hemostats or Allis tissue forceps are placed on sutures at each end of the eyelid fissure to provide identification and traction during the procedure. A full-thickness skin incision is made 6–8 mm from the eyelid margins. Tissue planes are then bluntly dissected to separate the skin from the tarsal layer. These tissue planes are a natural separation formed by a potential space from embryonic development. The separation is extended to the periorbital margin with caution to prevent perforating the tarsal layer and contaminating the orbit. The medial canthal ligament and lateral canthal attachments are cut with a surgical blade. Additional dissection will separate the globe from the orbital connective tissue (Fig. 4.15b). Extraocular muscles are dissected and excised. The optic nerve or optic cone is clamped with curved forceps or Carmalt forceps. A ligature may be paced around the optic cone and tightened if desired. The optic nerve is resected anterior to the clamp or about 0.5–2 cm from the globe. This technique naturally removes more orbital tissue than the subconjunctival approach. An orbital prosthesis is routinely placed. In addition, large non-absorbable sutures may be placed vertically, connecting the dorsal and ventral orbital rims to construct some support for the anterior orbit and permanent tarsorrhaphy (Fig. 4.15c,d).

Postoperative management Enucleation in the horse has a low incidence of complications, less than 10%. Complications occur when the entire nictitating membrane and gland are not completely removed, when the eyelid margins do not include the entire meibomian glands (meibomian glands extend about 6 mm into the eyelid skin), and when the bulbar and palpebral conjunctivae are not removed. Care must be taken to remove the eyelid margin at the medial canthus. Rarely is the orbital lacrimal gland removed during enucleation, but complications do not seem to occur. When drainage is observed from the suture line at the medial canthus, the differential diagnosis must be either the retained mucocutaneous junction of the eyelid margin at the medial canthus versus an infected orbit after enucleation. If retained eyelid margin in the medial canthus causes a draining tract, correction is to simply remove

Enucleation procedures in large animals and special species

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the eyelid margin and close the wound. If an infected orbit is present or an infected draining tract, it should be explored, debrided, flushed, and closed. The orbit may be flushed with an antibiotic solution and a dependent drain can be created through a stab incision in the ventral-most portion of the orbit. The drain tubing or Penrose drain is left in place for 24 h beyond the last purulent drainage or for 24 h of clear drainage. Some surgeons will use roll gauze soaked in povidone–iodine, placed in the orbit after debridement. The soaked gauze passes through a separate stab incision, and is held in place with a suture through the skin. A section of the gauze is removed daily for 2–5 days, or until the drainage becomes clear. The stab incision is sutured or allowed to heal by second intention.

Implants to improve postoperative appearance after enucleation Several techniques have been used to improve the cosmesis of the face and orbit following enucleation (Fig. 4.16).

Fig. 4.16 Postoperative appearance after subpalpebral enucleation in the horse. Note some concavity of the wound is present.

These range from the popular intraorbital silicone prosthesis to a conformer and corneoscleral shell.

Intraorbital silicone prosthesis An intraorbital silicone prosthesis may be inserted to prevent the sunken appearance of the orbit after removal of the entire globe in the subconjunctival enucleation procedure (see Fig. 4.13). The silicone prosthesis should be washed to remove surface oils and allowed to dry prior to sterilization. Usually steam sterilization is preferred. At surgery the sterile prosthesis is rinsed with sterile saline or dilute povidone–iodine solution prior to insertion into the orbit. The size of the prosthesis is selected to fill the orbit and approximate the size of the contralateral globe. The fellow eye may be measured prior to surgery to give a size estimate for the orbital prosthesis. Usual prosthesis sizes range from 40 to 48 mm diameter silicone sphere in adult horses (Jardon Eye Prosthetics Inc., Southfield, MI). A silicone orbital implant designed to prevent or decrease skin sinking after enucleation is also marketed by Veterinary Ophthalmic Specialties (Moscow, ID). The silicone prosthesis is rinsed or wiped with sterile saline or dilute povidone–iodine to remove any powder or dust. The anterior surface of the prosthesis is cut to flatten the anterior aspect of the prosthesis to reduce the prominent anterior curvature of the silicone sphere. Non-absorbable suture material is used to close the orbital tissue and the sphere incorporated into the suture pattern to prevent rotation and hold the prosthesis in place. Use of intraorbital implants is not recommended in horses enucleated for orbital infections or neoplasia. Following introduction into the orbit, the prosthesis is fixed in a stable position with 2-0 to 4-0 nylon or prolene shallow sutures, and incorporated into a meshwork or in the closure of the extraocular muscles or orbital connective tissue. A layer of tissue is closed between the prosthesis

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and the skin with 3-0 to 4-0 absorbable sutures, usually in a continuous or interrupted mattress suture pattern. Closure is usually accomplished in several layers. If no prosthesis is introduced, the periorbita may be partially approximated with an interlocking mesh of non-absorbable sutures to prevent sinking in of the skin postoperatively (see Fig. 4.15c). Retracting the skin and subcutaneous tissue will aid in placement of this mesh suture. The subcutaneous tissue is closed with 2-0 to 4-0 absorbable sutures in a Ford interlocking or simple continuous pattern. Some surgeons prefer a simple interrupted or cruciate pattern. Skin is closed with an interrupted cruciate or simple interrupted pattern. To avoid suture removal, an intradermal skin closure in a continuous pattern using 4-0 to 5-0 VicrylW has been used. Tetanus prophylaxis should be verified or given at or prior to surgery. Postsurgical swelling is usually minimal but will increase during recovery as the systemic blood pressure increases. Cold compresses followed by warm compresses 24 h later are used if the horse will tolerate them. Pressure bandaging of the face is rarely used.

Intrascleral silicone implants Evisceration of the globe and implantation of an intraocular silicone prosthesis (ISP), also termed an intrascleral silicone prosthesis, is a procedure used in horses for blind, painful eyes, chronic glaucoma, early stages of phthisis bulbi, and for corneal and sclera lacerations that have a poor prognosis for surgical correction. An ISP requires a single surgical episode, and in most cases is more cosmetic than enucleation. It is considered less cosmetic than placement of a scleral shell or an artificial globe, which requires multiple anesthetic and/or surgical procedures. Many clients accept an ISP to be more cosmetic and preferable to removal of the eye or a phthisical globe. Clients should be educated to the fact that corneal disease can occur and diseases of the eyelid margin and nictitating membrane are possibilities that will require therapy. Eyes with pre-existing corneal disease should be regarded as being at higher risk for keratitis and ulceration following ISP. The presence of corneal disease at the time of surgery increases the risk of postoperative complications. However, an intrascleral silicone prosthesis can be implanted successfully in horses with corneal lacerations. A conjunctival advancement or pedicle flap should be considered at the time of surgery, but may diminish the cosmetic appearance. Diseases (including neoplasia) that involve the eyelid margin, nictitating membrane, and conjunctivae can occur following ISP since these structures are not removed.

Evisceration and intrascleral silicone prosthesis Evisceration is the removal of the intraocular contents: aqueous, lens, uveal tract, retina, and vitreous, with preservation of the fibrous tunic, or cornea and sclera. Careful surgical preparation is performed. Eyelashes are trimmed, periocular skin is washed with baby shampoo, and nasolacrimal ducts are flushed with dilute povidone–iodine. The skin is prepared for aseptic surgery, and the conjunctival fornices are flushed with dilute povidone–iodine, swabbed with

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sterile cotton-tipped applicators, and flushed with sterile saline. With the horse under general anesthesia, sensory nerve blocks of the eyelids are performed along with a retrobulbar block. Topical proparacaine and topical 10% phenylephrine are applied at 5-min intervals, beginning about 20 min prior to surgery. A subconjunctival line block of 2% lidocaine is performed from about 3 to 9 o’clock, using approximately 0.5 mL of lidocaine. A self-adhesive drape or dental dam is used to avoid contamination of the surgical site. A conjunctival flap is raised for about 160–180 , 6–8 mm posterior to the limbus. Wet field or disposable ophthalmic cautery is used to cut through Tenon’s capsule; blunt dissection and cautery are used to expose the sclera. The sclera is scored with the cautery unit and incised full thickness to the uveal tissue using a No. 6400 microsurgical blade. Care should be taken to incise the sclera without perforation of the underlying uveal tissue. If it is necessary to improve exposure to remove uveal contents or to insert the silicone sphere, a T-shaped incision is performed by scissors. To remove the ciliary body and iris, a cyclodialysis spatula is inserted anteriorly between the sclera and the uveal tissue to break the attachments of the iris at the iridocorneal angle. A lens loop is used to separate the uveal tissue from the sclera posteriorly, and to separate the choroid and retina from the sclera. Two non-toothed forceps or hemostats are used to grasp and remove the uveal tract. Caution is exercised to prevent damage to the corneal endothelium. The uveal tissue is placed in fixative for histopathologic evaluation. The remaining intraocular contents are removed, the intraocular space is swabbed with moistened cotton-tipped applicators, and the fibrous shell is flushed with sterile saline. Complete removal of the lens should be verified. Efforts are made to remove the entire uveal tract, but retained remnants of uveal tract do not appear detrimental. An intraocular silicone prosthesis is usually selected after measuring the normal cornea with calipers and adding 1–2 mm. In most adult horses the silicone sphere should be 36–40 mm in diameter. The prosthesis is rinsed in sterile saline or residual powder is removed by wiping the prosthesis with saline or dilute povidone–iodine solution. The silicone sphere is introduced with care to avoid touching the eyelids or conjunctiva. The fit is assessed by apposing the edges of the scleral incision. Some surgeons will use light suction to remove blood from the fibrous cavity. The anterior surface of the prosthesis may be cut, trimmed, and flattened to provide a more cosmetic result and to decrease contact with the corneal endothelium. The scleral incision is closed with 4-0 to 5-0 polyglactin 910 in an interrupted or simple continuous pattern. The full extent of the incision should be visualized and both ends closed carefully to prevent dehiscence. The conjunctiva and Tenon’s capsule are closed with a continuous pattern, ensuring that the scleral incision is completely protected. The lateral canthoplasty, if performed, is closed in two layers. A subpalpebral lavage system may be placed to apply topical antibiotics after surgery. A temporary tarsorrhaphy is performed to reduce exposure and to protect the cornea and scleral closure. The globe is lubricated with OptixcareW gel. Postoperative medication includes topical and systemic antibiotics and systemic anti-inflammatory agents,

Enucleation procedures in large animals and special species

usually flunixin meglumine (BanamineW; Schering-Plough, Kenilworth, NJ). The tarsorrhaphy sutures are removed in 3–4 days. Persistence of, or an increase in, ocular discharge indicates the need for ophthalmic evaluation, possible culture and sensitivity testing, and staining the cornea with fluorescein dye. Corneal ulceration is the most common complication. Less frequent complications include: dehiscence of the surgical site; endophthalmitis, either septic or powder induced; or severe periocular swelling if traumatic dissection occurred. Many corneas vascularize and scar within a few weeks after surgery and may not appear very cosmetic. With time, if pigmentation results, the globe is more cosmetic.

the exposed intrascleral implant. Later studies succeeded by using a silicone sphere placed within the ocular or corneoscleral tunics. Gilger and associates reported use of a custom-made hydroxyapatite orbital implant after enucleation of the eye in a horse (Fig. 4.17). The corneoscleral prosthesis was fitted over the orbital implant. The hydroxyapatite orbital implant permits vascular and fibrous tissue growth from the host into and over the implant, thereby decreasing the chance of infection and implant extrusion. The extraocular muscle insertions can be attached to the orbital implant to provide mobility.

Orbital exenteration in the horse Cosmetic corneoscleral conformer, scleral cosmetic shell, and corneoscleral prosthesis Corneoscleral conformers or extrascleral shell implants are made by ocularists from methyl methacrylate, porcelain, or hydroxyapatite to fit to and cover a phthisical globe or a disfigured eye. The surface is painted by the ocularist from a photograph of the fellow eye and the prosthetic shell is fitted into the conjunctival sac. The eyelids and third eyelid help to fix the conformer in the desired location. The relatively high costs and frequent cleaning of the prosthesis are limiting factors in their use. The results are very cosmetic and most owners are quite happy with the outcome. Extrascleral shell conformers are available from Jardon Eye Prosthetics Inc. (Southfield, MI) or can be individually made for horses by Dallas Eye Prosthetics (Dallas, TX). Early artificial eyes or cosmetic globes (often constructed of glass or ceramic material) inserted into the sclera after evisceration of all the intraocular tissues and removal of the entire cornea failed in horses because of infection eventually extending between the sphere and the host’s sclera. This chronic infection ultimately resulted in extrusion of

A

Exenteration in horses is a surgical technique designed to remove large tumors from the orbit that are unresponsive to other forms of therapy such as radiation therapy or chemotherapy. Systemic antibiotics and flunixin meglumine are given before surgery. Tetanus prophylaxis should be verified or administered prior to surgery. With this technique, the entire orbital contents are surgically removed, including the globe and the periorbita. The globe is removed by enucleation and then periosteal elevators are used to remove the periorbital fascia. Care must be exercised to avoid breaking into a paraorbital sinus. The remaining orbital tissue is removed using electrocautery and sharp dissection. Bleeding should be controlled with cautery and ligatures. An orbital prosthesis is usually not placed when a large neoplasm is excised. The remaining eyelid skin is sutured to cover the open socket. If inadequate skin remains, the facial skin is undermined and walking sutures are used to cover the defect. If excessive skin must be removed, a skin flap or graft can be used. In rare cases, if a large amount of eyelid and facial skin must be sacrificed, the socket may be allowed to granulate and epithelialize.

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Fig. 4.17 Intraorbital implants and corneoscleral conformers are used in the horse to reduce wound disfigurement and attempt to compensate for, at least, some of the tissue loss from the enucleation procedure. (a) The hydroxyapatite intraorbital implant and corneoscleral conformer (generally constructed by an ocularist) for the horse. The extraocular muscle insertions may be attached to the implant, thereby providing globe motility. (b) Postoperative appearance in this type of implant in a horse. (Both photographs courtesy of Brian Gilger, North Carolina State University.)

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Postoperative management after exenteration Pressure bandages over the orbit are used to reduce swelling. Systemic antibiotics and flunixin meglumine are continued. If a sinus is damaged or entered during the procedure it may require trephination, drainage, and lavage.

Orbital surgery in the bovine Enucleation of the bovine eye In adult cattle, the most common enucleation technique is the transpalpebral approach. With this technique more of the orbital contents are removed than with a transconjunctival or subconjunctival approach to enucleation. Frequently, removal of the bovine eye is done for economic reasons for neoplasia of the third eyelid (nictitating membrane) or eyelids, when the eye or globe is normal (Fig. 4.18). In many cases it is easier and preferable to remove the eyelid mass by ‘H-plasty’ in cattle, or to remove the third eyelid when it is affected rather than remove the entire globe, or in some cases perform an exenteration when the globe itself is intact and visual. Excision of eyelid squamous cell carcinoma (SCC) in cattle is commonly performed, and is certainly preferable to enucleation or exenteration when there is no involvement of the globe or the bony orbit. Other forms of therapy for eyelid neoplasia should be considered before enucleation of a normal eyeball. These include cryotherapy, hyperthermic therapy, chemotherapy, immunotherapy, and radiation therapy. Chemotherapy might include 5-fluorouracil (5-FU) or intralesional injections of cisplatin in sesame oil injected every 2 weeks for 8 weeks (four treatments). Immunotherapy has also been used for SCC in cattle. A mycobacterium cell wall immunostimulant has been used successfully in cattle with SCC; however, a major drawback was that it converted the animals into tuberculin reactors. A phenol–saline extract of bovine SCC led to regression of lesions following intramuscular injections. Immunotherapy with bacille Calmette–Gue´rin (BCG) may be considered as well as immunomodulation with oral cimetidine for eyelid neoplasia. Investigation of therapeutic results for SCC in cattle is hindered by the suspected relatively high incidence of spontaneous regression of these tumors. In other cases, exenteration of the orbit may be performed for uveitis, septic panophthalmitis, trauma to the globe, and

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severe ocular trauma that are beyond reasonable repair. Enucleation may be inappropriate if the neoplastic process involves the bony orbit or has metastasized to regional lymph nodes. The veterinarian should examine the oral cavity and teeth to determine the animal’s age and perform rectal palpation to determine pregnancy status. Older age and non-pregnancy may alter the feasibility of enucleation from an economic standpoint. The sale value for breeding use seems to decrease after the removal of one eye. An animal should never have both eyes removed, unless used as a pet, and this practice is questionable from a humane standpoint. In some cases, one-eyed cattle may do poorly in a feedlot situation.

Anesthesia and surgical preparation Most enucleations are performed with the animal standing in a head catch or chute. The head is securely restrained with a halter and nose lead, or a head board restraint device. Intravenous sedation and analgesia are commonly administered. The head is pulled to the opposite side of the chute from the eye to be removed, allowing adequate positioning and exposure for the surgeon. Usually the hair is clipped from the surgical site using a No. 40 clipper blade on a small animal electric clipper. If large amounts of necrotic or neoplastic tissue are present in the surgical area, this should be trimmed with scissors prior to scrubbing the site for surgery. Some surgeons now elect to use sterile drapes for the surgical area. The surgeon must be certain that the diseased eye is being removed and not the normal eye. Intravenous mild sedation is used in some cattle. For standing surgeries, xylazine (0.05 mg/kg IV) and butorphanol (0.02 mg/kg IV) are used. The addition of a low dissociative dose of ketamine (0.1 mg/kg IV) has been used to assist with fractious patients. The combination of xylazine, butorphanol, and ketamine has been called the ‘Ket-Stun’ technique. Anti-inflammatory therapy, flunixin meglumine (1 mg/kg IV), immediately before surgery appears adequate for most enucleation procedures. Local anesthesia is used to infiltrate the retrobulbar tissues. A four-point retrobulbar block is commonly performed by injecting through the lower and upper eyelids and at the medial and lateral canthi. A slightly curved, 8–10 cm, 18–20 g needle is directed toward the posterior orbit and 10–20 mL of lidocaine injected. An alternative is

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Fig. 4.18 Bovine candidates for enucleation. (a) Panophthalmitis with corneal rupture in a cow after injury. (b) Intraocular squamous cell carcinoma in a cow. Tumor apparently originated from the lateral limbus. (c) Extensive orbital squamous cell carcinoma is a 10-year-old Holstein cow.

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to mix a 4:1 injection solution of 0.5% bupivacaine and 2% lidocaine containing 1:100 000 adrenaline (epinephrine). When the retrobulbar tissue has been adequately anesthetized the eye will appear exophthalmic, the pupil will be dilated, and corneal sensation will be absent. Some surgeons have favored the Peterson eye block for this procedure, but it has mostly been replaced with the four-point block, due to unpredictable anesthetic traits of the Petersen method.

Surgical technique Immediately following surgical preparation, the surgical site is draped. Covering the entire head with the drape will provide a more sterile field and may aid in restraint. The eyelids are held together with two or three Backhaus towel clamps. This decreases contamination of the surgical field and the towel clamps are used for light traction during dissection. An alternative method is to use nylon suture material to close the eyelids with the ends left long enough to provide traction during the procedure. A transpalpebral incision is made around the eyelid margins, leaving as much normal tissue as possible. If adequate normal eyelid is present, the incision is usually about 1 cm from the eyelid margins. If additional abnormal eyelid tissue must be removed, maintaining enough normal skin to close the wound is imperative; alternatively, periorbital skin should be undermined for closure without tension on the suture line. The ventral skin incision and dissection are performed first to decrease hemorrhage from the upper eyelid obstructing the surgeon’s view of the surgical field. Dissection is continued for 360 using sharp and blunt methods. This is usually completed with a scalpel blade and large Mayo or serrated surgical scissors, or large curved surgical scissors. The dissection is continued posteriorly to the caudal border of the orbit. Dissection is done in a lateral and posterior fashion to avoid cutting through the conjunctiva. The extraocular muscles, orbital fat, lacrimal gland, conjunctiva, globe, nictitating membrane, and eyelid margins are excised. If the enucleation is performed for neoplasia, the surgeon must be certain that all eyelid, conjunctival, and retrobulbar neoplastic tissue has been satisfactorily removed. When enucleation is performed for non-neoplastic and non-endophthalmitic conditions, more of the retrobulbar tissue may be left in place. This will reduce the amount of postoperative dead space, intraoperative hemorrhage, and the sunken appearance of the orbital skin after surgery. Once the optic nerve and vessels of the optic stalk are isolated, traction on the globe should be minimal and twisting of the globe should be avoided. Contralateral blindness is a consideration in most species when enucleation is performed. If excessive traction or twisting of the globe occurs during removal, these traction forces are transmitted to the optic chiasm and can lead to damage of the chiasmal axons, resulting in blindness or visual field loss in the remaining good eye. The optic nerve and associated blood vessels are clamped with a right-angled forceps, enucleation forceps, large hemostat, Carmalt forceps, or a similar instrument. The blood vessels and optic nerve may be ligated or allowed to clot naturally or by pressure. The surgeon should gently palpate the orbit to be certain that all abnormal tissue has been removed. After removal of the globe a large amount of dead space is usually present. The orbit and retrobulbar

space will fill with blood. This clot will organize during the following few weeks, leaving a depression and sunken appearance to the face. An orbital prosthesis can be placed after surgery as is recommended in horses and small animals. A silicone sphere can be used without carving or a surgical blade may be used to flatten the front of the prosthesis in cattle. Another option to decrease the amount of sunken tissue is to ‘weave’ a non-absorbable suture across the orbit beneath the skin. Three-0 to 4-0 nylon or prolene would work well, if cosmesis is a concern. Some veterinary surgeons elect to pack the orbit with sterile gauze (10  10 cm) sponges immediately after the globe and orbital structures have been removed; the number of sponges packed into the orbit should be known to the surgeon. The gauze sponges are removed and counted prior to tying the final skin sutures. All sponges must be removed from the orbit. In some cases roll gauze may be packed into the orbit and removed at the end of surgery. Many surgeons elect to pack the orbit only if hemorrhage is considered excessive or uncontrollable by other means. Often skin closure is the only suture used in cattle enucleations. Frequently the skin is closed with a non-absorbable suture (No. 3 nylon) in a variety of patterns. Suture patterns used for skin closure in enucleation in cattle include the Ford interlocking, cruciate, simple continuous, and simple interrupted patterns. If a continuous pattern is selected, it may be fortuitous to use a single simple interrupted suture in the medial canthus, if by chance dependent drainage is needed, and the single suture can be removed easily. Nylon or prolene may be used for skin closure. In the past polymerized caprolactam (VetafilW) was used for this closure by many food animal veterinarians. The surgical site is re-examined in 10–12 days and the sutures are removed. Some surgeons now prefer to wait 14–21 days before suture removal. If drainage from the suture line or surgical site is present, the clinician may elect to remove the medial canthal suture, leaving the remainder of the skin sutures in place. If drainage, infection, or the need to remove only part of the suture line is predicted at surgery, then a simple interrupted pattern is recommended. Some veterinarians prefer to close the skin with absorbable sutures when suture removal will be problematic, such as in range conditions where it may be cost prohibitive and impractical to round up the animal for a suture removal. In such circumstances, 3-0 medium catgut or VicrylW is recommended, using a medium curved large animal needle and employing an interrupted horizontal mattress suture pattern using double strands of suture. Some veterinarians also choose to insert a sterile suspension or bolus of soluble antibiotic solution into the orbit at the end of surgery. This practice is met with controversy, since it is felt by some bovine surgeons that any material deposited in the orbit may become a nidus for infection, or may lead to inflammation or increased discomfort and drainage postoperatively, due to their chemical or caustic effects.

Postoperative management The degree of hemorrhage may alarm young or inexperienced surgeons. Many agree that the most appropriate hemostasis is a rapid surgery and pressure from the closed

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skin following surgery. Systemic antibiotics are recommended if infection is present at surgery.

Subconjunctival enucleation in the bovine A subconjunctival enucleation with the animal under general anesthesia may be performed in similar fashion to those performed in horses and small animals.

Evisceration of the globe and intraocular silicone prosthesis In some cases evisceration of the globe and implantation of an intrascleral silicone prosthesis is requested by the owner to maintain a more cosmetic face. This is uncommon in cattle, but may be used in valuable animals. This is most commonly performed after trauma to the globe and early phthisis bulbi formation.

Removal of prolapsed retrobulbar fat Prolapse of varying degrees of retrobulbar fat is an uncommon yet dramatic-appearing lesion in any animal. The diagnosis is usually made by visual assessment and digital palpation using a gloved and lubricated finger. In some cases the diagnosis is made by fine needle aspirate and cytologic examination. If surgical correction is elected, the prolapsed fat is removed following an auriculopalpebral nerve block and topical anesthetic with 5–10 drops of 0.5% proparacaine hydrochloride or ophthalmic tetracaine applied to the cornea and conjunctiva. In some cases anesthesia is facilitated by injection of a small amount of 2% lidocaine subconjunctivally at the incision site. Adequate restraint is necessary for ocular surgery in cattle. Most surgeries are performed with the animal standing in a squeeze chute, head catch, or stanchion, with the head restrained with a halter and nose lead, or head board restraint. The eyelids are prepared for aseptic surgery, and the conjunctiva and cornea are irrigated with dilute povidone–iodine solution. The conjunctival fornices are irrigated and swabbed with sterile cotton-tipped applicators. A conjunctival incision is made rostrally to the prolapsed fat with Steven’s tenotomy scissors (standard, curved, with blunt tips) or other small ophthalmic scissors. The fat is excised in toto. The conjunctival incision is closed to imbricate the area with a simple continuous pattern using 5-0 VicrylW. Some surgeons have used simple interrupted or mattress sutures of 3-0 to 4-0 polyglycolic acid. Topical antibiotic ointment is applied immediately following surgery.

Enucleation procedures in birds Removal of the globe in birds requires further modification of the enucleation procedures already presented. Avian globes are very large in relation to the surrounding bony orbit, and the extraocular space for surgery is quite limited. The avian sclera contains 10–18 small overlapping ossicles that form a bony ring and give shape to the avian eye. In owls these ossicles result in a tubular-shaped globe. In most hawks the globe has a globular shape. At least three different enucleation procedures have been developed for birds; selection depends on the globe shape. In owls a transaural enucleation procedure is recommended as these species have an extensive external ear opening. This method

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expands the palpebral fissure to permit removal of the large intact tubular-shaped globe. The second method, which can be used in any avian species, involves collapse of the globe to permit its removal through the palpebral fissure. The third technique is a modified evisceration method involving removal of the cornea and all of the intraocular tissues, but leaving the sclera and bony ossicles behind. A complete permanent tarsorrhaphy is then performed. Enucleation in birds, including owls and hawks, may be necessary after destruction of the eye and loss of vision following extensive trauma, intraocular infection, and noninfectious intraocular inflammation. As the avian eye is unusually large in relation to its face, enucleation involving complete removal of the globe results in considerable disfigurement. Leaving the sclera, as in the last modified evisceration method, results in less postoperative concavity of the eyelids. Birds have a very thin bony interorbital septum medially, and it should not be penetrated during surgery. As in any enucleation procedure, and even if globe is not removed intact, the contents should be examined histologically.

Transaural enucleation method for owls In the transaural enucleation approach for owls, the feathers over the auricular area and orbit are plucked, and the area prepared for aseptic surgery. The eyelids are retracted by two or more 4-0 silk stay sutures anchored in the eyelid margins or an eyelid speculum (Fig. 4.19a). An incision (indicated by a dotted line in Fig. 4.19a) is used to connect the lateral canthus to the anterior auricular margin. Using a No. 6400 microsurgical blade, the skin incision is extended through the lateral canthus and periorbital fascia to the anterior auricular margin to the junction of the tubular globe and the postorbital process (Fig. 4.19b). Hemostasis is achieved by point electrocautery. The lateral canthal and preaural skin are dissected free to expose the posterior aspects of the tubular globe (Fig. 4.19c). The subconjunctival dissection is continued under the periorbital fascia for 360 and extended posteriorly. A 12 o’clock incision of the periorbital fascia can provide additional mobility for the globe. With digital pressure carefully applied to the limbus, the No. 6400 microsurgical blade is used to create a space between the posterior globe and caudal orbit (Fig. 4.19d). Through this space, small tenotomy scissors are used to sever the globe from its extraocular attachments and transect the optic nerve (Fig. 4.19e). Once relieved of its attachments, the tubular globe is removed. Hemostasis is achieved by direct pressure and gauze sponges. After orbital hemostasis, the conjunctiva, nictitating membrane, and 2 mm of the entire eyelid margins are excised. Closure is started by reapposition of the anterior auricular margin with simple interrupted 5-0 to 7-0 absorbable sutures (Fig. 4.19f). The eyelids are then apposed using simple interrupted 5-0 to 7-0 absorbable sutures (Fig. 4.19g).

Globe-collapsing enucleation procedure for birds The globe-collapsing enucleation method can be used for any avian species. After general anesthesia and preparation for aseptic surgery, a small pediatric wire eyelid speculum is positioned to retract the upper eyelid, lower eyelid, and

Enucleation procedures in large animals and special species

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G Fig. 4.19 Enucleation in the bird: This procedure is complicated by both the shape and size of the globe, and the limited anterior orbital opening. In this method the anterior orbital opening is expanded by a lateral canthotomy that extends to the anterior auricular margin. This method is recommended for owls. (a) Two stay 4-0 silk sutures or an eyelid speculum is used to retract the upper and lower eyelids. The incision line (shown as a dotted line) extends from the lateral canthus to the anterior auricular margin. (b) The lateral canthus and skin are incised by No. 6400 microsurgical blade through the anterior auricular margin to the junction of the tubular globe with the postorbital process. The deeper conjunctiva and periorbital fascia are also incised. (c) By small curved tenotomy scissors, the skin is carefully dissected to expose the posterior aspects of the globe. The subconjunctival dissection is continued 360 to free the globe. (d) With digital pressure at the lateral limbus, the posterior globe is manipulated forward with the surgical blade. (e) Steven’s tenotomy scissors are inserted posterior to the globe to sever the optic nerve and any posterior attachments. The globe is delivered through this lateral incision. Hemorrhage is usually controlled by temporarily packing the orbit with sterile gauze pads. (f) After removal of the remaining conjunctiva and nictitating membrane and a 2 mm strip of eyelid margin, 5-0 to 7-0 absorbable simple interrupted sutures are used to appose the anterior auricular margin, the eyelids, and skin. (g) Immediate postoperative appearance. (Reproduced with permission from Murphy CJ, Brooks DE, Kern TJ, Queensberry KE, Riis RC 1983 Enucleation in birds of prey. Journal of the American Veterinary Medical Association 183:1234–1237.)

nictitating membrane. A lateral canthotomy, extending dorsolaterally to the anterior auricular margin, is performed using a No. 6400 microsurgical blade or small tenotomy scissors (Fig. 4.20a). The limbus is incised by scalpel or a combination of a scalpel and corneal scissors for 180 , and

a stay suture positioned in the center of the cornea for its manipulation (Fig. 4.20b). With curved tenotomy or strabismus scissors the bulbar conjunctiva, nictitating membrane, and periorbital fascia are incised 360 . The area deep to the auricular skin is carefully undermined (Fig. 4.20c). Mayo

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Fig. 4.20 Globe-collapsing procedure for enucleation in the bird. This technique can be used in any avian species. (a) After a fine wire eyelid speculum is positioned, a lateral canthotomy is performed by the No. 6400 microsurgical blade, extending dorsolaterally to the anterior auricular margin. (b) The limbus is incised for 180 and a stay suture is positioned in the central cornea. The conjunctiva, nictitating membrane, and periorbital fascia are incised for 360 . (c) The area medial to the auricular skin is also undermined. (d) By Mayo scissors inserted carefully between the subconjunctival and subscleral spaces, the sclera and scleral ossicles are incised. (e) Forceps are used to collapse the globe and permit access to the posterior globe. The optic nerve and posterior attachments are severed by scissors, and the globe is carefully removed. (f) After removal of the nictitating membrane, conjunctiva, and a 2 mm strip of eyelid margin, the eyelids are apposed with 5-0 to 7-0 absorbable simple interrupted sutures. (Reproduced with permission from Murphy CJ, Brooks DE, Kern TJ, Queensberry KE, Riis RC 1983 Enucleation in birds of prey. Journal of the American Veterinary Medical Association 183:1234–1237.)

scissors, carefully positioned between the uveal tract and sclera, are used to sever the sclera and its ossicles (Fig. 4.20d). With the dorsal sclera incised, forceps are used to collapse the globe. The extraocular muscle attachments and the optic nerve are severed by scissors, and the globe is removed from the orbit (Fig. 4.20e). Excessive traction on the globe as it is manipulated forward should be avoided to prevent damage to the optic chiasm. Hemostasis of the deeper orbit is achieved by direct pressure by gauze sponges and point electrocautery. The entire conjunctiva, nictitating membrane, and a 2 mm strip of eyelid margin are excised by tenotomy scissors. Closure of the remaining eyelids is accomplished by several 5-0 to 7-0 simple interrupted absorbable sutures (Fig. 4.20f).

Modified evisceration method for enucleation in birds This third method for enucleation in birds attempts to address the considerable disfigurement that occurs after removal of the entire globe. However, for this technique to be successful, the postoperative field must be sterile. Hence birds with possible panophthalmitis and intraocular neoplasia should not be considered candidates for this procedure.

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After placement of a small wire speculum, the peripheral cornea is incised for 360 , and the intraocular contents (including the uveal tract, lens, vitreous, and retina) are gently removed from the scleral shell by lens loop, spatula, and scissors. Hemostasis is achieved by direct pressure with surgical sponges and, if necessary, point electrocautery. The conjunctiva, nictitating membrane, and a 2 mm strip of the eyelid margins are excised by tenotomy scissors. The eyelids are apposed with 5-0 to 7-0 simple interrupted absorbable sutures.

Orbitotomy in small animals In the orbitotomy procedures, access to the interior of the orbit is gained with the eye in situ. The avenues include the anterior, lateral, dorsal, and oral approaches. The orbit in dogs can be approached from the frontal, dorsolateral, or lateral aspects, but the feline, equine, bovine, and bird orbits are usually entered frontally (through the palpebral fissure) and often with the globe already removed. The anterior approach enters the orbit through the bulbar conjunctiva or the eyelids beneath the conjunctival fornix. Both of these approaches have been

Orbitotomy in small animals

described as the initial part of the subconjunctival and transpalpebral enucleation procedures. The anterior orbitotomy approaches are the most useful for anterior orbital lesions. The lateral orbitotomy approach permits exploration of the canine anterior and posterior orbit, and is recommended for zygomatic gland diseases, zygomatic arch disease, and retrobulbar lesions lateral to or within the extraocular muscle cone. For maximal lateral orbital exposure, the center of the zygomatic arch can be temporarily transected and reattached at the conclusion of surgery. The dorsal orbitotomy approach provides primary exposure of the upper orbit, and is selected for dorsal retrobulbar, zygomatic process of the frontal bone, and parietal bone diseases. The canine and feline orbital floors are incomplete posteriorly, and limited access is available through an oral approach immediately caudal to the last molar tooth. As indicated earlier, a significant number of orbital masses involve the ventromedial orbit and, as a result, the surgical approach and visualization are difficult. Optimal exploration of the medial and ventromedial canine orbit usually requires removal of the globe and converts the orbitotomy procedure into an exenteration. The specific orbital surgical approach should be selected based on the location of the orbital disease. For instance, if the mass is isolated to the anterior medial or lateral orbit, anterior orbitotomy might provide the most useful route. If the primary lesion is confined to the lateral orbit or zygomatic salivary gland, lateral orbitotomy with temporary removal of the zygomatic arch may provide the best exposure. With a lacrimal gland mass, the recommended approach would be anterior transpalpebral orbitotomy. As previously noted, the feline orbit is only slightly larger than the globe, and surgical access to the retrobulbar space with the eye in situ is very limited. Limited lateral exposure can be attempted via an anterior transpalpebral or lateral orbitotomy approach.

Indications for orbitotomy The clinical indications for orbitotomy include the excision of an isolated inflammatory or neoplastic mass, biopsy of orbital tissue while under direct observation, ligation of major orbital vessels, orbital fracture fixation, orbital cytology and culture. The postoperative results after orbitotomies for the treatment of chronic inflammation (usually as focal abscesses or granulomas), benign tumors, masses and cysts of the zygomatic salivary gland, and the limited posterior extensions of neoplasms of the conjunctival and nictitating membrane are usually good. However, as indicated earlier, the majority of orbital neoplasms in the dog are malignant (about 90%) and most are primary (about 60–70%). In cats, over 90% of orbital neoplasms are malignant and most appear secondary. In addition to the limited barrier offered by the bony orbital walls, intraorbital masses tend to expand irregularly and exhibit indistinct borders. In large animals, most orbital neoplasms are malignant, and warrant a guarded prognosis. Before surgical intervention of the orbit is contemplated, one or more of the orbital diagnostic procedures should be performed in an attempt to define the limits and possible borders of the mass. As 4 of every 10 canine orbital neoplasms are secondary, examination of the nasal cavity and sinuses is imperative. A complete physical examination,

including chest and abdominal radiographs, complete blood count, blood chemistries, and urine analysis should be performed. Neoplastic tissues sometime appear grossly similar to adjacent orbital tissues. If the primary objective of an orbitotomy is to obtain tissue biopsies for diagnosis, or debulk a mass for possible treatment with chemotherapy and/or radiation, then an orbitotomy is recommended. The long-term survival rates for canine orbital neoplasms after diagnosis and attempts to remove by orbitotomy procedures are very low, and few dogs live beyond 3 years after diagnosis. If a primary orbital neoplasm is present in the dog, the most prudent surgical approach appears to be the exenteration procedure and removal of the eye. Preliminary results using the orbitectomy procedure in dogs with orbital neoplasms indicate better results and longer survival rates. The orbitectomy procedure involves excision of the globe, the remaining orbital tissues, and most of the orbital bones.

Lateral orbitotomy The lateral orbitotomy approach is usually performed in the area of the zygomatic arch. For optimal exposure, temporary removal of the zygomatic arch is recommended. Two different lateral orbitotomy procedures have been described. Unfortunately, in both approaches, some of the branches of the palpebral nerve that innervates the orbicularis oculi muscle (eyelid closure), the zygomaticofacial or zygomaticotemporal (maxillary division of the trigeminal nerve that provides sensation to the lateral face), and the parasympathetic fibers to the lacrimal gland can be damaged.

Limited lateral orbitotomy The lateral orbitotomy approach by Harvey is the least difficult procedure, and provides reasonably good exposure of the lateral orbit. After draping, the skin incision by scalpel blade extends from the middle of the lower eyelid to the caudal aspects of the zygomatic arch (Fig. 4.21a,b). The underlying subcutaneous tissues are carefully dissected to permit transection of the orbicularis oculi, retractor anguli oculi, and lateral orbital ligament attachment to the dorsal border of the zygomatic arch. With careful dissection the lateral orbital ligament is reflected dorsally to reveal the lacrimal gland (arrow, Fig. 4.21c) which is immediately beneath the lateral orbital ligament. Blunt deeper dissection, both caudally and rostrally on the dorsal aspects of the zygomatic arch, permits observation of the dorsal portion of the zygomatic gland and lateral periorbital fascia (Fig. 4.21d). The zygomatic salivary gland in the dog occupies the ventrorostral position of the orbital floor. For additional exploration of the orbit, a central portion of the zygomatic arch is removed (Fig. 4.21e–h). A dorsal section of zygomatic arch periosteum is reflected by periosteal elevator, and a 1–2 cm section of the arch is removed in small pieces by rongeur. Immediately medial to the zygomatic arch is the zygomatic salivary gland. With additional dissection, most of the zygomatic salivary gland can be localized (Fig. 4.21i). When the zygomatic arch is partially removed, additional areas within the ventral orbit become accessible. By digital exploration the orbital floor can evaluated, including the infraorbital artery and accompanying maxillary or

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Fig. 4.21 Lateral (limited) orbitotomy (Harvey approach): This procedure provides limited access to the lateral orbit; when combined with partial to total resection of the middle portion of the zygomatic arch, access to the entire lateral orbital walls and most of the orbital floor is possible. This procedure (or minor variations thereof) is the most frequent orbitotomy performed in the dog. (a) The skin incision extends 1 cm lateral from the medial canthus, along the dorsal edge of the zygomatic arch, and terminates about 2 cm caudal of the zygomatic crest. (b) Intraoperative appearance showing the skin incision. The exact position and its length vary depending on the target position (dorsal or ventral) within the orbit. (c) With careful dissection of the subcutaneous tissues, the retractor anguli and orbicularis oculi muscles are transected from their attachments to the lateral orbital ligament to reveal the lacrimal gland (arrow). (d) After transection of the ventral attachment of the lateral orbital ligament to the zygomatic arch, the lateral orbital ligament is reflected dorsally to expose the lateral aspects of the orbital tissues including the zygomatic (orbital) salivary gland (arrow). (e) For exploration of the canine ventral orbit, a central portion of the zygomatic arch is isolated. To maximize entry into the retrobulbar space, the zygomatic arch is removed temporarily by transecting its two ends. It is reattached by four wire sutures during wound closure. (f) A variably sized section of the zygomatic arch periosteum is elevated and portions of the bone are removed by rongeur or bone saw, exposing the majority of the zygomatic salivary gland. (g) Digital exploration of most of the rostral orbital floor is possible. Orbital fat can be excised to facilitate exploration. (A) Lacrimal gland; (B) globe; (C) zygomatic salivary gland; (D) retrobulbar fat. (h) Limited exploration of the medial retrobulbar area is possible by instrumentation (usually a small curved hemostat). (i) Intraoperative appearance in a patient with an orbital mucocele. The cyst wall is being retracted during its excision from within the orbit. After cyst removal, the entire zygomatic gland is also excised. (An alternative to surgery is to inject the mucocele with sclerosing agents, such as tetracycline or polidocanol.) (j) Closure consists of reapposition of the zygomatic arch periosteum, reattachment of the ventral portion of the lateral orbital ligament to the zygomatic arch, and closure of the subcutaneous and skin layers. (k) Immediate postoperative appearance after orbitotomy in the patient from Figure 4.21i. (All drawings with permission from Bistner SI, Aguirre G, Batik, G 1977 Atlas of Veterinary Ophthalmic Surgery. WB Saunders, Philadelphia.)

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infraorbital nerve, pterygopalatine ganglion, and palatine nerves. By digital or blunt instrument probing, the extraocular muscle cone can be evaluated dorsally and ventrally. Removal of some orbital adipose tissues can aid in visualization of the retrobulbar area. A linear incision along the long axis of the retrobulbar muscle cone permits inspection of these tissues, including the orbital portion of the optic nerve. Closure of the lateral orbitotomy apposes the tissues in reverse order (Fig. 4.21j). If excision of tissue or an infected area creates a sizeable defect, a soft rubber or silicone Penrose-type tube is positioned to exit through the masseter muscle ventral to the zygomatic arch. The orbital tissues are usually apposed with a few 2-0 to 4-0 simple interrupted absorbable sutures, as is the periosteum of the zygomatic arch, and the lateral orbital ligament is reattached to the zygomatic arch periosteum with similar type sutures. The zygomatic arch bone will regenerate within the periosteal space. If a single portion of the zygomatic arch was removed, it can be repositioned and wired to the adjacent edges of the arch. If necessary, simple interrupted absorbable sutures are indicated to minimize any dead space. The subcutaneous tissues are apposed with 2-0 to 4-0 simple interrupted absorbable sutures; the skin incision is apposed with 3-0 to 4-0 simple interrupted non-absorbable sutures. As the blink reflex is usually impaired postoperatively, a complete temporary tarsorrhaphy is performed to prevent exposure keratitis. After the blink reflex can be elicited postoperatively, the temporary tarsorrhaphy sutures can be removed (Fig. 4.21k).

medial aspect of the zygomatic arch are separated by blunt dissection with a periosteal elevator. The zygomatic arch, along with the lateral orbital ligament, is reflected dorsally and rostrally from the wound. With the zygomatic arch removed from the surgical site, inspection of the dorsolateral orbit from its rostral border to just in front of the caudal bony orbital wall is possible (Fig. 4.22f). Careful blunt medial dissection of the ventral endorbita reveals the maxillary artery, the maxillary branch of the maxillary nerve, pterygoid muscles, and the pterygopalatine ganglion and nerve. The endorbita of the extraocular muscle cone can be incised carefully along the long axis of the optic nerve. Blunt dissection reveals the optic nerve, ciliary ganglion, retractor bulbi muscles, and the posterior aspects of the globe. Closure of the surgical wound begins with replacement of the zygomatic arch with 18 g stainless steel wire sutures through the eight previously drilled holes and reattachment of the masseter muscle to the ventral zygomatic arch. The edges of the temporalis muscle are reapposed to their original position at the external sagittal crest, external zygomatic process, and the dorsal edge of the zygomatic arch with 2-0 to 4-0 simple interrupted absorbable sutures. The subcutaneous tissues are apposed with 2-0 to 4-0 simple interrupted or simple continuous absorbable sutures. The skin is apposed with 2-0 to 4-0 simple interrupted nonabsorbable sutures (Fig. 4.22g). A rubber or silicone Penrosetype drain, positioned in the retrobulbar space and directed beneath the zygomatic arch for surgical drainage, is indicated for a few days postoperatively. A complete temporary tarsorrhaphy finalizes the procedure.

Major lateral orbitotomy This modified lateral and more versatile orbitotomy provides both lateral and dorsal exposure of the posterior orbit (extraconal space), the intraconal space (with the lateral rectus muscle insertions incised), and for those infrequent patients that appear to have both lateral and dorsal retrobulbar (such as zygomatic gland cysts and neoplasms) or intraconal orbital masses. After surgical preparation and draping, the initial skin incision is made by scalpel blade, starting at the posterior aspect of the zygomatic arch and continuing along the dorsal zygomatic arch to the posterior aspects of the lateral orbital ligament (Fig. 4.22a). The skin incision is then continued dorsally following the posterior curve of the zygomatic process of the frontal bone to terminate in the middle of the external sagittal crest (Fig. 4.22b,c). The palpebral nerve lies subcutaneous and dorsal to the zygomatic arch and should not be disturbed. The skin flap is dissected free of its subcutaneous attachments and reflected caudally. The rostral aponeurosis of the temporalis muscle is incised about 4 mm from its rostral and medial edges to permit convenient reapposition. The temporalis muscle is reflected sufficiently caudally to expose the dorsal retrobulbar space (Fig. 4.22d,e), either by separating its attachment to the periosteum of the parietal bone or by a periosteal elevator to remove both the periosteum and temporalis muscle attachment together. After some superficial dissection, the zygomatic arch is isolated and four holes are drilled at each end prior to its resection. These holes will be used to reattach the zygomatic arch during closure. Both ends of the zygomatic arch are incised, and the temporalis and masseter muscles on the

Dorsal orbitotomy This extensive orbitotomy, reported by Slatter and Abdelbaki in the dog, yields reasonable exposure of the dorsomedial orbital wall, anterior frontal bone and zygomatic process, and the dorsal retrobulbar tissues, and is less often performed. This surgical approach can also damage some portions of the palpebral nerve, particularly the branches to the upper eyelid. In this procedure the temporalis muscle attachments to the frontal bone are reflected dorsally and posteriorly to provide access to the dorsal orbit and retrobulbar area. After draping, a curved skin incision is made, starting external to the sagittal crest and continuing along the posterior margin of the lateral orbital ligament. This skin flap is reflected laterally and ventrally. The periosteum of the frontal bone next to the sagittal crest is incised by scalpel and the temporal muscle reflected caudally with a periosteal elevator, and laterally to the lateral orbital ligament. With this flap of temporal muscle reflected laterally, the dorsal orbit and retrobulbar muscles can be visualized. Closure starts with reapposition of the periosteum along the external sagittal crest, and routine closure of the subcutaneous and skin layers.

Anterior orbitotomies The anterior orbitotomy procedure may be used for lesions in the anterior orbit that are cranial to the equator of the globe. Indications for this approach include zygomatic gland cysts and masses, nictitating membrane cysts and tumors, extraocular muscle biopsies, some retinal detachment surgeries, and disorders of the lacrimal gland.

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G Fig. 4.22 The lateral orbitotomy reported by Slatter and Abdelbaki provides for more extensive exposure of the dorsal canine orbit. (a) The initial skin incision extends the entire length of the zygomatic arch. (b) The skin incision is continued dorsal and immediately lateral of the frontal crest: (A) skin flap; (B) lateral orbital ligament; (C) zygomatic arch; (D) frontal crest. (c) Operative appearance of the lateral orbitotomy skin incision. (d) To reflect the temporalis muscle (arrow) caudally, its aponeurosis is incised along the external frontal and sagittal crests, and the dorsal aspects of the zygomatic arch. A major section of the zygomatic arch is transected and eight holes are pre-placed to facilitate its reattachment. (e) Operative appearance of the U-shaped incision of the aponeurosis of the temporalis muscle prior to its elevation and reflection caudally. The zygomatic arch is immediately below the lower temporalis muscle incision. (f) With removal of the central zygomatic arch and caudal reflection of the temporalis muscle from its medial and lateral attachments, a major portion of the posterior orbit can be directly explored. (A) Frontalis muscle; (B) temporalis muscle; (C) lateral rectus muscle; (D) ventral oblique muscle; (E) ventral rectus muscle; (F) optic nerve; (G) resected zygomatic arch and lateral orbital ligament. (g) Immediate postoperative appearance after lateral orbitotomy for the excision of a zygomatic salivary mucocele. Following this procedure, the patient’s blink reflex may be impaired and a temporary tarsorrhaphy is used for 7–10 days to protect the cornea. The tarsorrhaphy sutures are not removed until a ‘brisk’ blink reflex returns. (All drawings with permission from Slatter DH, Abdelbaki Y 1979 Lateral orbitotomy by zygomatic arch resection in the dog. Journal of the American Veterinary Medical Association 175:1179–1183.)

Access to the anterior orbit may be through either the bulbar conjunctiva (transconjunctival) or the eyelids (transpalpebral). These two approaches provide limited exposure to the retrobulbar (intraconal) space and tissues. Often the dorsal or dorsolateral anterior orbit is entered via the transconjunctival approach which avoids damage to the palpebral nerve branches. Entry into the dorsal orbit may be through either limbal or fornix-based conjunctival incisions. The transpalpebral approach is used for lesions in the ventral anterior orbit. The approach is through the lower eyelid and under the ventral conjunctival fornix. Both of these

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approaches are indicated for orbital biopsies, and to excise conjunctival neoplasms that extend caudally into the anterior orbit. The surgical approach through the conjunctiva has a greater chance of sepsis as this area cannot be sterilized preoperatively. With both anterior approaches, the lid and conjunctival incisions are parallel to the orbital rim. The dissection is continued deeper by blunt tenotomy or strabismus scissors. Once the mass is ‘shelled out’, closure is usually by two layers for the transconjunctival approach, apposing the subconjunctiva, endorbita, and conjunctiva with 4-0 simple

Orbitotomy in large animals and special species

interrupted absorbable sutures. For the transpalpebral approach, the endorbita and tarsus are apposed with 4-0 simple interrupted absorbable sutures and the skin with 2-0 to 40 simple interrupted non-absorbable sutures. Sometimes to facilitate orbital exposure, insertions of the rectus muscles are incised, and reattached later with 6-0 absorbable mattress sutures.

Transoral orbitotomy The transoral approach to the caudal orbit is immediately behind the last molar teeth in the dog and cat, and used for fine-needle aspiration of orbital masses, and ventral drainage of orbital cellulitis and abscessation. In the dog, this portion of the orbital floor is composed primarily of the medial pterygoid muscle and periorbital fascia, and the oral submucosa and mucosa (Fig. 4.23). In the cat, the caudal orbital floor is quite thin, consisting of only a small shelf of tuberous maxillary bone and soft tissues. The oral approach, because of its very limited exposure, is used primarily for culture and cytology of the retrobulbar space, and to provide ventral drainage for orbital cellulitis. Because the mouth is a septic environment, entry into the orbit generally requires the perioperative administration of systemic antibiotics. After short-acting general anesthesia, the animal is intubated and a mouth speculum positioned. Povidone–iodine (0.5% solution) is applied to the oral mucosa immediately caudal to the last molar tooth. After a 5–10 mm linear incision, a blunt probe is inserted into the retrobulbar space. Bacterial and fungal cultures and cytology specimens can be collected. The incision is not closed, but allowed to heal by secondary intention.

Total and partial orbitectomy The partial and total orbitectomy procedures are used to treat orbital and periorbital neoplasia, and include removal of the eye, the other orbital tissues, and not infrequently adjacent bony, sinus, nasal, and oral structures. Muscles adjacent to the orbit, such as the temporalis and masseter, and bones, such as portions of the frontal, zygomatic arch,

Fig. 4.23 Oral orbitotomy: Immediately posterior to the last molar tooth (arrow) is the area to enter the orbit from the mouth. This entry site is most useful for orbital culture and cytology, and to provide ventral drainage for septic orbital cellulitis.

maxilla, and others, may be excised. With total orbitectomies, the globe is removed. Although these more radical surgical approaches are definitely more aggressive, there was local recurrence of orbital neoplasia in 37% of the patients. However, 50% of the patients remained tumor free for 12 months postoperatively.

Orbitotomy in large animals and special species An orbitotomy is indicated in the horse for excision or biopsy of orbital or retrobulbar masses, removal of orbital foreign bodies, and drainage of retrobulbar abscesses that are not responsive to systemic therapy. An orbitotomy may be needed to repair orbital fractures in the horse. Orbitotomies are rarely performed in horses due to the complex nature of the anatomy of the equine orbit and the infrequent indications for the procedure. The most frequent indication is to provide exposure to repair orbital fractures. Due to the infrequent use of the procedure, the surgeon should prepare a careful surgical plan preoperatively, review the anatomy of the area, and peruse the surgical literature to plan the surgical episode. Orbitotomy is a challenging procedure and requires advance planning. An equine skull for review and for visualization of threedimensional concepts during surgery is helpful. An equine anatomic atlas is also helpful. A general equine surgical instrument pack and orthopedic instruments are necessary. An oscillating bone saw, orthopedic drill, periosteal elevators, wire ‘tighteners’, and rongeurs are needed. Two orbital surgical procedures have been described for orbital exploration in the horse: 1) a dorsal orbitotomy approach (Basher et al); and 2) osteotomy of the zygomatic, temporal, and frontal bone components of the zygomatic arch (Koch, Goodhead, and Colitz). The dorsal orbitotomy technique is initiated by careful attention to skin preparation for aseptic surgery. A generous, slightly curved skin incision is made over the dorsal orbit, lateral to the external sagittal crest of the frontal and parietal bones, extending posterior to the zygomatic process of the frontal bone. Lateral retraction of the attachments of the frontoscutularis, interscutularis, and temporal muscles to the temporal and frontal bones allows exposure of the extraocular muscle cone. The second technique involves resection of the zygomatic, temporal, and frontal bone components of the zygomatic arch. A large lateral canthotomy is performed to maximize exposure. A curved skin incision is made over the zygomatic process of the frontal bone, care being taken to preserve the sensory nerve fibers from the frontal nerve and the motor fibers to the orbicularis oculi muscle laterally from the palpebral branch of the facial nerve. The periosteum of the cranial rim of the zygomatic process is incised along its length, and the aponeuroses of the frontoscutularis, interscutularis, temporal, and masseter muscles are reflected. Next, 1.5–2 mm holes are predrilled in the zygomatic process of the frontal bone, the zygomatic arch, and the zygomatic process of the temporal bone. Three bone cuts are then made with an oscillating bone saw. The first is through the zygomatic process of the frontal bone, the next through the zygomatic arch, and the last through the zygomatic

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process of the temporal bone. The resulting wedge of bone is removed to expose the dorsolateral orbit, retrobulbar muscle cone, and the orbital lacrimal gland. The bone wedge is placed in a bowl of sterile saline until needed to replace the bony defect. The orbital lesion is addressed by excision, biopsy, or aspiration. Iridium seeds may be implanted or cisplatin injected into a cancerous mass. The procedure is completed by replacing the bone wedge and using 18–22 g stainless steel wire to reattach the bone through the predrilled holes. The periosteum is reattached using 3-0 polyglycolic acid sutures in a simple interrupted pattern. The subcutaneous tissues are closed with 3-0 to 4-0 absorbable sutures. Skin and lateral canthotomy incisions are sutured with 3-0 to 4-0 nylon or prolene sutures.

possible, using walking sutures and vertical mattress sutures, and the remaining defect is allowed to heal as a granulating open wound or by second intention. Early in the healing process the area should be disinfected, kept clean, and bandaged. Parenteral antibiotics are administered until a good granulation bed is present in the orbit. The orbit is flushed with sterile saline until a healthy granulation tissue bed covers the orbit; lavage is then continued with water. Owners should be prepared for a long-term management period, but a good result can be expected in most cases. Reconstructive skin flaps and grafts should also be considered. Consultation with an equine surgeon is of benefit to determine the best therapeutic modality for each case.

Orbital fracture repair An orbital rim fracture is a potential globe- and visionthreatening injury. These fractures may result in bone fragment displacement, impingement of extraocular muscles, laceration of the globe, impairment of the blink reflex, and restriction of ocular movement. The dorsal orbital rim is fractured most frequently. Diagnosis may be made by examination and palpation, by orbital radiographs, and by CT. The zygomatic arch of the frontal bone may be fractured in one piece. Reduction is usually facilitated by intravenous non-steroidal anti-inflammatory agents and warm compresses for 12–24 h. The fracture may be reduced and repositioned without a surgical incision and without fixation devices. Bone chips in comminuted orbital fractures that are too small to be fixed in position are preferably removed to prevent bone sequestration and osteomyelitis. Ventral orbital rim fractures also occur from various injuries. Polo horses may be more prone to ventral orbital rim fractures. Traumatic fractures of the medial orbit may affect the nasolacrimal canaliculus or nasolacrimal duct. Horses that fall over backward may have fractures of the basioccipital bone and basisphenoid bone of the inner orbit resulting in blindness. CT will delineate these fractures clearly, whereas orbital radiographs do not allow optimal visualization.

Surgical management of traumatic proptosis in small animals Although the surgical management of traumatic proptosis involves primarily eyelid and lateral canthal surgery, proptosis is an important acute orbital disease. The prognosis for traumatic proptosis is determined by several factors. The breed of the dog should be considered as traumatic proptosis occurs more frequently in brachycephalic breeds with shallow orbits and large palpebral fissures. The trauma to produce proptosis in brachycephalic breeds is less than in mesocephalic and dolichocephalic breeds. Traumatic proptosis in cats is infrequent, and is associated with considerable trauma; skull and/or mandibular fractures are often concurrent (Fig. 4.24). The duration of the proptosis must be considered: the longer the cornea is exposed, the more extensive the damage to the epithelium and stroma, and the more extensive the retrobulbar hemorrhage and edema. The size of the resting pupil and the light-induced pupillary reflexes can help to assess possible damage to the optic nerve and pupillary pathways. A widely dilated pupil, with

Partial orbital rim resection for large eyelid skin defects/cosmetic skin orbitectomy When large eyelid skin resection is needed to remove neoplastic masses following enucleation or exenteration, an orbital rim resection will assist closure of the skin margins. In this procedure, the globe is removed, and the neoplastic mass is excised with a large margin. If the skin margins are too far apart to be apposed, an osteotome or oscillating bone saw is used to remove a large amount of the dorsal and lateral rim of the zygomatic process, allowing sufficient movement of the skin to achieve more close apposition of the skin edges. Walking sutures may be used to assist in skin movement to cover the defect. A cross mattress suture pattern may be used, with gradual tightening of the sutures to close the defect. Releasing incisions are also beneficial in allowing adequate skin to cover the defect completely. In severe cases, when sufficient skin cannot be mobilized even with zygomatic arch resection, the orbit may remain open and heal. In these cases the skin is closed as much as

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Fig. 4.24 Proptosis in the cat usually requires a more guarded prognosis than in the dog, because the trauma to displace the globe from the orbit is more extensive, and the resultant damage to the eye and orbit is considerable.

Surgical augmentation of orbital volume in small animals

limited or no light-induced pupillary reflex, signals neural damage. Traumatic proptosis is rare in the other species, and in the horse often incomplete, presenting as acute exophthalmia (secondary to intraorbital hemorrhage), impaired and incomplete blink reflex, and progressive corneal ulceration. Careful orbital examination may detect orbital bone fractures with variable displacement. The prognosis for vision must be cautious, as blindness occurs in about 60% of dogs and 100% of cats. Postproptosis strabismus in dogs is frequent, occurring in 36% of the dogs. The medial rectus muscles are most frequently avulsed; the ventral rectus and ventral oblique muscles are less often involved. Traumatic proptosis is one of the few ophthalmic emergencies in all species (Fig. 4.25). As soon as possible, topical solutions should be applied frequently to the exposed cornea to minimize damage. After total patient evaluation and short-acting general anesthesia, the eyelids are prepared quickly for aseptic surgery. After draping, a liberal (10–15 mm) lateral canthotomy is performed with Steven’s tenotomy or strabismus scissors. A lateral canthotomy is Fig. 4.26 Replacement of the globe during lateral canthotomy and complete temporary tarsorrhaphy. As in this patient, hemorrhage within the orbit causes the globe to place considerable pressure on the temporary tarsorrhaphy. Small clear plastic or rubber band stents are placed under the interrupted mattress sutures to maintain the complete temporary tarsorrhaphy for 10–14 days.

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usually necessary to increase the size of the palpebral fissure in order to return the globe to the orbit. To temporarily cover the cornea and provide direct pressure to the globe, so as to decrease orbital hemorrhage and orbital edema, a complete temporary tarsorrhaphy is performed (Fig. 4.26). Four to six 2-0 to 4-0 non-absorbable interrupted horizontal sutures with stents are pre-placed. Stents may consist of old intravenous tubing, buttons, wide rubber bands or silicone strips. Stents are indicated because of eyelid edema and the considerable pressure that occurs on these sutures. Once all of the eyelid sutures are placed, they are tightened and tied with long ends to accommodate either intermittent ophthalmic examinations or to permit adjustments as the eyelid and orbital swelling decreases. The postoperative medical management of traumatic proptosis will be summarized in the subsequent section.

Surgical augmentation of orbital volume in small animals

B Fig. 4.25 Traumatic proptosis in a small mixed-breed dog. (a) The globe is displaced beyond the eyelid margins and subconjunctival hemorrhage is evident. (b) Appearance of the globe after replacement and the sutures are tied.

Enucleation and exenteration surgeries, trauma, and inflammation can significantly reduce orbital volume, such that health and function of the eye may be impaired. When significant amounts of orbital tissue (including the eye) have been lost, surgical implants such as the silicone and methyl methacrylate spheres (flattened on one side) may be positioned and anchored within the orbit. Non-absorbable sutures (nylon or mylar) and surgical mesh may be used to bridge the bone orbital opening before a permanent tarsorrhaphy is performed to reduce the postoperative concavity that follows.

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POSTOPERATIVE CARE AND MANAGEMENT Perioperative antibiotics are indicated in most orbital surgical procedures. Surgical entry into the orbit through the conjunctiva or mouth should always be considered as possibly contaminated, as these surfaces cannot be sterilized. Surgical drains are infrequently placed in small animals except after lateral and dorsal orbitotomies. Topical antibiotics are instilled perioperatively for eviscerations, and after the more difficult orbitotomies. Systemic corticosteroids and NSAIDs are often administered systemically after traumatic proptosis and eviscerations to reduce orbital inflammation and swelling. Diuretics may also assist in the reduction of excessive orbital fluids. Warm and cold compresses can reduce postoperative eyelid and orbital swelling after all of these surgical procedures. Use of the E-collar postoperatively is good preventive therapy against self-trauma. For those patients with considerable orbital swelling and a visual eye, a complete temporary tarsorrhaphy is often indicated to protect the cornea. Postoperative exophthalmia may increase and impair the blink reflex. Partial-to-complete loss of the blink reflex produces a central corneal ulceration that often progress rather rapidly. The tarsorrhaphy should remain until a vigorous blink reflex returns, which may be several weeks. Hence, single sutures from the tarsorrhaphy may be removed over several days to weeks, to maintain corneal health.

Postoperative complications and treatment in all species Enucleation The complications after enucleation are not usually serious. Swelling immediately after surgery is usually associated with orbital hemorrhage; it may be more frequent after the transpalpebral technique than the subconjunctival method. Orbital hemorrhage may be associated with poor hemostasis during surgery, or from blood vessels that did not bleed and were not ligated during surgery because of the low blood pressure. Counterpressure with a temporary facial bandage is a possibility. Ice packs for a few hours postoperatively may reduce the swelling. Some hemorrhage may also be apparent between the sutures in the skin incision. Orbital hemorrhage may also exit the nose and is thought to be related to the passage of orbital blood through the nasolacrimal system. Postoperative infections after enucleation are infrequent in small animals because of the perioperative administration of systemic antibiotics. Infections usually occur within the first week postoperatively. Culture of the orbital contents is recommended for the selection of the most appropriate antibiotic(s) after oral orbitotomy for orbital cellulitis or for postoperative orbital infections. High levels of systemic antibiotics are recommended for 7–10 days. Postoperative orbital infections with an orbital prosthesis usually require removal of the implant to resolve the orbital infection. Intraorbital prostheses may be less successful in cats than in dogs; about 20–40% of the implants extrude in cats. The reasons are not understood, and although fluid

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Fig. 4.27 Postoperative appearance of a young Great Dane 5 weeks after enucleation. With the short-hair coat breeds, postoperative disfigurement and concavity of the orbit occurs.

accumulation around the implant is a common finding in cats, septic infections are not usually present. The most frequent long-term complication after enucleation is the contracture of the orbital space and the concavity of the permanent complete tarsorrhaphy. This sinkage may be quite noticeable in short-haired dogs and cats, but less obvious in long-haired breeds (Fig. 4.27). Implantation of an orbital sphere after enucleation will markedly reduce the postoperative orbital and eyelid deformity to acceptable levels. Swelling of the orbit or space between the conjunctival sacs may develop infrequently weeks to months postoperatively. Retained lacrimal and/or nictitating membrane glandular tissues are the most likely sources if the swelling is liquid. If the swelling becomes troublesome, excision of the respective glands will generally resolve the problem. Orbital emphysema occurs infrequently postoperatively, and appears to be caused by the passage of air from the nose, through the nasolacrimal duct, into an anterior orbital space. Sneezing by the animals can initiate rather acute and marked swelling of the complete permanent tarsorrhaphy. Resolution consists of excision of one or both of the patent lacrimal puncta. Occasionally a small but chronic fistula from retained conjunctiva may develop, resulting in small amounts of brown fluid that stain the eyelids. Treatment consists of freshening the fistula’s edges and apposition by sutures. Occasionally the lacrimal and/or nictitating membrane gland may also need to be excised.

Evisceration The evisceration procedure is nearly always accompanied with an intraocular prosthesis (Fig. 4.28). The surgical success rate of eviscerations in dogs is 90–95%, but is not reported in cats and horses. Postoperative infections are infrequent, but can necessitate prosthesis removal and even enucleation. Perioperative antibiotics seem to prevent most

Postoperative complications and treatment in all species

A

B

Fig. 4.28 (a) Postoperative appearance of bilateral evisceration with an intrascleral silicone prosthesis 12 months after surgery in a 10-year-old Beagle. The presurgical condition was absolute primary glaucoma which was intractable to continued topical medications. (b) Close-up of the right eye. Usually some corneal edema and/or pigmentation occur after this procedure. Topical medications after 2–4 weeks postoperatively are usually not necessary.

postoperative infections. Long-term successful eviscerations require an intact and reasonably healthy cornea. Postoperative corneal diseases, possibly related to the intraocular implant, include corneal erosions and ulcerations (Fig. 4.29). Often the cornea is compromised preoperatively, as in glaucoma. During evisceration surgery, instrument contact with the posterior cornea is avoided, and in spite of the often considerable hemorrhage that accompanies the procedure, excessive flushing of the globe should be avoided. These corneas usually demonstrate edema postoperatively, but often some clearing will occur in 4–8 weeks. Some corneal superficial pigmentation and vascularization may remain permanently, but are not usually objectionable. Other extraocular diseases, such as keratoconjunctivitis sicca, may affect the cornea and indirectly the intraocular prosthesis success rate. Surgical wound dehiscence is minimized when the scleral

rather than the limbal incision is used. With the extensive incision (often 180 ) necessary to insert the near-globe size prosthesis, considerable corneal or scleral nerves may be transected, rendering these postoperative corneas subject to lower sensitivities, less frequent blinking, and increased exposure. Several weeks may be necessary for these corneal nerves to regenerate. In the event that a central corneal ulcer develops after the evisceration procedure, aggressive medical therapy (antibiotics and serum topically) and often a bulbar conjunctival graft is indicated. If the corneal ulcer becomes full thickness, a conjunctival graft is essential. Infection from the corneal ulcer into the globe with the prosthesis generally requires enucleation.

Exenteration The complications after exenteration are similar to those associated with enucleation. The postoperative swelling and the long-term wound contracture are usually greater because of the larger amounts of orbital tissues that have been excised.

Orbitotomy

Fig. 4.29 After evisceration, the most frequent complication with an intrascleral prosthesis is a central corneal ulcer which develops immediately postoperatively. This is usually very slow healing and typically requires a bulbar pedicle conjunctival graft to resolve quickly. Corneal ulceration after the evisceration procedure is best prevented by a temporary tarsorrhaphy for 10–14 days or until normal blink reflex returns.

The immediate postoperative complications after orbitotomies are usually related to exophthalmia secondary to retrobulbar swelling and hemorrhage, especially after the lateral approaches. The lateral orbitotomies usually transect at least some of the palpebral nerve branches that supply the upper eyelid. As a result, a temporary complete tarsorrhaphy is recommended after all orbitotomies until eyelid swelling is reduced, and a reasonable blink response returns (which may be several weeks). Without a blink reflex, neuroparalytic keratitis and corneal ulceration can develop rapidly. If the lacrimal gland innervation is impaired, tear production may also be insufficient. Oral pilocarpine (usual dose for a 15 kg dog is 2 drops of 2% ophthalmic pilocarpine well mixed in the food, twice daily) will successfully stimulate the denervated gland.

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Post-proptosis Complications after the surgical treatment of traumatic proptosis include short-term retrobulbar hemorrhage and swelling, and corneal malacia and ulceration with secondary iridocyclitis. Systemic corticosteroids, NSAIDs, and diuretics can be administered to rapidly reduce the retrobulbar fluids, and reduce the pressure on the globe and intraorbital portion of the optic nerve. Treatment of corneal disease, hyphema, and anterior uveitis usually consists of topical antibiotics and mydriatics administered between the complete temporary tarsorrhaphy sutures or by the subpalpebral system. Long-term sequelae of traumatic proptosis include enophthalmia and limited globe mobility (related to the loss of orbital fat and orbital fibrosis), optic nerve atrophy (related to excessive pressure of the optic nerve and possible ischemia of the optic nerve), pigmentary keratitis, lagophthalmia, papilloedema, and exotropia (most often divergent strabismus related to palsy or transection of the medial rectus muscle; Fig. 4.30). Attempts to correct the exotropia are not always successful. If the innervation to the medial rectus muscle has been impaired, spontaneous partial-to-complete recovery may occur in several months. If the exotropia is secondary to tearing of the medial rectus muscle or its insertion, spontaneous recovery is unlikely. Treatment usually consists of reapposition of the torn medial rectus portions, or splitting the dorsal rectus muscle and reattaching it medially as previously described.

Short- and long-term results in all species Enucleation The short- and long-term results after enucleation are good. The majority of complications can be either medically or surgically managed. The deformity associated with the loss of the eye is greatly reduced by the use of orbital prostheses.

Fig. 4.30 One of the more frequent complications after traumatic proptosis in the dog is lateral strabismus, which results from either rupture of the medial rectus muscle (the shortest of the retrobulbar muscles) or its insertion just posterior to the globe. Damage to this muscle and/or its nerve supply causes lateral strabismus. A shallow ventral corneal ulcer is also present; it resulted from exposure and an inadequate blink reflex.

86

Although the patient numbers are still limited, intraorbital prostheses may be less successful in cats.

Evisceration The evisceration procedure with intraocular prosthesis has largely replaced the enucleation procedure for the treatment of end-stage, blind, painful and enlarged glaucomatous eyes. The postoperative results are a corneoscleral shell with an intrascleral sphere that is cosmetically acceptable, painless, and has normal ocular movements with the fellow eye. Use of the evisceration procedure with intrascleral prostheses for globes with non-specific uveal inflammations and suspected intraocular neoplasms is not recommended. As a quality control, the intraocular tissues after evisceration should always be examined histologically. The success rate in dogs after evisceration with intrascleral prosthesis is 90–95%, with corneal ulceration as the most frequent complication. As corneal ulcerations tend to heal very slowly in postoperative evisceration eyes with intraocular prostheses, early treatment with bulbar conjunctival grafts is recommended.

Exenteration The short- and long-term success after exenteration is less than with enucleation and evisceration, because this procedure is used primarily for the attempted excision of primary orbital neoplasms. In the event that total excision of the primary orbital neoplasm is achieved, the main evidence of exenteration is the complete permanent tarsorrhaphy, and sinkage of the eyelids and orbit associated with the loss of all of the orbital tissues. Use of a silicone or methyl methacrylate sphere within the orbit after exenteration can markedly reduce, but not totally eliminate, the postoperative sinkage.

Orbitotomy The judicious choice of a specific orbitotomy procedure for orbital disease will minimize the possible short- and longterm side effects. Orbitotomy procedures provide excellent results when used for orbital cysts, benign tumors, and focal inflammations. Orbitotomies for orbital neoplasia are less successful, because the incomplete excision of these malignant tumors is often unavoidable. Based on current information available on canine primary orbital neoplasms, exenteration or the orbitectomy procedure may be the preferred surgical procedure. The orbitectomy procedure may have more success with complete excision of malignant orbital neoplasms than the lateral orbitotomy methods, but results in more postoperative disfigurement. A common sequela to surgery, some periorbital fibrosis usually develops, resulting in some enophthalmia and restricted globe mobility. The loss of orbital adipose tissue may also result in enophthalmia. Some long-term ptosis or drooping of the upper eyelid may persist, probably related to partial loss of some branches of the palpebral nerve.

Traumatic proptosis Postoperative complications related to the surgical treatment of traumatic proptosis are primarily associated with the

Further reading

disease. The improper placement of the eyelid sutures can produce direct corneal damage. These sutures must only partially penetrate the eyelid thickness, and emerge through the

middle of the eyelid margin. As the eyelid swelling decreases, these sutures may require multiple readjustments to avoid corneal contact.

Further reading Small animals Bartoe JT, Brightman AH, Davidson HJ: Modified lateral orbitotomy for visionsparing excision of a zygomatic mucocele in a dog, Vet Ophthalmol 10:127–131, 2007. Bedford PGC: Orbital pneumatosis as an unusual complication to enucleation, J Small Anim Pract 20:551–555, 1979. Bellhorn RW: Enucleation technique: a lateral approach, J Am Anim Hosp Assoc 8:59–60, 1972. Blocker T, Hoffman A, Schaeffer DJ, Wallin JA: Corneal sensitivity and aqueous tear production in dogs undergoing evisceration with intraocular prosthesis placement, Vet Ophthalmol 10:147–154, 2007. Brightman AH, Magrane WG, Huff RW, Helper LC: Intraocular prosthesis in the dog, J Am Anim Hosp Assoc 13:481–485, 1977. Gilger BC, McLaughlin SA, Whitley RD, Wright JC: Orbital neoplasms in cats: 21 cases, J Am Vet Med Assoc 201: 1083–1086, 1992. Gilger BC, Whitley RD, McLaughlin SA: Modified lateral orbitotomy for removal of orbital neoplasms in two dogs, Vet Surg 24:53–58, 1994. Gross S, Aguirre GD, Harvey C: Tumors involving the orbit of the dog, Proceedings of the American College of Veterinary Ophthalmologists 8:229–240, 1979. Hamor RE, Roberts SM, Severin GA: Use of orbital implants after enucleation in dogs, horses, and cats: 161 cases (1980–1990), J Am Vet Med Assoc 203:701–706, 1993. Hamor RE, Whitley RD, McLauglin SA, Lindley DM, Albert RA: Intraocular silicone prostheses in dogs: a review of the literature and 50 new cases, J Am Anim Hosp Assoc 30:66–69, 1994. Harvey CE: Exploration of the orbit. In Bistner SI, Aguirre G, Batik G editors: Atlas of Veterinary Ophthalmic Surgery, Philadelphia, 1977, WB Saunders, pp 258–260. Hendrix DVH, Gelatt KN: Diagnosis, treatment and outcome of orbital neoplasia in dogs: a retrospective study of 44 cases, J Small Anim Pract 41:105–108, 2000. Hong YJ, Jang SU, Lee JH: Limited orbitotomy without transection of the orbital ligament for zygomatic mucocele in three brachycephalic dogs. In Proceedings of the 38th Meeting of the American College of Veterinary Ophthalmologists: Abstract 4, 2007. Kennedy RE: The effect of early enucleation on the orbit in animals and humans, Am J Ophthalmol 60:277–306, 1965. Kern TJ: Orbital neoplasia in 23 dogs, J Am Vet Med Assoc 186:489–491, 1985.

Kern TJ: The canine orbit. In Gelatt KN editor: Veterinary Ophthalmology, ed 2, Philadelphia, 1991, Lea and Febiger, pp 239–255. Koch SA: Intraocular prosthesis in the dog and cat: the failures, J Am Vet Med Assoc 179:883–885, 1981. Konrade KA, Clode AB, Michau TM, Roe SC, Trumpatori BJ, Krug WV, Gilger BC: Surgical correction of severe strabismus and enophthalmos secondary to zygomatic arch fracture in a dog, Vet Ophthalmol 12:119–124, 2009. Martin CL: Orbital emphysema: a complication of ocular enucleation in the dog, Vet Med 66:986–989, 1971. McLaughin SA, Ramsey DT, Lindley DM, et al: Intraocular silicone prosthesis implantation in eyes of dogs and a cat with intraocular neoplasia: nine cases (1983–1994), J Am Vet Med Assoc 207:1441–1443, 1995. Mughannam AJ, Reinke JD: Two cosmetic techniques for enucleation using a periorbital flap, J Am Anim Hosp Assoc 30:308–312, 1994. Nasisse MP, van Ee RT, Munger RJ, Davidson MG: Use of methyl methacrylate orbital prostheses in dogs and cats: 78 cases (1980–1986), J Am Vet Med Assoc 192:539–542, 1988. O’Brien MG, Withrow SJ, Straw RC, et al: Total or partial orbitectomy for the treatment of periorbital tumors in 24 dogs and 6 cats: a retrospective study, Vet Surg 25:471–479, 1996. Prince JH, Diesem CD, Eglitis I, Ruskell GL: Anatomy and Histology of the Eye and Orbit in Domestic Animals, Springfield, 1960, CC Thomas, pp 65–181 and 260–297. Ramsey DT, Fox DB: Surgery of the orbit, Vet Clin North Am Small Anim Pract 27:1215–1264, 1997. Riggs C, Whitley RD: Intraocular silicone prosthesis in a dog and a horse with corneal lacerations, J Am Vet Med Assoc 196:617–619, 1990. Simpson HD: Reconstructive surgery of the eye. I. Plastic eye prosthesis, North Am Vet 37:770–777, 1956. Slatter DH, Abdelbaki Y: Lateral orbitotomy by zygomatic arch resection in the dog, J Am Vet Med Assoc 175:1179–1183, 1979. Speakman AJ, Baines SJ, Williams JM, Kelly DF: Zygomatic salivary cyst with mucocele formation in a cat, J Small Anim Pract 38:468–470, 1997. Spiess BM: Diseases and surgery of the canine orbit. In Gelatt KN editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 539–562.

Wang AL, Ledbetter EC, Kern TJ: Orbital abscess bacterial isolates and in vitro antimicrobial susceptibility patterns in dogs and cats, Vet Ophthalmol 12:91–96, 2009. Whitley RD, Shaffer KW, Albert RA: Implantation of intraocular silicone prosthesis in dogs, The Compendium 7:802–811, 1985.

Large animals and special species Basher AW, Severin GA, Chavkin MJ, Frank AA: Orbital neuroendocrine tumors in three horses, J Am Vet Med Assoc 210:668–671, 1997. Baumel JJ, Whitmer LM: Osteologia. In Baumel JJ editor: Handbook of Avian Anatomy: Nomina Anatomica Avium, Cambridge, 1993, Nuttall Ornithological Club, pp 45–132. Beard WL, Wilkie DA: Partial orbital rim resection, mesh skin expansion, and second intention healing combined with enucleation or exenteration for extensive periocular tumors in horses, Vet Ophthalmol 5:23–28, 2002. Blogg JR, Stanley RG, Philip CJ: Skull and orbital blow-out fractures in a horse, Equine Vet J (Suppl 10): Equine Ophthalmology 5–7, 1990. Bradecamp EA, Matter NE: How to perform an enucleation in the standing horse, Proceedings of the American Association of Equine Practitioners 50:237–239, 2004. Brooks DE: Orbit. In Auer JA editor: Equine Surgery, Philadelphia, 1992, WB Saunders/ Harcourt Brace Jovanovich, pp 654–666. Brooks DE: Ocular emergencies and trauma. In Auer JA, Stick JA editors: Equine Surgery, ed 2, Philadelphia, 1999, WB Saunders, pp 508–514. Brooks DE: Orbit. In Auer JA, Stick JA editors: Equine Surgery, ed 2, Philadelphia, 1999, WB Saunders, pp 502–505. Brooks DE: Ophthalmology for the Equine Practitioner, Jackson, 2002, Teton New Media, pp 36–41. Brooks DE: Orbit. In Auer JA, Stick JA editors: Equine Surgery, ed 3, St Louis, 2006, Saunders, pp 755–766. Brooks DE, Matthews AG: Equine ophthalmology. In Gelatt KN editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 1165–1274. Caron JP, Barber SM, Bailey JV, Fretz PB, Pharr JN: Periorbital skull fractures in five horses, J Am Vet Med Assoc 188:280–284, 1986. Colitz C, Gilger BC, Davidson MG: Orbital fibroma in a horse, Vet Ophthalmol 3:213–216, 2000.

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Cutler TJ: Diseases and surgery of the globe and orbit. In Gilger BC editor: Equine Ophthalmology, St Louis, 2005, Saunders, pp 63–106. Davis JL, Gilger BC, Spaulding K, et al: Nasal adenocarcinoma with diffuse metastases involving the orbit, cerebrum, and multiple cranial nerves in a horse, J Am Vet Med Assoc 221:1460–1463, 2002. Gelatt KN, Wolf ED, Boyd CL, Titus RS: The special sense organs. In Oehme FW, Prier JE editors: A Textbook of Large Animal Surgery, ed 2, Baltimore, 1988, Williams and Wilkins, pp 623–669. Gilger BC, Davidson MG: How to prepare for ocular surgery in the standing horse, Proceedings of the American Association of Equine Practitioners 48:266–268, 2002. Gilger BC, Pizzirani S, Johnson LC, Urdiales NR: Use of a hydroxyapatite orbital implant in a cosmetic corneoscleral prosthesis after enucleation in a horse, J Am Vet Med Assoc 222:343–345, 2003. Goodhead AD, Vener IJ, Nesbit JW: Retrobulbar extra-adrenal paraganglioma in a horse and its surgical removal by orbitotomy, Veterinary and Comparative Ophthalmology 7:96–100, 1997. Grier R, Kigurardo G, Shaffer C, Pedrosa B, Myers R, Merkley DF, Touvenelle M: Mast cell destruction by deinonized water, Am J Vet Res 51:1116–1120, 1991. Hadick CL, Stoehr A, Rozmiarek H, Przybyla V: Intraocular prosthesis in a cynomolgus monkey, Vet Med Small Anim Clin 78:86–88, 1983. Hamor RE, Roberts SM, Severin GA: Use of orbital implants after enucleation in dogs, horses, and cats: 161 cases (1980–1990), J Am Vet Med Assoc 203:701–706, 1993. Hoffman D, Jennings P, Spradbrow P: Immunotherapy of bovine ocular squamous cell carcinomas with phenol–saline extracts of allogenic carcinomas, Aust Vet J 57:159–162, 1981. Irby NL: Surgical diseases of the eye in farm animals. In Fubini S, Ducharme NG editors: Farm Animal Surgery, St Louis, 2004, Saunders, pp 429–459.

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Ivany JM: Farm animal anesthesia. In Fubini S, Ducharme NG editors: Farm Animal Surgery, St Louis, 2004, Saunders, pp 97–112. Klein WER, Bier J, van Dieten JS, et al: Radical surgery of bovine ocular squamous cell carcinoma (cancer eye): complications and results, Vet Surg 13:236–242, 1984. Kleinschuster S, Rapp H, Green S, Bier J, Kampen K: Efficacy of intratumorally administered mycobacterial cell walls in the treatment of cattle with ocular carcinoma, J Natl Cancer Inst 67:1165–1171, 1981. Koch DB, Leitch M, Beach J: Orbital surgery in two horses, Vet Surg 9:61–63, 1980. Lavach JD: Large Animal Ophthalmology, St Louis, 1990, CV Mosby, pp 225–236, and 289–298. Machado M, dos Santos Schmidt EM, Montiani-Ferreira F: Interspecies variation in orbital bone structure of psittaciform birds (with emphasis on Psittacidae), Vet Ophthalmol 9:191–194, 2006. Martin CL: Ophthalmic Disease in Veterinary Medicine, London, 2005, Manson Publishing, pp 172–178. McLaughlin SA, Gilger BC, Hamilton HL, Whitley RD, Harrison IW, Comer J: Intraocular silicone prosthesis as a cosmetically acceptable alternative to enucleation in horses, Compendium of Continuing Education 17:945–951, 1995. McLelland J: Color Atlas of Avian Anatomy, Philadelphia, 1991, WB Saunders, pp 33–46. Meek LA: Intraocular silicone prosthesis in a horse, J Am Vet Med Assoc 193:343–345, 1988. Michau TM, Gilger BC: Cosmetic globe surgery in the horse, Vet Clin North Am Equine Pract 20:467–484, 2004. Muir WW: Local anesthesia in ruminants and pigs. In Schrefer J editor: Handbook of Veterinary Anesthesia, ed 4, St. Louis, 2005, Mosby, pp 72–99. Mun˜oz E, Leiva M, Naranjo C, Pen˜a T: Retrobulbar dermoid cyst in a horse: a case report, Vet Ophthalmol 10:394–397, 2007. Murphy CJ, Brooks DE, Kern TJ, Queensberry KE, Riis RC: Enucleation in birds of prey, J Am Vet Med Assoc 183:1234–1237, 1983.

Noordsy JL: Food Animal Surgery, ed 3, Trenton, NJ, 1994, Veterinary Learning Systems, pp 82–85. Pizzirani S, Tseng F, Pirie C: Evisceration in three species of owls. In Proceedings of the 39th Annual Meeting of the American College of Veterinary Ophthalmologists: Abstract 25, 2008. Provost P, Ortenberg AI, Caron JP: Silicone ocular prosthesis in horse: eleven cases 1983–1987, J Am Vet Med Assoc 194:1764–1766, 1989. Ramsey DT, Fox DB: Surgery of the orbit, Vet Clin North Am Small Anim Pract 27:1215–1264, 1997. Riggs C, Whitley RD: Intraocular silicone prosthesis in a dog and a horse with corneal lacerations, J Am Vet Med Assoc 196:617–619, 1990. Rubin LF: Large animal ophthalmic surgery. In Jennings P Jr, editor: The Practice of Large Animal Surgery, vol II, Philadelphia, 1984, Saunders, pp 1151–1201. Schulz K: Field surgery of the eye and paraorbital tissues, Vet Clin North Am Food Anim Pract 24:527–534, 2008. Severin GA: Severin’s Veterinary Ophthalmology Notes, ed 3, Fort Collins, 1996, Colorado State University Press, pp 486–498. Theon AP, Pascoe JR, Carlson GP, Krag DN: Intratumoral chemotherapy with cisplatin in oily emulsion in horses, J Am Vet Med Assoc 202:261–267, 1993. Townsend WM: Food and fiber-producing animal ophthalmology. In Gelatt KN editor: Veterinary Ophthalmology, ed 4, Ames, 2007, Blackwell, pp 1275–1335. Turner AS, McIlwrath CW: Techniques in Large Animal Surgery, Philadelphia, 1982, Lea & Febiger, pp 293–296. Turner LM, Whitley RD, Hagar D: Management of ocular trauma in horses. Part 2: orbit, eyelids, uvea, lens, retina, and optic nerve, Mod Vet Pract 67:341–347, 1986.

CHAPTER

5

Surgery of the eyelids Kirk N. Gelatt1 and R. David Whitley2 1

Small animals; 2Large animals and special species

Chapter contents Introduction

89

Entropion in sheep

Anatomy

90

Preoperative examination procedures

93

Entropion and periocular fat pads in the Vietnamese potbellied pig (Sus scrofa)

113

Surgical considerations of the eyelids

94

SURGICAL PROCEDURES FOR ECTROPION

114

Surgical instrumentation

95

Ectropion in the horse

117

Surgical preparations of the eyelids

95

Tarsorrhaphy in small animals

95

Surgical procedures for combined ectropion and entropion

117

Tarsorrhaphy in the horse

97

OTHER SURGICAL PROCEDURES

120

Aftercare for eyelid surgery in the horse

97

Surgical procedures to decrease palpebral fissure size

120

Lateral canthotomy

98

Surgical procedures to increase palpebral fissure size

122

Surgical procedures for eyelid agenesis

98

Nasal fold trichiasis and resection in dogs

123

Surgical treatment of chalazion

123

Surgical repair of eyelid lacerations

123

Surgical procedures for minor eyelid neoplasms in small animals

126

Reconstructive blepharoplasty after removal of eyelid masses in small animals

128

Surgeries for eyelid neoplasia in the horse

132

Blepharoplastic procedures for the horse

133

Bovine eyelid surgery

137

Surgical procedures for distichiasis

100

Surgical procedures for ectopic cilia

103

SURGICAL PROCEDURES FOR ENTROPION IN SMALL ANIMALS

103

Non-surgical treatment of entropion

103

Surgical management of entropion

105

Postoperative management and complications

111

ADAPTATIONS IN LARGE ANIMALS AND SPECIAL SPECIES

112

Entropion in horses

112

Introduction Eyelid diseases are common in dogs and horses, and infrequent in cats and cattle. In contrast to most ophthalmic diseases, the initial clinical management of eyelid disorders is usually surgery. Traditionally, eyelid diseases are divided into congenital and developmental, inflammatory, traumatic, and neoplastic. The clinical management of all of these groups of eyelid diseases, except for the inflammatory types, is surgery. Surgical treatment may also be indicated for the inflammatory eyelid diseases, after resolution with antimicrobial therapy, to restore the eyelid contours and function associated with the excessive postinflammatory scarring and distortion.

113

Diseases of the canine eyelids Congenital and developmental eyelid disorders in dogs, including entropion, ectropion, distichiasis, and trichiasis, may be treated by a number of different surgical procedures. Selection of the surgical technique for a particular condition may be influenced not only by the most effective procedure, but also by the experience of the surgeon and the surgical instrumentation available. In older dogs eyelid neoplasms are common. Although a significant percentage of the canine eyelid neoplasms are malignant histologically, local recurrence after surgical excision is infrequent. The majority of canine eyelid neoplasms can be excised by reasonably simple surgical procedures.

5

Surgery of the eyelids

Diseases of the feline eyelids Eyelid surgery in cats is less frequent, but just as challenging. Eyelid agenesis occurs not infrequently in the cat, usually affecting the lateral aspects of the upper eyelid. Several eyelid surgical procedures have been developed to treat this condition. Eyelid neoplasms in cats are usually malignant histologically and clinically. Surgical intervention is often combined with radiation, cryotherapy, or other types of therapy for best results. Eyelid trauma occurs in the cat, and as one would expect, is most frequent in young animals. The eyelid trauma may be minor or extensive, and fortunately loss of substantial portions of the eyelids is rare. Although traumatized eyelids may exhibit marked swelling and multiple lacerations, the extensive vascularity of the eyelids usually protects against tissue ischemia and necrosis. As a result, excision and liberal trimming of traumatized eyelid tissues prior to repair are unnecessary and discouraged. Reapposition of severely traumatized eyelids usually yields better postoperative results than excision of still attached but lacerated lid tissues and subsequent reconstructive blepharoplastic surgical procedures to repair these defects.

Anatomy The morphology of the eyelids in domestic animals is quite similar, with size being the major variable. The eyelids represent the transition of the integument system and the beginning of the ophthalmic apparatus with the initiation of the palpebral conjunctiva. The eyelids surround the palpebral fissure, through which the eye contacts the environment. The eyelids are divided clinically into the dorsal, superior, or upper eyelid; the ventral, inferior, or lower eyelid; the medial or nasal canthus; and the lateral or temporal canthus (Fig. 5.1). The dorsal eyelid is the largest, most mobile, and 2–5 mm longer than the lower lid. Distinct ligaments, the septum orbitale, and certain muscles attach at both sides of the palpebral fissure, resulting in an oval rather than round eyelid opening. The medial canthal eyelid area is relatively fixed to the subcutaneous tissues and periosteum by the medial palpebral or canthal ligament. Protected immediately behind the medial canthal ligament is the nasolacrimal sac. The lateral canthal region is more mobile, especially in dogs. The lateral canthal ligament is poorly developed in the dog and is replaced by the retractor anguli oculi lateralis muscle. Hence in dogs, defects often affect the lower lid and lateral canthus.

Diseases of the equine eyelids Developmental lid diseases, such as entropion and ectropion, occur rarely in horses; however, trauma and neoplasia occur not infrequently and are often treated by surgery. Like other animal species, eyelid trauma occurs more frequently in young animals, and maintenance of lid function and preservation of the lid margin are most important. Both squamous cell carcinoma and sarcoid neoplasms commonly involve the eyelids in middle-aged to aged horses, and often surgery is combined with other modalities used to treat these neoplasms and achieve higher success rates.

Diseases of the bovine eyelids Of the different lid diseases, only neoplasia warrants not infrequent lid surgery in this species. Squamous cell carcinoma is the most frequent neoplasm in cattle, and occurs in cattle directly related to aging. The average age of the Hereford breed affected with squamous cell carcinoma is about 7–8 years. Lack of lid and conjunctival pigmentation is also associated with this tumor.

Eyelid skin, cilia (eyelashes), and glands The skin of domestic animal eyelids is thinner than other parts of the integument system (Fig. 5.2). Eyelid movements require both thin and pliable skin. Fine short hairs normally cover the eyelid skin. The subcutaneous tissues under the eyelid skin are relatively thin and attach the lid skin to the deeper orbicularis oculi muscle. Cilia or eyelashes occur primarily on the canine upper eyelid, usually in two or four irregular rows. These cilia are usually the same color as the adjacent eyelid hair coat. Long tactile hairs (pili supraorbitales or vibrissae) appear as a tuft along the dorsal medial orbital margin in several animal species. Eyelashes are not present in cats, although the eyelid hair next to the dorsal eyelid margin may be considered a substitute. Two types of gland, the glands of Moll and glands of Zeis, are located about the cilia follicles. The gland of Moll is a modified sweat (apocrine) gland and the gland of Zeis is a modified sebaceous gland. These glands can become inflamed and abscessed in young animals, resulting in the formation A G

Adaptations from eyelid surgeries in humans The early small animal eyelid surgical procedures were adapted from techniques performed in humans. Human eyelids are quite similar to those in domestic animals, with one major difference: in humans the tarsal layer consists of a distinct cartilaginous plate that provides internal support for the eyelids; in domestic animals the tarsal plate has been replaced by a thinner and more flexible fibrous tarsus. As a result, the eyelids of animals have less internal support, and contact with the anterior portion of the globe is more important to maintain their contours and position.

90

C

D F

E

B

Fig. 5.1 The canine eyelids are divided into upper lid (A), lower lid (B), medial canthus (C), and lateral canthus (D). Other important areas include the nictitating membrane (E), caruncle (F), and cilia (G).

Anatomy

Levator anguli oculi medialis Frontalis

A

Orbicularis oculi

D E

B

F Retractor anguli oculi lateralis

C

Pars palpebralis

G

Fig. 5.2 The different layers of the upper eyelid include: skin (A), orbicularis oculi muscle (B), tarsus (C), insertion of the levator palpebrae superioris muscle (D), meibomian glands (E), palpebral conjunctiva (F), and the cilia (G).

of a stye or external hordeolum. The margo-intermarginalis represents the free margin of the eyelids.

Eyelid muscles The second layer of the eyelids is the muscle layer which consists of several muscles that either close or open the palpebral fissure. The orbicularis oculi muscle is the predominant muscle involved in closure of the palpebral fissure in domestic animals. This muscle encircles the entire palpebral fissure and is attached by the septum orbitale to the medial and lateral canthi. It is divided into the inner pars palpebralis and the outer pars orbitalis. Both the origin and insertion of the orbicularis oculi muscle is the medial palpebral ligament. This muscle is immediately beneath the skin layer, and surgical procedures for entropion (inversion of the eyelid margin) and ectropion (eversion of the eyelid margin) directly involve this muscle. In large animal species the orbicularis oculi muscle is very powerful, especially when ophthalmic pain is present. In large animals, local nerve blocks of the palpebral nerve branch of the auriculopalpebral nerve (branch of the facial nerve) is often necessary to relax this muscle to adequately examine and even treat a painful eye. Several muscles are involved in opening the eyelids and increasing the size of the palpebral fissure in the dog and cat. In the canine upper eyelid these muscles consist of (medial to lateral) the levator anguli oculi medialis, levator palpebrae superioris, and the frontalis, and in the lower lid, the pars palpebralis of the sphincter colli profundus (Fig. 5.3). The levator palpebrae superioris muscle has its origin deep within the orbit, along with the rest of the extraocular muscles, and lies immediately above the dorsal rectus muscle that inserts several millimeters from the dorsal limbus of the globe. Fascial attachments between the dorsal rectus and levator palpebrae superioris muscles result in simultaneous upper movements of the globe and retraction

Fig. 5.3 Muscles that control the size of the palpebral fissure in the dog include: orbicularis oculi (close), levator anguli oculi medialis (open), frontalis (open), retractor anguli oculi lateralis (open), and pars palpebralis (open). Mu¨ller’s muscles (open) and levator palpebrae superioris (open) are not shown.

of the upper eyelid. The levator palpebrae superioris muscle seems to be the most important muscle for upper lid retraction as damage to this muscle or its insertions into the tarsal layer results in ptosis (or drooping of the upper eyelid). The levator anguli oculi medialis muscle elevates the medial upper eyelid and erects the long tactile hairs of the eyebrow. In some of the large breeds of dogs, the action of this muscle results in a noticeable notch at the junction of the medial and middle one-thirds of the upper lid. In the dog, Mu¨ller’s smooth muscle fibers, innervated by the sympathetic nerves, attach to the upper tarsus; in the cat, these muscle fibers also attach to the nictitating membrane. With the release of endogenous adrenaline (epinephrine), or during the fightand-flight reflex, these adrenergic innervated smooth muscle fibers can immediately increase the size of the palpebral fissure. In the cat, the major muscle for closing the palpebral fissure is the orbicularis oculi. The corrugator supercilii medialis raises the majority of the upper eyelid, but laterally the frontoauricularis helps to elevate the upper lid. Lateral and as a substitute for the lateral canthal ligament, the corrugator supercilii lateralis elongates the palpebral fissure. The lower eyelid is relatively fixed and only the orbicularis oculi is present to close the palpebral fissure. In the horse, the anatomy of the eyelids follows the other mammalian patterns. The upper lid is considerably larger than the lower lid and contributes most of the lid motility. The lacrimal puncta are about 2 mm in diameter and about 8 mm from the medial canthus. The medial canthus can be prolonged medioventrally and possesses a prominent, occasionally pigmented, caruncle. The upper lid possesses about 40–50 meibomian glands dorsally and 30–35 glands ventrally. In cattle, the eyelids are quite similar to the horse. They are very thick and strong! The orbicularis oculi is often in small bundles and extends to the edge of the lid margin. The orbicularis oculi is attached medially to the strong medial palpebral ligament and lacrimal bone. Although cattle possess a small and weak lateral palpebral ligament, entropion and ectropion occur rarely in cattle. There are

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Corrugator supercilii medialis

Frontoauricularis

Dorsal portion of orbicularis oculi

Ventral portion of orbicularis oculi

Corrugator supercilii lateralis (retractor anguli oculi)

Fig. 5.4 Muscles that control the size of the palpebral fissure in the cat include: orbicularis oculi (close), corrugator supercilii lateralis (open), frontoauricularis (open), and corrugator supercilii medialis (open). Mu¨ller’s muscles (open) are not shown.

about 32–34 meibomian glands in the upper lid and 26–28 in the ventral lid. The upper fornix measures about 36 mm from the upper lid margin, and the lower fornix is 22 mm from the lower lid margin. The lateral palpebral or canthal ligament is poorly developed in dogs and cats, and usually consists of an irregular thickened lateral septum orbitale. In the large breeds of dogs the lack of or a poorly developed lateral canthal ligament contributes directly to lateral canthal lid diseases in these breeds. The major component of the lateral canthal support system has been replaced by the retractor anguli oculi lateralis (dog) or corrugator supercilii lateralis (cat) muscle (Fig. 5.4). This results in a somewhat mobile but unstable lateral canthus in dogs, and contributes to the frequent involvement of the lateral canthus and lateral lower and upper eyelids with entropion and ectropion. The lateral one-half of the lower eyelid in the dog also has the pars palpebralis muscle, a subdivision of the sphincter colli profundus muscle, which can depress the lateral lower lid.

Eyelid tarsal layer and glands The eyelid skin and tightly adherent muscle layers are easily separated surgically from the deeper two layers, the fibrous tarsus containing the tarsal or meibomian glands and the inner palpebral conjunctiva. The fibrous tarsus provides some infrastructure for the eyelids, but not to the extent that the tarsal hyaline plate does in humans. The fibrous tarsus has fascial attachments to the septum orbitale, resulting in a strong connection to the periosteum of the orbital rim, and a significant barrier for trauma, surgery, and external infectious agents to enter the orbit. The fibrous tarsal layer is also in intimate contact with the medial palpebral or canthal ligament, the base of the nictitating membrane, and the lateral canthus. The medial palpebral ligament is more distinct than the lateral ligament in the dog, and consists of a fibrous band originating from the periosteum of the frontal bone that inserts into the upper and lower tarsal layers. The medial palpebral ligament also serves as the origin and insertion for the circular orbicularis oculi muscle, which undoubtedly assists in the medial movement of tears on the cornea and within the conjunctival sacs. In the

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middle section of the upper eyelid the levator palpebrae superioris muscle inserts into the tarsal layer. The superior and inferior tarsal muscles are smooth muscles in the dog within the endorbita that inserts into the tarsus. These muscles are under sympathetic innervation and help maintain the palpebral fissure open. The tarsal or meibomian glands are sebaceous (holocrine) types and produce the important outer lipid or oily fraction of the preocular or precorneal film. The lipid layer of the preocular film prevents evaporation of the thicker aqueous layer and stabilizes the preocular film. The number of tarsal glands in each lid ranges from 20 to 40, with the upper eyelid containing more glands. The orifices of the tarsal or meibomian glands empty onto the center of the eyelid margin. This area is referred to the ‘gray line’ and is an important surgical zone. The tarsal glands are occasionally visible through the palpebral conjunctiva, and extend for 3–5 mm into the lid substance. The tarsal glands seem able to undergo metaplasia and form additional cilia, called distichia. At the medial canthus at the junction of the upper and lower lids, and at the base of the nictitating membrane, is the lacrimal caruncle. Small fine hairs emerge from its surface, which can act as a wick for tears to moisten the medial canthal skin. The lacrimal caruncle also contains small sebaceous glands.

Palpebral conjunctiva Like the skin and muscle layers of the eyelid, the fibrous tarsus and palpebral conjunctiva are in close contact and difficult to separate surgically. The palpebral conjunctiva starts at the eyelid margin, and continues to the conjunctival fornix to join the bulbar conjunctiva. The palpebral conjunctival surface at the eyelid margin consists of non-keratinized stratified epithelium, but approximately one-third the distance from the lid margin to the conjunctival fornix it changes into pseudostratified epithelium. Once the pseudostratified epithelial layer is established, goblet cells that produce mucin begin to appear. The highest concentrations of goblet cells occur in the conjunctival fornices. Like the cornea, the palpebral conjunctiva is also coated with preocular film to facilitate eyelid movement over the cornea, and to minimize trauma between the bulbar and conjunctival epithelial surfaces.

Anatomy of the equine eyelid Muscles that open the equine eyelids include the levator palpebrae superioris, Mu¨ller’s, levator anguli oculi medialis, frontalis, and malaris. The levator palpebrae superioris muscle, along with the levator anguli oculi medialis muscle, raises the upper eyelid. Mu¨ller’s muscle is a smooth muscle that originates from the posterior surface of the levator muscle in the upper eyelid and from the ventral rectus muscle for the lower eyelid. It is innervated by sympathetic fibers that travel with the ophthalmic branch of the fifth cranial nerve. Mu¨ller’s muscle inserts on the tarsus and, along with other muscles, keeps the palpebral fissure open. It is the muscle, when innervation is interrupted in Horner’s syndrome, that results in ptosis of the upper eyelid. The frontalis muscle inserts laterally on the upper eyelid. The malaris muscle inserts on the ventral orbicularis oculi muscle and

Preoperative examination procedures

functions to open the lower eyelid. The upper eyelid is the more mobile and larger section of the eyelids. It provides the majority of the blinking function. Sensory innervation of the eyelids is via the ophthalmic and maxillary branches of the trigeminal (fifth cranial) nerve. The ophthalmic portion branches into the frontal, lacrimal, and nasociliary nerves. The frontal branch passes anteriorly from the orbit through the supraorbital foramen. It then becomes the supraorbital nerve, dividing over the forehead and innervating most of the upper eyelid. The lacrimal nerve innervates the lacrimal gland and the upper eyelid at the lateral canthus. The nasociliary branch gives rise to the infratrochlear nerve, which provides sensory innervation to the medial canthus, caruncle, nictitating membrane, upper and lower conjunctiva, and nasolacrimal puncta and ducts. The remainder of the lower eyelid is innervated by the zygomatic nerve, which is a branch of the maxillary nerve.

temporal artery. Additional blood supply to the lateral canthus and upper eyelid is derived from the lacrimal and dorsal muscular branch arteries, and the lower eyelid by the zygomatic artery, all branches from the external ethmoidal artery. The medial aspects of the canine eyelids are supplied by branches of the malaris artery, a branch of the infraorbital artery, which anastomose with the inferior palpebral and transverse facial arteries, and branches of the external ophthalmic artery. Limited blood supply to the eyelids is also provided from small vessels within the septum orbitale and conjunctival fornices that originate from the deeper orbital blood vessels. The lymphatic drainage from the eyelids converges at the medial and lateral canthal areas. Lymphatic drainage appears to mainly involve the parotid lymph node. However, some of the same areas may drain to the mandibular lymph nodes. As a result, both lymph nodes need to be accessed clinically if regional metastases from eyelid neoplasms are suspected, particularly in horses and cattle.

Eyelid sensation Most of the sensation of the animal eyelids is provided by several branches of the trigeminal nerve. Sensation of the lateral two-thirds of the upper eyelids is provided by the trigeminal nerve through its frontal nerve and its branch, the supraorbital nerve, and the medial canthus by the infratrochlear nerve. The medial canthus and medial aspects of the upper eyelids are also served by the nasociliary nerve, the largest branch of the ophthalmic nerve. The sensation for the entire lower eyelid is provided by the maxillary division of the trigeminal nerve through its zygomaticotemporal branch.

Eyelid innervation The palpebral branch of the facial or seventh cranial nerve innervates the majority of the muscles that control palpebral fissure size, except for the levator palpebrae superioris muscle that, along with most of the extraocular muscles, is innervated by the oculomotor or third cranial nerve. The pars palpebralis muscle of the lateral lower eyelid of the dog is innervated by the dorsal buccal branch of the facial nerve. In horses, the auriculopalpebral nerve and its branches (branch of the facial nerve), as well as the supraorbital nerve (branch of the ophthalmic division of the trigeminal nerve, sometimes referred to as the frontal nerve), are common sites for local nerve blocks in the horse to provide akinesia (auriculopalpebral nerve) and local analgesia (supraorbital nerve) to the upper lid. In most animal species the rostral aspect of the palpebral nerve can be blocked a few centimeters caudal of the lateral canthus. In this forward position, movement of the upper lid may persist.

Eyelid blood supply and lymphatics The blood supply to the eyelids is derived from several sources, but primarily originates from the medial and lateral canthal areas for both eyelids. The lateral aspects of both eyelids in the dog are supplied by the lateral dorsal and lateral ventral palpebral arteries from the superficial

Eyelid function The functions of the eyelids are numerous and include: 1) protection of the eye; 2) entrapment of material before it contacts the conjunctiva and cornea; 3) production of glandular secretions by the tarsal or meibomian glands, a vital component of the preocular film; 4) distribution of the preocular film and tears across the corneal and conjunctival surfaces; 5) medial movements of tears toward the lacrimal puncta for exit via the nasolacrimal drainage apparatus; and 6) provision of the blink reflex to tactile stimuli applied to the cornea, conjunctiva or nictitating membranes, or following a strong light and/or loud noise. When direct stimuli are applied to the eyelids, conjunctival and corneal surfaces, the eyelids blink. This reflex is subcortical, involving the ophthalmic division of the trigeminal nerve (afferent portion) and palpebral division of the facial nerve (efferent portion). A strong light source directed at the eye will not only initiate a light-induced pupillary response (a subcortical reflex), but also a blink response (also a subcortical function).

Preoperative examination procedures In the assessment of the eyelids preoperatively, their structure, function (blink reflex), and relationship to the face, each other, and to both eyes are carefully evaluated. Adequate illumination and some magnification are essential. The head loupe or magnifier and Finoff transilluminator, or portable slit-lamp biomicroscope are the best instruments that combine these two characteristics. The eyelids, eye, and orbit relationships can also be influenced by the presence of pain, inflammation, enophthalmia or exophthalmia, body condition, age, dehydration, and muscle condition. Not infrequently, the eyelids cannot be restored surgically to completely normal appearance and function because of these other variables, especially the position of the globe. These complex relationships of the eyelids, eye, and orbit in the dog also impede genetic studies of the eyelid diseases. The animal eyelids normally rest on the cornea and bulbar conjunctiva. If the globe is recessed into the orbit, eyelid contact may not be possible and instability of the lower

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eyelid results. The usual result is entropion or an inversion of the eyelid margin and substance. This phenomenon occurs commonly in certain breeds of dogs, foals, and in aging animals (probably associated with loss of orbital fat). Secondary blepharospasm is a common component of most painful eyelid conditions. With eyelid swelling, the eyelid margin usually rolls inward. When the outer eyelid margin, normal cilia (eyelashes), and trichiasis (involving the normal eyelid hair) touch the bulbar conjunctiva, cornea or a combination of both surfaces, the animal reacts by developing secondary blepharospasm. The resultant trigeminal– facial nerve reflex usually worsens the eyelid defect even further, and produces additional irritation and pain. This protective eyelid reflex then produces an ever-increasing cycle of pain and blepharospasm. Hence, in many painful eyelid diseases, the initial structural disease is aggravated by a normally protective eyelid closure reflex. Animals often respond to localized ocular pain by rubbing, which can cause additional localized swelling and even loss of skin integrity. Therefore, in the examination of eyelid diseases that are potential candidates for surgical correction, surgery should be directed at only the underlying structural eyelid disorder. To estimate the extent of secondary blepharospasm in a patient, a few drops of topical anesthetic are instilled onto the cornea and conjunctiva after the initial entropion has been estimated. After 3–5 min, the secondary blepharospasm will usually be relieved, and the basic structural eyelid abnormality can be ascertained. Surgical correction should be directed at only this anatomic eyelid abnormality. The defect is usually undercorrected slightly (about 0.5–1 mm) to accommodate postoperative fibrosis. Infrequently, the eyelid defect can become so painful and the eyelid and associated tissues so inflamed that multiple instillations of topical anesthetic will not totally suppress secondary blepharospasm. In these patients, localized regional eyelid block of the palpebral nerve can be administered. In the dog, a few milliliters of local anesthetic are injected subcutaneously along the dorsal aspects of the middle portion of the zygomatic arch to block the palpebral branch of the facial nerve and the primary innervation to the orbicularis oculi muscle that closes the palpebral fissure (Fig. 5.5). Within a few minutes, total loss of eyelid muscle Fig. 5.5 To perform the palpebral nerve block and produce lid akinesia in most animal species, 3–5 mL of local anesthetic are injected subcutaneously on the dorsal aspect of the middle portion of the zygomatic arch or just caudal of the lateral canthus.

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tone will occur, and the extent of the eyelid problem to be corrected surgically can be determined. In the horse, the auriculopalpebral nerve can be blocked at at least two sites (see Fig. 3.5, p. 44). The auriculopalpebral nerve can be blocked by infiltrating local anesthetic in a fan-like manner subfascially in the depression just caudal to the posterior ramus of the mandible at the ventral edge of the temporal portion of the zygomatic arch. The hypodermic needle is directed dorsally just caudal to the highest point of the arch. Before injecting local anesthetic, aspiration is performed to prevent injection into the rostral auricular artery or vein. This procedure may also result in akinesia of the ear muscles as well as gravitate ventrally and affect other branches of the facial nerve. Within a few minutes, total loss of eyelid muscle tone will occur, but lid sensation is still present. The second palpebral nerve block in the horse blocks multiple branches of the palpebral nerve closer to the eye. Local anesthetic is injected subcutaneously at the highest point of the dorsal border of the zygomatic arch. The supraorbital nerve of the horse is often blocked at the supraorbital foramen to provide akinesia to the forward branches of the palpebral nerve, as well as local anesthesia by blocking the supraorbital nerve, a branch of the trigeminal nerve. This procedure is often used prior to ophthalmic examinations, insertion of dorsal subpalpebral medication systems, and excision of upper eyelid masses. In cattle, the palpebral nerve can be blocked by injecting 3–5 mL of local anesthetic about 4–6 cm caudal of the lateral canthus.

Surgical considerations of the eyelids The upper and lower eyelids share most functions, but also have some unique characteristics. The upper eyelid covers the majority of the cornea, and blinks at a normal rate of about 15 times per minute. Only part of these blink reflexes cover the entire cornea. The upper eyelid has the levator palpebrae superioris muscle that originates from the depths of the orbit above the dorsal rectus muscle. The upper eyelid is primarily responsible for the cosmetic appearance, while the lower eyelid margin serves to collect and prevent the

Tarsorrhaphy in small animals

preocular film and tears from overflowing onto the lower canthi and eyelid surfaces. Surgical and traumatic interruption of the palpebral nerve innervation to the eyelids results in exposure keratitis if upper, rather than lower, eyelid function is impaired. The upper eyelids are larger and longer than the lower lids, and are the principal source for tissues for reconstructive surgical procedures of the eyelids. The higher number of tarsal or meibomian glands occurs in the upper eyelid. Only the canine upper eyelid contains cilia (eyelashes). Although the autogenous transplantation of cilia has not been reported in domestic animals, the surgical technique is not difficult. Hence, surgery of the upper eyelids must consider movements, protection of the eye, and appearance, whereas surgery of the lower eyelids must primarily address the collection, retention, and medial movement of tears. After extensive blepharoplasty, the eyelids (especially the upper) may function poorly for several days to weeks because of lid swelling and possible nerve impairment. To protect the cornea and prevent ulceration, a temporary complete tarsorrhaphy is necessary until a normal blink response returns. The conjunctival cul-de-sac or fornix is considerably larger for the dorsal eyelid, probably to accommodate ventral rotation of the globe. The lower conjunctival fornix is more shallow but is the primary receptacle for the tears and, assisted by the intermittent movements of the orbicularis oculi muscles, gradually propels the tears medially toward the lacrimal puncta. As indicated in an earlier section, the surgical anatomy of the eyelids is usually divided into two layers: the skin and muscle layer, and the deeper tarsus and palpebral conjunctiva. The thin elastic eyelid skin has limited subcutaneous tissue and attaches directly to the orbicularis oculi muscle. Surgical separation of the eyelid skin from the deeper muscle layer is tedious and, in small species, often very difficult. Within the eyelid margins are the numerous orifices of the tarsal or meibomian glands. This area is referred to as the ‘gray line’, an area to surgically split or divide the eyelids longitudinally, as well as for the placement of eyelid sutures that will not contact and directly damage the cornea.

Surgical instrumentation The instrumentation for eyelid surgery usually consists of a mixture of general soft tissue instruments, as well as selected ophthalmic instruments. The recommended ophthalmic instruments include small straight and curved strabismus or tenotomy scissors to cut tissues and sutures, both teeth (1  2) and serrated thumb forceps (such as Bishop–Harmon forceps), small scalpel blades (Nos 6400 and 6500 microsurgical), small wire eyelid speculum, and a standard ophthalmic needle holder (often with lock). Special thumb forceps, such as chalazion and entropion forceps, are useful to clamp and stabilize the eyelids during surgery (see Table 1.3, p. 12). Suture selection is variable and often at the surgeon’s discretion. Sutures for the tarsus and palpebral conjunctiva are usually absorbable (polyglycolic or polyglactic acid, and polydioxanone), and the simple continuous pattern is usually used. The knots should be buried beneath the palpebral conjunctiva to avoid direct contact with the cornea. Sutures

involving the eyelid skin and superficial aspects of the orbicularis oculi muscle are usually non-absorbable and the simple interrupted pattern. Many veterinary ophthalmologists prefer 4-0 to 6-0 silk; if corneal contact with the silk suture occurs, no irritation or damage results. Although tissue reactivity with silk can be a problem, and braided silk is a potential wick for bacterial invasion, eyelid suture removal at 7–10 days postoperatively effectively avoids these potential problems. The other frequently used nonabsorbable suture is 4-0 to 6-0 nylon. Choice of atraumatic swaged-on cutting needles is quite variable; however, the one-fourth to three-eighths curved needles are most useful. Hemostasis is usually provided by small curved mosquito hemostats or point cautery. Vessel ligation with absorbable sutures is infrequent as these areas may develop focal postoperative fibrosis that may influence the surgical result. Point cautery is usually preferred, but used judiciously. Sterile cotton-tipped applicators and cotton surgical sponges can effectively maintain most eyelid surgical fields clear of hemorrhage. Moistening with 1:10 000 or other dilutions of adrenaline (epinephrine) may be helpful. Hemostasis is also provided when the eyelids are grasped and held with chalazion and entropion forceps.

Surgical preparations of the eyelids Surgical preparation of the eyelids is usually performed immediately before surgery. Sometimes the patient is on therapy with topical antibiotics or antibiotics/corticosteroids for treatment of the eyelid disorder, and the same therapy is continued immediately after surgery. The high vascularity of the eyelids promotes healing and often topical corticosteroids are administered perioperatively to control the local inflammation and swelling. A bland petroleum ointment may be placed on the corneal and conjunctival surfaces to collect debris and hair during the surgical preparation. The ointment is carefully removed by sterile cotton-tipped applicators immediately before surgery. The eyelid hair is carefully removed by small hair clippers or shaved. The eyelid skin is thin and, if traumatized during hair removal, swelling may result. The surgical preparation of choice is 0.5% povidone– iodine solution as contact with the cornea is not irritating. At least three scrubs are recommended to clean and reduce the local microbial population. After these scrubs, the area is liberally rinsed with 0.9% sterile saline. Alcohol and other traditional surgical preoperative measures are not recommended as contact with the cornea and conjunctiva can be very irritating and damaging to their epithelia. Draping is performed with four small cotton towels positioned around the palpebral fissure and covered with a surgical drape. Small towel clamps or bulldog clamps may be used to secure the drapes, but should be used sparingly.

Tarsorrhaphy in small animals In the tarsorrhaphy procedure the eyelids are apposed either temporarily or permanently, and the lid apposition may include part or all of the upper and lower eyelids. In the permanent tarsorrhaphy procedure part of the eyelid

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margins of the upper and lower eyelids are excised and, after apposition by sutures, the eyelids should remain sealed. Complete permanent tarsorrhaphies are part of the enucleation and exenteration procedures after removal of the eye and the orbital contents. Partial permanent tarsorrhaphies are indicated to treat long-term ocular disorders, such as neuroparalytic keratitis, neurotropic keratitis, lagophthalmia, and chronic exposure keratitis. In the temporary tarsorrhaphy technique the eyelid margins are apposed by sutures for several days to a few weeks to cover the healing cornea and/or conjunctiva. In the complete temporary tarsorrhaphy method the entire palpebral fissure is closed. In the partial technique, only part (medial, central, or lateral) of the palpebral fissure is closed, thereby permitting vision by the patient, daily inspection by the veterinarian, and topical medication of the eye. The complete temporary tarsorrhaphy is indicated clinically, in part, for the treatment of traumatic proptosis, after most orbitotomies, after many extensive eyelid procedures, after nictitating membrane flaps, after extensive conjunctival surgery, to treat premature opening of the eyelids, to help maintain collagen shields and contact lenses in place, and for the treatment of recurrent corneal erosions and other selected superficial corneal disorders. Complete temporary tarsorrhaphies are also indicated when upper eyelid function is impaired and the development of exposure keratitis is anticipated. The partial temporary tarsorrhaphy is used frequently after conjunctival and corneal surgery to reduce eyelid trauma to the surgical site, and to provide some contact and pressure to fresh grafts. Suture ends in temporary tarsorrhaphies may be left long to facilitate occasional adjustment of the suture pressure, as well as occasional loosening to open the tarsorrhaphy and inspect the eye. The support of a weakened cornea by complete temporary tarsorrhaphy may vary by breed but it does not appear to give as much support as that provided by the nictitating membrane flap or a complete conjunctival graft. However, the complete temporary tarsorrhaphy procedure can supplement these methods to provide additional corneal support. Complete temporary tarsorrhaphy constitutes a barrier to topical medication of an eye, but the subpalpebral system can be inserted in the dorsolateral or lateral conjunctival fornix at the conclusion of surgery to ensure delivery of ophthalmic solutions. The apposed eyelids may also retain the topical solutions in contact with the cornea for longer periods of time, thereby increasing their effectiveness. The permanent apposition of the upper and lower eyelid margins at the medial and lateral canthi is discussed in a later section under surgical procedures to reduce the size of the palpebral fissure. Chronic exposure of the cornea, especially in brachycephalic breeds, may be a major contributing factor in the pathogenesis of recurrent central corneal ulceration, and surgical reduction of the size of the palpebral fissure may significantly reduce the possibility of recurrence.

A

Fig. 5.6 For a lateral permanent tarsorrhaphy. (a) The apposing upper and lower eyelid margins are trimmed by Metzenbaum or Mayo scissors at a depth of 4–5 mm. (b) The lids are apposed by two layers of sutures: the tarsoconjunctival layer with 4-0 to 6-0 simple continuous absorbable sutures placed submucosally, and the orbicularis oculi muscle and skin layer with 4-0 to 6-0 simple interrupted non-absorbable sutures.

entire eyelid margins are excised for 360 , with special care to adequately excise the lid margins at the two canthi. For partial permanent tarsorrhaphy any section of the eyelid may be used, but most often the lateral and medial canthal areas are involved. At a depth of 4–5 mm, the bases of the meibomian glands are excised. The eyelids are usually apposed by two layers of sutures in most dogs (Fig. 5.6b); however, in miniature breeds, a single suture layer may suffice. The deeper tarsopalpebral layer is apposed with either 4-0 to 6-0 simple interrupted or a simple continuous absorbable suture placed submucosally to avoid corneal contact. The eyelid skin–orbicularis oculi layer is usually apposed with 4-0 to 6-0 simple interrupted or interrupted mattress non-absorbable sutures.

Temporary tarsorrhaphy In the complete and partial temporary tarsorrhaphy procedures, 4-0 to 6-0 interrupted mattress non-absorbable sutures are carefully placed in the eyelid margin through or just anterior to the ‘gray line’ to appose the upper and lower lids (Fig. 5.7a). Sutures placed near or within the ‘gray line’ can adequately hold the eyelids together without tearing of the lid margins. Sutures placed within the ‘gray line’ do not penetrate the full thickness of the lid, thereby avoiding direct contact and damage to the cornea. The number of eyelid sutures varies (usually 2–4) depending on whether a

A

Permanent tarsorrhaphy In the permanent tarsorrhaphy procedure the upper and lower eyelid margins are trimmed by curved Metzenbaum scissors 3–5 mm from the lid margins (Fig. 5.6a). This area is usually where the eyelid pigmentation stops and the eyelid hair appears. For complete permanent tarsorrhaphy the

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B

B

Fig. 5.7 For the complete temporary tarsorrhaphy. (a) Three to six 4-0 to 6-0 interrupted mattress non-absorbable sutures are pre-placed in the lids. Stents are used to distribute the tension on the sutures and prevent lid necrosis. (b) The sutures are placed through the ‘gray line’ (or the orifices of the tarsal glands) and outer one-half thickness of the eyelids to avoid touching the cornea and still maintain excellent holding capacity. The sutures are left long to permit occasional adjustments postoperatively.

Aftercare for eyelid surgery in the horse

partial or complete temporary apposition of the eyelids is performed. Because of the tension on the eyelid sutures caused by the muscles effecting opening of the palpebral fissure, stents (consisting of rubber bands, old intravenous tubing, or other material) are used to distribute suture tension, and decrease local lid swelling and the likelihood of pressure necrosis (Fig. 5.7b). The temporary tarsorrhaphy is usually effective for 7–21 days (see Figs 4.25 and 4.26).

Postoperative care and complications after tarsorrhaphy The most frequent postoperative complications after permanent tarsorrhaphy are related to excessive tension on the lid sutures short term, and wound failure long term. As indicated in the eyelid anatomy section, several muscles function to open the palpebral fissure. In the long-term partial permanent tarsorrhaphy procedure, this chronic tension results in gradual weakening and atrophy of the surgical apposition site. Dehiscence within the first few weeks postoperatively is usually repaired by debriding the wound edges and apposition with additional sutures. The most frequent complications immediately after temporary tarsorrhaphy are variable swelling of the eyelids and suture contact with the cornea. Patients with temporary tarsorrhaphies should be examined daily or every other day, as eyelid swelling related to sutures and the preoperative ophthalmic condition may necessitate occasional suture adjustments. If the sutures become too tight, local eyelid necrosis and irritation result. If the sutures become too loose, suture contact and damage to the cornea may occur. Leaving the sutures a little long after performing the temporary tarsorrhaphy procedure permits minor adjustments and avoids these potential problems. Routine use of the E-collar postoperatively in small animals and facial masks in horses is important and effectively prevents self-trauma to the surgical site.

Tarsorrhaphy in the horse A tarsorrhaphy is the apposition of the upper and lower eyelid to each other. The procedure can be temporary or permanent, depending on the expected length of time the tarsorrhaphy is needed. A tarsorrhaphy is used for protection of the cornea in patients with the inability to blink normally, such as in facial nerve paralysis or eyelid swelling. Tarsorrhaphy is indicated after corneal surgery to provide support to the globe, and after eyelid surgery to allow the normal eyelid to act as a splint for the operated eyelid to reduce distortion, cicatrix, and suture line dehiscence.

Temporary tarsorrhaphy in the horse A temporary tarsorrhaphy is used after corneal surgery or eyelid surgery, and is performed after surgery while the horse is maintained under general anesthesia. However, it can easily be performed in the standing horse with sedation, local nerve blocks, and topical ophthalmic anesthetic. Preparation of the periocular area for aseptic surgery should be performed. Three to four horizontal mattress sutures are used (see Fig. 5.7). Most commonly the suture material is

4-0 to 5-0 nylon or proline. Sutures are placed partial thickness through the eyelid margin at the tarsal gland openings. Alternatively, sutures may be placed partial thickness in the eyelid in a pattern parallel to the eyelid margin and tied across the eyelid fissure. The use of stents of sterile intravenous tubing, rubber tubing, sterile rubber bands, or buttons helps to prevent the sutures from cutting into the eyelid tissue.

Permanent tarsorrhaphy in the horse When extended closure for weeks or months is anticipated, such as in facial nerve paralysis, a permanent tarsorrhaphy is performed. It is similar to the temporary tarsorrhaphy except that, prior to placing the sutures, the superficial eyelid margin is excised or debrided to allow adhesion as the tissue heals (see Fig. 5.6). Sutures are removed in 10–12 days, leaving the eyelid margins adhered. The tarsorrhaphy is left in place until the eyelids heal or neurologic function returns. When the tarsorrhaphy is no longer needed, the adhered areas of the eyelid margin are carefully incised with tenotomy scissors to restore the palpebral fissure.

Aftercare for eyelid surgery in the horse The general protocol for aftercare for eyelid surgery is similar to those for skin and reconstructive procedures elsewhere on the body. Often after tarsorrhaphies, the primary condition, such as corneal ulceration or facial nerve paralysis, still requires primary therapy. Preoperative and perioperative topical and systemic antibiotics are indicated. The placement of a subpalpebral lavage system will facilitate topical application of solutions to the eye. Postoperative swelling will be reduced by the administration of systemic non-steroidal anti-inflammatory agents (flunixin meglumine 1 mg/kg IV; BanamineW, ScheringPlough, Kenilworth, NJ) immediately before surgery. Postoperative edema will be lessened by the application of ice packs for the first 24 h after surgery. If swelling is present 24 h after surgery, warm compresses may further reduce the swelling and discomfort at the surgical site. Dimethyl sulfoxide has been applied to the periorbital skin to reduce postsurgical swelling and discomfort. Extreme caution must be exercised to avoid inadvertent contact of this product with the cornea and conjunctiva. If rubbing or self-mutilation is a concern, the surgical site or eye must be protected by a protective hood with a plastic or solid eyecup (EyeSaver™, Jorgensen Laboratories, Loveland, CO.). Cross tying or neck cradles have also been used successfully. In an effort to decrease dust and debris from complicating the suture lines in stabled horses, hay is fed on the ground and hay and bedding may be misted with water to minimize dust. If granulating wounds are present, removal of the exudate once or twice daily, with application of petroleum jelly or a povidone–iodine gel ventral to the wound is helpful, and fly control is essential in warmer climates. Fly control around the horse’s face is achieved by wiping fly repellent around the surgical site, by fitting the horse with a fly mask, or by using fly-repellent strips attached to the halter. Skin sutures are usually removed 8–12 days after surgery. In situations when tension on the suture line cannot be avoided, sutures are left in place for 18–24 days.

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Lateral canthotomy

Surgical procedures for eyelid agenesis

The lateral canthotomy procedure is used to temporarily increase the size of the palpebral fissure and facilitates surgical exposure of the globe. In many prominent-eyed breeds of dogs and for most cats, a lateral canthotomy for most ophthalmic surgical procedures is not necessary. However, in many mesocephalic and nearly all dolichocephalic breeds of dogs, lateral canthotomy is indicated for most corneal and intraocular surgeries. After insertion of an eyelid speculum, the palpebral fissure is maximized and the surgical exposure ascertained. If additional exposure is necessary, a lateral canthotomy is performed with heavy-duty straight or curved Mayo scissors (Fig. 5.8a). The lateral canthal eyelid is incised for 5–15 mm, but the incision should not extend beyond the lateral orbital ligament. Hemorrhage is usually negligible. Point cautery can control any minor bleeding. A straight mosquito forceps may be used to slightly crush the tissues prior to the incision to control hemorrhage but is not usually necessary. At the conclusion of surgery, the lateral canthotomy is usually apposed by one or two layers of sutures. The palpebral conjunctiva, submucosal fascia, and tarsus are apposed with 4-0 to 6-0 simple interrupted absorbable sutures (Fig. 5.8b). The external layer of closure, consisting of the orbicularis oculi muscle and lid skin, is apposed with 4-0 to 6-0 simple interrupted non-absorbable sutures. The first suture is carefully placed at the eyelid margin. Occasionally this first suture is an interrupted mattress or figureof-eight suture. The skin sutures are removed at 7–10 days postoperatively. The most frequent postoperative complications after lateral canthotomy include dehiscence of the first one or two sutures, usually within the first week, and the malalignment of the area. In eyes with lateral canthotomies, postoperative medications and ophthalmic examinations should be performed with care to prevent undue tension on the healing lateral canthus and sutures. Routine use of the E-collar in small animals also assists maintenance of the lateral canthotomy. Animals can quickly traumatize this area and tear the sutures from the lateral canthus. In the event of local dehiscence, the wound edges are refreshened and apposed by additional sutures.

Eyelid agenesis occurs not infrequently in cats, and no breed predisposition has been demonstrated. The condition is rare in dogs and other animal species. In lambs, congenital eye defects generally appear as ‘notches’. In cats, the upper eyelid is most frequently involved. The condition may be uni- or bilateral. The lateral aspects of the upper eyelid are usually affected. In many cats with eyelid agenesis additional ocular anomalies, such as dermoids, iris defects, cataracts, and optic nerve colobomas, may be present. The defect may be inherited, and also associated with factors that influence eyelid and eye development such as infectious feline enteritis or panleukopenia virus. Clinical signs associated with eyelid agenesis include irritation, epiphora, and the absence of the lateral upper eyelid margin and variable amounts of the lid (Fig. 5.9). Often in the area of eyelid agenesis, the remaining lid is inverted, resulting in focal keratitis. Surgical correction of feline eyelid agenesis is recommended if chronic conjunctival irritation and corneal involvement develop. Several surgical techniques may be used to treat eyelid agenesis successfully. The choice of surgical procedure is influenced by the severity of the lid defect and the extent of reconstruction needed to repair the defect. For mild cases, the leading lid tissue that has become inverted can be corrected by the Hotz–Celsus procedure used for entropion. The more severe defects require tissue transposition from distant sites. Several procedures may be performed, including: 1) the skin, orbicularis oculi, and tarsal pedicle graft from the lower to upper lid; 2) the skin, orbicularis oculi, and tarsal pedicle graft combined with conjunctiva grafted from the anterior surface of the nictitating membrane; 3) the Cutler–Beard or bucket handle technique; and 4) the sliding skin graft. All of these surgical techniques are successful but more difficult, and some are two-step procedures. Both pedicle graft procedures will be described in this section. The bucket handle and sliding skin procedures will be presented in a later section on reconstructive blepharoplasty. As the most frequent form of eyelid agenesis involves the margin and limited amounts of the lid per se, pedicle grafts

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Fig. 5.8 Lateral canthotomy increases exposure of the globe. (a) After placement of the wire eyelid speculum to ascertain exposure, the lateral canthus is incised by curved Mayo scissors for 5–15 mm. The length depends on the breed and required amount of exposure. (b) Two-layer closure includes: tarsoconjunctiva with 4-0 to 6-0 simple continuous absorbable suture and the orbicularis oculi–skin layer with 4-0 to 6-0 simple interrupted non-absorbable sutures. The first suture is carefully placed at the lid margin.

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Fig. 5.9 Eyelid agenesis, affecting the lateral one-half of the upper lid, in a cat. Secondary superficial keratitis is also evident.

Surgical procedures for eyelid agenesis

of skin, orbicularis oculi, and tarsus are quite successful. The technique, described by Roberts and Bistner, uses adjacent palpebral conjunctiva to line the deep aspects of the skin– muscle graft. The procedure by Dziezyc and Millichamp lines the inside of the skin, muscle, and tarsal pedicle graft with mucosa from the anterior surface of the nictitating membrane. Both of these techniques may also be used to treat eyelid neoplasms in cats, such as squamous cell carcinomas, that primarily affect the lid margin.

Roberts and Bistner procedure In this method a myocutaneous pedicle of skin, orbicularis oculi muscle, and tarsus are transplanted from the lateral portion of the lower eyelid to the dorsolateral lid defect. With the transposition of the orbicularis oculi muscle, the blink reflex is strengthened and often returned to near normal. After general anesthesia and surgical preparation of both eyelids, the recipient bed of the upper eyelid defect is prepared by dividing the lid skin and tarsus from the palpebral conjunctiva. Dissection of the upper border of the defect should continue toward the conjunctival fornix for 10–15 mm to separate the palpebral conjunctiva sufficiently to line the posterior aspect of the pedicle graft. The eyelid is split into skin–orbicularis oculi muscle, and tarsus– palpebral conjunctiva for a distance of 3 mm into normal eyelid (Fig. 5.10a). A right-angle incision at the nasal end of the defect is prepared by scissors to accommodate the tip of the pedicle graft. The pedicle graft of skin, orbicularis oculi muscle, and tarsus is prepared by scalpel starting

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15 mm lateral of the lateral canthus and 2 mm parallel to the lower eyelid margin (Fig. 5.10b). The second parallel incision should provide a pedicle that is about 0.5–1 mm wider than the height of the upper lid defect. The length of the pedicle varies depending on the length of the upper defect. By scalpel the skin incision is deepened to include the orbicularis oculi muscle and tarsus (Fig. 5.10c,d). The base of the pedicle graft should be wider than its tip to ensure adequate perfusion of the entire pedicle. The pedicle is repositioned to the defect and apposed by two layers of sutures (Fig. 5.10e). The deep layer attaches the recipient and donor tarsus by a 4-0 to 6-0 simple continuous absorbable suture. The skin and orbicularis oculi layers are apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures. The posterior aspects of the pedicle graft must be covered by palpebral conjunctiva, separated during preparation of the graft bed. The new posterior conjunctival lining should not produce any traction on the pedicle graft. The lower eyelid wound is apposed with 4-0 to 6-0 simple interrupted non-absorbable sutures. If traction on the graft is apparent at the conclusion of surgery, a complete temporary tarsorrhaphy is performed to provide counterpressure for 14–21 days. An E-collar should be worn until the healing is complete and all sutures have been removed.

Dziezyc and Millichamp procedure This method not only transplants a lower eyelid myocutaneous pedicle graft to the focal area of lid agenesis, but also requires a pedicle graft of palpebral conjunctiva from

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Fig. 5.10 To treat eyelid agenesis. (a) A pedicle graft of skin, orbicularis oculi muscle and tarsus is transplanted to the dorsolateral lid defect. The upper lid defect is prepared by scissors to separate the skin–orbicularis oculi–tarsus from the palpebral conjunctiva. The palpebral conjunctiva must be adequately dissected to the fornix to ensure posterior cover for the graft without any tension. (b) The pedicle is prepared by incision by scalpel about 2 mm below the lower eyelid margin. The length of the pedicle depends on the length of the upper lid defect. (c) Intraoperative photograph showing the myocutaneous graft, separated from its tarsoconjunctival layer, and ready to attach to the edge of the remaining dorsolateral lid. (d) The pedicle is separated by tenotomy scissors from the deeper palpebral conjunctiva. (e) The tarsal layers of the pedicle graft and defect are apposed with 4-0 to 6-0 simple continuous absorbable sutures. The muscle–skin layers of the graft and defect are apposed with 4-0 to 6-0 simple interrupted nonabsorbable sutures. The adjacent palpebral conjunctiva is apposed to the deep aspect of the pedicle graft by 6-0 simple interrupted absorbable sutures.

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Fig. 5.11 Another technique to treat upper eyelid agenesis in the cat. (a) A lower eyelid pedicle is prepared 5–7 mm below the lid margin by scalpel. The pedicle consists of eyelid skin, orbicularis oculi muscle, and tarsus. The upper lid defect is prepared by tenotomy scissors to receive the graft. (b) A pedicle graft of mucosa is prepared by scissors from the anterior surface of the nictitating membrane to line the posterior aspect of the myocutaneous pedicle lid graft. (c) Both grafts are secured in their positions. For the mucosal graft, 6-0 simple interrupted absorbable sutures are placed. For the external skin–muscle–tarsus graft, 4-0 to 6-0 simple interrupted non-absorbable sutures are used. The conjunctival graft base can be transected 3–4 weeks postoperatively.

the anterior surface of the nictitating membrane. The initial lower eyelid pedicle graft is prepared, as in the Roberts and Bistner method, but further (5–7 mm) from the lower eyelid margin (Fig. 5.11a). The graft bed is prepared to receive the lower lid graft. Both the pedicle’s length and width should be at least 1 mm greater than the defect. By scissors the graft of skin, orbicularis oculi muscle, and tarsus are separated from the underlying palpebral conjunctiva. The graft and the defect edges are apposed with 4-0 to 6-0 simple interrupted non-absorbable sutures. A pedicle graft of palpebral conjunctiva is prepared by scissors from the anterior surface of the nictitating membrane to line the posterior surface of the skin, muscle, and tarsus graft already in position (Fig. 5.11b). The base of the graft is lateral, and it should be 1–2 mm wider and longer than its bed. Once adequately separated from the anterior surface of the nictitans, the conjunctival graft is rotated 180 and apposed to the posterior surface of the lid graft by 6-0 simple interrupted absorbable sutures (Fig. 5.11c). The donor area on the anterior surface of the nictitans is left to heal by secondary intention.

removal and graft establishment. Warm and cold compresses may be administered daily to reduce swelling and promote local circulation. The most frequent short-term complication after both of these procedures is postoperative swelling (Fig. 5.12). The most frequent long-term complication after these techniques is the development of a mild cicatricial entropion along the leading margin of the new pedicle graft. The technique by Dziezyc and Millichamp attempts to address this potential complication before its development. An adequate conjunctival lining on the posterior surface of the pedicle graft seems to be the main method to prevent this complication. If trichiasis from the pedicle graft occurs, superficial keratitis at this site may develop. Surgical treatment consists of a focal oval excision of the eyelid skin and orbicularis oculi muscle in the affected area, and eversion of the surgical lid margin.

Postoperative management and complications of myocutaneous pedicle grafts

Distichiasis, or the presence of one or more extra cilia or eyelashes, is a common condition in dogs but rare in cats and other animal species. The cilia emerge from near or within the orifices of the meibomian or tarsal glands (Fig. 5.13). Distichiasis in dogs may be inherited in many breeds, but may also result from metaplasia of the tarsal

Topical and systemic antibiotics are administered after these procedures. An E-collar should be used for the entire postoperative period, and maintained on the patient until suture

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Fig. 5.12 Eight week postoperative appearance of the Roberts–Bistner method for bilateral dorsolateral lid agenesis in a cat. (a) Appearance of face and myopedicle grafts. (b) Close-up appearance of the right eye.

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Surgical procedures for distichiasis

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Fig. 5.13 Positions in the upper eyelid of the dog for normal eyelashes or cilia (A), distichia (B), and ectopic cilia (C).

glands in older animals and from chronic inflammation. Breeds commonly affected with distichiasis include the American Cocker Spaniel, English Cocker Spaniel, English Bulldog, Toy and Miniature Poodles, Boxer, St Bernard, Golden Retriever, Long-haired Miniature Dachshund, Alsatian, Bedlington Terrier, Shetland Sheepdog, Yorkshire Terrier, and the Pekingese. Over 90% of American Cocker Spaniels have distichia; however, treatment for distichiaassociated ophthalmic problems is necessary in only 10% or less of affected dogs. The clinical signs related to distichia are those of irritation, including increased lacrimation, epiphora, blepharospasm, eyelid swelling, conjunctival hyperemia, and corneal disease (vascularization, pigmentation, and/or ulceration). The distichia are fine, the same color as the adjacent hair coat, and best detected by adequate illumination and magnification, and with topical fluorescein stain (Fig. 5.14). Treatment for canine distichiasis consists of either temporary removal of the offending distichia by manual epilation, or the permanent destruction of the distichia follicle by

Fig. 5.14 Distichia coated with mucus emerging from the orifices of the glands of Meibom. Adequate illumination and magnification facilitate their detection.

electroepilation, cryoepilation, and various surgical procedures. The Hotz–Celsus entropion procedures may be used to evert the eyelid margin sufficiently to displace the distichia from touching the conjunctiva or cornea, or both. With the advent of the operating microscope, surgical techniques to remove the distichia follicles and conserve as much as possible of the deeper aspects of the eyelid margin have evolved. Manual epilation of distichia can immediately eliminate the clinical signs associated with these irritating aberrant lashes, but regrowth occurs. Epilation may be used to confirm the clinical signs are secondary to certain distichia, but is usually impractical long term and when multiple distichia are involved. In electrolysis, a fine electrode is inserted into the distichia follicle and 3–5 mA current is used to destroy the follicle germinal cells. Several portable and battery-powered units are available commercially, though current exceeding 5 mA should not be used as excessive electrolysis creates scar tissue formation at the eyelid margin (Fig. 5.15). To adequately perform electrolysis for distichia, general anesthesia is indicated. Magnification and good illumination can help observe the distichia as well as assist the electrolysis. Electrolysis may be selected for treatment of a few distichia but should be avoided when most of the eyelid margin is affected. Electrolysis is of limited success when multiple (compound) distichia exit from a single orifice. Once adequate current is applied, hydrogen gas bubbles occur, and the distichia is easily detached from its base. Low milliamperage is recommended (about 2–3 mA) for 15–30 s. Surgical procedures to excise the distichia follicles have been refined from the initial report of eyelid splitting and excision of the inner margin of the palpebral conjunctiva, to partial tarsal plate excision, and more recently conjunctival resection with minimal disturbance of the lid margin. In humans where distichiasis is infrequent, surgical procedures have been developed to excise the distichia and follicles.

Fig. 5.15 A small battery-powered electroepilation unit may be used to treat limited numbers of distichia.

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Fig. 5.16 For limited numbers of distichia. (a) Resection of the deeper aspects of the lid margin with the tarsoconjunctiva and distichia with the Beaver No. 6500 or 6700 microsurgical blade is performed. The lid margin is stabilized by a chalazion clamp, and the resection of the distichia follicles is limited to only focal parts of the entire eyelid length. (b) A block of tarsoconjunctiva with distichia is excised with small tenotomy scissors at a depth of 4–5 mm. The surgical site(s) should not exceed 5–7 mm long, and three sites per eyelid.

These methods usually divide or split the entire eyelid skin and orbicularis oculi muscle from the tarsus and palpebral conjunctiva from the distichia follicle excision site to the conjunctival fornix. The adjacent tarsus and palpebral conjunctiva are then slid to cover the surgical defect at the eyelid margin. Resection of the distichia follicles and adjacent palpebral conjunctiva is recommended for isolated distichia of the upper and lower eyelid, but should not be used for distichia affecting large portions of the lid margin. The affected eyelid is grasped with a medium to large chalazion clamp to stabilize the lid as well as provide hemostasis. With the Beaver No. 6500 microsurgical blade, the distichia follicle is excised to a depth of 4–5 mm from the eyelid margin (Fig. 5.16a). Once this block of tissue is isolated, small tenotomy scissors are used to excise its base (Fig. 5.16b). The wound is allowed to heal by secondary intention. In the partial tarsal plate excision method, the eyelid is stabilized by a chalazion or entropion clamp. The distichia and follicles are excised by a V-shaped incision on the outer and deeper aspects of the extra eyelashes (Fig. 5.17).

Fig. 5.17 To treat a limited number of distichia in the dog, the distichia may be excised with only part of the tarsal plate to reduce the loss of the eyelid margin tissue. The surgery is limited to those distichia causing eye disease and should not involve the entire eyelid margin. The V-shaped incisions are performed 4–5 mm deep, and the block of eyelid with the distichia follicles excised. During this procedure the eyelid should be stabilized by a chalazion or some other type of clamp.

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Fig. 5.18 Conjunctival resection technique for the treatment of generalized canine distichiasis. (a) The affected area of the eyelid is grasped by the chalazion clamp. The tarsus and palpebral conjunctiva are incised 1 mm and 3–4 mm posterior to the eyelid margin. The block of tarsoconjunctiva and distichia follicles is carefully excised by small tenotomy scissors. Like the previous two methods, the surgery is limited to the offending distichia and should not involve the entire eyelid margin. (b) The surgical defect is allowed to heal by secondary intention.

The incision should be 4–5 mm deep to ensure adequate removal of the distichia follicles. The surgical area is not sutured and allowed to heal by secondary intention. In the conjunctival resection technique, the eyelid is stabilized by a chalazion or entropion clamp. The tarsus and palpebral conjunctiva are incised 1 mm below the eyelid margin in the area of the distichia follicles (Fig. 5.18a). After a second parallel incision, 3–4 mm deep to the first incision, the strip of palpebral conjunctiva, tarsus, and the distichia follicles is excised (Fig. 5.18b). The palpebral conjunctival defect is allowed to heal by secondary intention. Although this method is more tedious than the other methods, it avoids the eyelid margin. More recent investigations have demonstrated the improved benefits of non-invasive cryotherapy for the treatment of canine distichiasis with limited complications. The technique avoids surgery, but necessitates a nitrous (N2O) cryounit. A double freeze–thaw cycle sufficient to produce –25 C with N2O can destroy the distichia follicles without the destruction of the adjacent eyelid margin. The eyelid is grasped and held during cryotherapy by a chalazion or entropion clamp. The cryotherapy procedure should not contact the cornea. As the amount to cryotherapy may vary with each unit, a line pressure of 625 mmHg for the cryoprobe provides for a standard cryofreeze. The cryoprobe is placed on the palpebral conjunctiva directly over the distichia follicles, about 2 mm below the eyelid margin (Fig. 5.19). A glaucoma cryoprobe may freeze about a 4 mm diameter of eyelid tissue. The first freeze of 45 s results in an iceball that advances to about 1 mm anterior to the meibomian gland orifices. After a brief thaw, a second freeze of 25 s is performed.

Postoperative management and complications after distichia surgery Topical treatment with antibiotics and corticosteroids postoperatively minimizes eyelid swelling and reduces the scarring of the eyelid margin that may contribute to occasional

Non-surgical treatment of entropion

Fig. 5.19 (a) For effective cryotherapy of canine distichiasis, a double freeze-thaw cycle is used to destroy the distichia follicles. (b) Immediate appearance after the cryoprobe has been withdrawn to inspect the tissue freeze. Extensive postcryotherapy eyelid swelling should be anticipated, and corticosteroids and non-steroidal antiinflammatory agents should be used perioperatively.

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entropion. After all of the distichia techniques, distichia regrowth (about 10–30%) from inadequate excision of the distichia follicles, eyelid margin fibrosis, focal depigmentation of the postoperative eyelid margin (especially after cryotherapy), and entropion are occasional complications. Surgical procedures for post-distichia treatment entropion may be used to evert the eyelid margin to a relatively normal position. Complications after cryotherapy for distichia include immediate and sometimes excessive eyelid and conjunctival swelling that lasts about 48 h, depigmentation of the eyelid and lid margin within 72 h that usually completely re-pigments within 6 months, and occasional distichia regrowth. Properly performed, eyelid margin scarring and distortion are unlikely after cryotherapy with temperatures that do not fall below –25 C. Eyelid temperatures lower than –30 C have been associated with lid scarring, necrosis, and permanent pigment loss, but not increased efficacy. Topical antibiotics/corticosteroids are necessary perioperatively to decrease the not infrequent marked eyelid swelling and chemosis as rapidly as possible. Preoperative flunixin meglumine (0.1–0.5 mg/kg IV) helps reduce the immediate lid swelling and may need to be continued for the next 48–72 h.

Surgical procedures for ectopic cilia Ectopic cilia primarily affect the upper eyelid of dogs, and are associated with intense blepharospasm, ptosis, epiphora, and a dorsal paracentral or peripheral corneal ulcer (Fig. 5.20). The onset of clinical signs is usually acute. Any breed can be affected, and most animals are young. There is also a direct association of ectopic cilia and distichia in the dog. Upon eversion of the upper eyelid, a single or, more often, multiple cilia emerge from the central palpebral conjunctiva about 4–6 mm from the eyelid margin. The ectopic cilia appear to arise from the base of the tarsal or meibomian glands, or from the base of hair follicles from the overlying eyelid skin. After eversion of the affected eyelid by a chalazion or entropion clamp, the follicle of the ectopic cilia is excised ‘en bloc’ with a scalpel blade, skin biopsy punch, or destroyed by electrocautery or cryotherapy.

Fig. 5.20 Ectopic cilia of the central palpebral conjunctiva. The ectopic cilia follicle is excised ‘en bloc’ or destroyed by cryotherapy or electrocautery. (Photograph courtesy of the late Paul A Dice, Seattle, WA.)

SURGICAL PROCEDURES FOR ENTROPION IN SMALL ANIMALS Entropion or the inversion of the eyelid margin can be divided into three categories: congenital/developmental, spastic, and cicatricial. Developmental entropion is a common condition in purebred dogs and not infrequent in cats. Predisposition occurs in the Chow Chow, Norwegian Elkhound, Chinese Shar Pei, St Bernard, English Springer Spaniel, English and American Cocker Spaniels, English Bulldog, Toy and Miniature Poodles, Great Dane, Rottweiler, and the Bull Mastiff (Fig. 5.21). Often each breed has specific affected areas of the eyelids that are commonly involved. Adjacent areas, such as the nasal folds and redundant facial folds of skin, can compound entropion in certain breeds. Spastic entropion is infrequent in dogs, but the pain associated with the trichiasis from developmental entropion often worsens the basic lid defect.

Non-surgical treatment of entropion Several non-surgical methods to treat entropion in small animals have been used. Subcutaneous injections of antibiotics, paraffin, and mineral oil have been used to provide

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Fig. 5.21 Bilateral upper and lower eyelid entropion in a young English Bulldog. With the associated trichiasis, blepharospasm has developed.

temporary eyelid margin eversion, and relief from the trichiasis and blepharospasm, but generally have been replaced by the different lid surgeries: the larger the volume of injection, the greater the extent of eversion of the eyelid margin. Electrocautery of the skin and superficial aspects of the orbicularis oculi muscle may be used to stimulate the formation of scar tissue and correction of the entropion. The predictability of postcautery fibrosis is low. As a result, several surgical procedures have been developed that provide reasonably consistent and beneficial results. Because of economics and the frequency of congenital entropion in sheep, injections to reverse lower lid entropion are not infrequent.

Fig. 5.22 Entropion in an 8-week-old Chinese Shar Pei puppy. The entropion affects about 300 of the eyelids and the lateral canthus, and resulted in bilateral corneal ulceration.

Temporary eversion – ‘tacking’ Entropion generally requires surgical correction. However, in certain breeds, the eyelid defect may be minor, but becomes extensive with secondary blepharospasm. In the Chinese Shar Pei puppy with entropion, secondary blepharospasm can markedly increase the extent of the original entropion (Fig. 5.22). The redundant facial folds can also contribute to the entropion when blepharospasm is present. Early treatment of the Chinese Shar Pei puppy with entropion, often at the age of 2–4 weeks, with temporary sutures to maintain the eyelid margin in a relatively normal position for 10–20 days, may effectively resolve the condition. Overcorrection with the tacking procedure generally provides better results than undercorrection. Usually two tacking sutures are placed at 45 in the upper eyelid, and, if necessary, in the lower eyelid. Sutures (Lembert type) or skin staples can be inserted to temporarily evert the eyelid margins. Two to three 3-0 to 5-0 non-absorbable interrupted vertical mattress sutures are placed in the upper and infrequently the lower eyelids, about 2–3 mm from the margin, and the second 10–20 mm from the margin (Fig. 5.23) near the orbital rim. The ‘bites’ are fairly large, about 4–5 mm long, to ensure that adequate tension and tissue-holding occur. As the sutures are tightened, the inversion of the eyelid margins is corrected. Often the sutures are left long to permit multiple adjustments. Most Chinese Shar Pei puppies respond to the tacking method. Those puppies that are not improved by the

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Fig. 5.23 Temporary eversion of entropion in very young Chinese Shar Pei puppies may avoid surgical correction later. At least two interrupted vertical mattress sutures are placed in each lid near the eyelid margin and 10–20 mm from the eyelid margins to temporarily correct the lid defects. These sutures are maintained for 10–20 days.

temporary tacking methods develop corneal disease and require entropion surgery. These tacking procedures have also been used in adult dogs to treat spastic entropion, which does not respond to medical and other surgical therapies. By preventing the secondary pain caused by the trichiasis touching the conjunctival and corneal surfaces, the tacking procedure may successfully stop the persistent blepharospasm. These same techniques are useful in lambs.

Quickert–Rathbun procedure Williams recently modified the Quickert–Rathbun technique for young and older dogs with lower lid entropion. In this procedure traction is placed from the lower conjunctival fornix by sutures extending from the fornix to the

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Fig. 5.24 In the Quikert–Rathbun procedure, the distal lower eyelid and margin are rotated outward, using a suture based in the deep conjunctival fornix. (a) A double-ended absorbable suture is carefully positioned in the deep conjunctival fornix. (b) These two sutures are inserted in the skin 1–2 mm from the lid margin and carefully tightened to evert the lid margin.

external skin of the eyelid margin. A double-ended 4-0 absorbable suture is positioned from the deep conjunctival fornix to exit on the lid skin 1–2 mm from the lid margin, which immediately everts the lid margin and corrects the entropion (Fig. 5.24). Tension on the sutures as well as their exit position on the lid surface can be varied to effect entropion correction.

Surgical management of entropion The surgical procedures for the treatment of entropion in animals evolved partially from those techniques reported in humans. In the Celsus procedure (cited by Zeis E 1839 Handbuch der plastischen Chirurgie. G. Reimer, Berlin, p 12) a crescentic area of eyelid skin and orbicularis oculi muscle is removed. In the Celsus–Hotz technique (Hotz CC 1879 Operation for entropion. Archives of Ophthalmology 3:249) the apposition of the surgical wound involved placement of the sutures through the tarsus and orbicularis oculi muscles. Adaptation of the Celsus–Hotz technique has resulted in a most useful procedure that can be varied markedly for a number of different forms of entropion in the canine and feline patient. In Veterinary and Comparative Ophthalmology by Eugene Nicolas and translated by Henry Gray (H. and W. Brown, London, 1914), at least three different surgical procedures were described for entropion in animals. Excision of an oval portion of skin involving the lateral lower eyelid and lateral canthus for the treatment of entropion was referred to as the Berlin–Me´gnin method. A simple method to repair entropion in the dog was reported by Veenendaal (1936). Excision of an arrowhead-shaped section of lateral canthal skin for the treatment of entropion has been referred to as the Schleich method. Fro¨hner’s method consisted of the excision of a somewhat circular section of skin to effect correction of entropion.

Hotz–Celsus procedure for entropion The Hotz–Celsus or Celsus–Hotz procedure and its modifications are the basic surgical techniques for the treatment of congenital, developmental, cicatricial, and senile entropion in domestic animals. The key to its success is the need for the procedure to be performed as close as possible to the

eyelid margin, and the positioning of the maximum aspects of the surgical wound to the area of the most extensive entropion. Because animals lack the tarsal plate, the eyelids lack rigidity and require contact with the globe. The presence of enophthalmia complicates the successful repair of entropion because of the lack of lower lid contact with the globe. The lack of a well-developed lateral canthal ligament in many animal species may also account for the frequent involvement of entropion in this area. Entropion sufficient to produce other ophthalmic diseases, including conjunctivitis, keratitis, and epiphora with dermatitis, should be corrected by surgery. The Hotz–Celsus procedure with its different modifications and several other related techniques effectively treats the majority of the different types of entropion in small animals. The Hotz–Celsus technique can be used to correct entropion of the entire lower lid, the upper eyelid, and, with modification, the lateral canthus. For central lower entropion defects, the following procedure is illustrated. A section of lid skin and orbicularis oculi muscle is excised in this procedure. The length and shape of the skin–orbicularis oculi incisions vary, depending on the amount and area of entropion correction. The initial skin incision is parallel to the eyelid margin, usually 1–2 mm from the lid margin and where the pigmentation of the skin ceases and the eyelid hair begins (Fig. 5.25a). The lid may be held by an entropion clamp or held taut and the eye protected by a Jaeger eyelid plate. The depth of the skin incision can include variable amounts of the orbicularis oculi muscle, and is deeper especially in the large and giant breeds of dogs. The primary goal of the procedure is to evert the eyelid margin and stop secondary blepharospasm. The amount of surgical correction should allow for 0.5–1.0 mm of additional eversion of the eyelid margins that occurs during postoperative healing. The ends of the initial skin–orbicularis oculi incision are joined with a ventral elliptical incision, the width determined by the amount of tissue that needs to be excised to evert the eyelid margin into a normal position (Fig. 5.25b). If the lower entropion involves the medial and lateral one-third of the lid, but not the central section, two separate procedures are performed. To stabilize the eyelid during these incisions, a thumb forceps may also be inserted at the lateral canthus to provide tension on the lids. The area of skin may also be outlined and slightly crushed by curved mosquito forceps. This technique is more traumatic, but provides some hemostasis. Hemorrhage is usually minor and occurs from the lateral and medial ends of the incisions. Temporary clamping of the larger blood vessels by hemostats or digital pressure is usually sufficient. Ligature of these bleeders is not usually necessary, and the buried suture material may cause local fibrosis of the lid. The incised area of eyelid skin and orbicularis oculi muscle is elevated by thumb forceps and excised by small curved Steven’s tenotomy scissors. The surgical wound is apposed with 4-0 to 6-0 simple interrupted non-absorbable sutures placed about 2–3 mm apart (Fig. 5.25c). Placement of the sutures must accommodate the shorter eyelid margin wound and the longer distal incision (Fig. 5.25d). Suture placement starting from the central defect and working in each direction, as well as wound apposition starting from one end, may be used.

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Fig. 5.25 Modified Hotz–Celsus technique for central lower lid entropion. (a) The skin and orbicularis oculi muscle layers are incised by scalpel. The incision along the eyelid margin should be 1–2 mm from the margin. The lower incision is determined by the length and shape of the entropion. (b) The strip of eyelid skin and orbicularis oculi muscle are carefully dissected and excised by small tenotomy scissors. (c) The surgical wound is apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures. The sutures should be angled somewhat to accommodate the two different lengths of the wound edges. (d) At the conclusion of surgery because of the eyelid swelling, slight overcorrection may be present. (e) Preoperative appearance of a cat with bilateral lower lid medial entropion (right eye shown). (f) Same cat immediately after bilateral Hotz–Celsus procedure (left eye shown).

Modification of Hotz–Celsus technique for medial entropion The Hotz–Celsus procedure may be modified for medial entropion and epiphora in miniature breeds of dogs. The objective of this technique is to evert the medial lower eyelid margin sufficient to assist the lower lacrimal punctum to conduct tears to its orifice (Fig. 5.26). The extent of the lower eyelid skin–orbicularis oculi muscle to be excised is determined preoperatively by estimating the number of millimeters of correction necessary to evert the medial lower eyelid. The incision should not be deeper than the orbicularis oculi muscle to avoid damage to the lower lacrimal punctum and canaliculus.

Bigelbach modification for medial entropion Bigelbach has modified the medial entropion procedure by the excision of a 2–3 mm strip of the upper and lower eyelids at the medial canthus, after the identification of both lacrimal punta. In addition, the caruncle is excised, resulting in an ‘anchor-shaped’ defect. The areas are not apposed by sutures and allowed to heal by secondary intention. The resultant healing effectively treats the medial upper and lower entropion.

Modification of the Hotz–Celsus method for lateral canthal entropion The Hotz–Celsus procedure may be adapted for entropion of the lateral one-third of the upper and lower eyelids, and the lateral canthus. This modification is recommended when the palpebral fissure size is normal, and an additional enlargement of the palpebral fissure is not necessary. If the lateral canthal entropion is associated with a micropalpebral fissure (or the eyelids are shorter than normal), the arrowhead and other surgical procedures are indicated. The procedure is similar to the methods described previously, but adapted to provide eversion of the outer one-third of both the upper and lower eyelids (Fig. 5.27).

‘Y’ to ‘V’ plasty for entropion

Fig. 5.26 The Hotz–Celsus technique may be modified to treat medial entropion and secondary epiphora in miniature breeds of dogs. The tip of the triangle of the wound is opposite the lower lacrimal punctum and designed to improve lower punctum function.

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The ‘Y’ to ‘V’ plasty for entropion successfully corrects mild central entropion of the upper and lower eyelids. This procedure can also be reversed: ‘V’ to ‘Y’ or the Wharton–Jones blepharoplasty for the correction of mild central cicatricial ectropion. The initial Y incision, starting about 1 mm from the eyelid margin, is sufficiently deep to include the eyelid

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Fig. 5.27 The Hotz–Celsus method can be modified for lateral entropion of the upper and lower eyelids. The correction does not affect the size of the palpebral fissure.

skin and orbicularis oculi layers (Fig. 5.28a). The length of the basal part of the Y incision is designed to provide the appropriate amount of correction for the entropion. The triangular flap of skin is elevated, and its base separated from the underlying tarsus by blunt–sharp dissection with small tenotomy scissors (Fig. 5.28b). The tip of the skin–muscle flap is apposed to the bottom and sides of the skin–muscle layers with 4-0 to 6-0 simple interrupted non-absorbable sutures, resulting in a V-shaped closure (Fig. 5.28c).

Central tarsal pedicle for entropion (Wyman) The central tarsal pedicle has been combined with the Hotz– Celsus procedure to treat central lower entropion. The technique involves construction of a pedicle of tarsus to evert the eyelid margin. This pedicle is secured in the subcutaneous tissues. The procedure has been used for congenital and developmental entropion in the Chow Chow, Chinese Shar Pei, English Bulldog, and Rottweiler. It has also been employed for recurrent entropion in dogs and cats treated previously by surgery. This procedure is recommended for severe and recurrent entropion in small animals. The traditional Hotz–Celsus technique is performed first, but the surgical procedure does not extend as deep as the orbicularis oculi muscle (Fig. 5.29a). The distal elliptical skin incision is performed after the tarsal pedicle has been completed. Two parallel incisions are made through the orbicularis oculi muscle and tarsus immediately below the

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area of the most extensive entropion. The tarsal pedicle is constructed by scalpel dissection with its base at the eyelid margin (Fig. 5.29b). It is then freed from the deeper palpebral conjunctiva and more superficial skin. A subcutaneous tunnel, that is as wide as the pedicle, is prepared by tenotomy scissors in the lower incision to correct the entropion: the more severe the entropion, the longer the subcutaneous tunnel. With a double-armed 5-0 non-absorbable suture, a cruciate stitch is placed in the tarsal pedicle and extended through the subcutaneous tunnel to be tied at the level of the skin with a stent (Fig. 5.29c). As the suture is tightened and tied, the entropion area should be corrected. The distal elliptical section of skin is now excised by tenotomy scissors (Fig. 5.29d). Apposition of the skin wound is by 4-0 to 5-0 simple interrupted non-absorbable sutures (Fig. 5.29e). Multiple tarsal pedicles can be used when more than one area of the eyelid is affected. The tarsal pedicle technique is often combined with a permanent lateral tarsorrhaphy.

Combined entropion–distichiasis procedure The surgical procedures for entropion and distichiasis may be combined in the dog. The distichia follicles are excised using the tarsoconjunctival resection methods described in an earlier section. The Hotz–Celsus procedure is then performed to correct the entropion. Wound apposition is by 4-0 simple interrupted silk sutures. Each skin suture includes a deep bite of tarsus to assist with eyelid margin eversion.

Stades combined entropion–trichiasis procedure The entropion and trichiasis procedures are combined for breeds of dogs with upper eyelid entropion and large areas of redundant skin on the forehead (Fig. 5.30). Performance of only the entropion procedure, usually the Hotz–Celsus method, may not completely correct the defect as the excess skin above both eyes results in recurrent upper entropion. This procedure and modifications of this method are used in selected breeds including the English Cocker Spaniel, Chow Chow, Chinese Shar Pei, and Bloodhound. At least two different surgical methods have been used to treat the unusual entropion complicated by redundant forehead folds of skin. In the combined upper eyelid

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Fig. 5.28 The ‘Y’ to ‘V’ plasty for entropion may be used for mild entropion of the central portion of the lower lid. (a) The initial ‘Y’ incision of the lid skin and orbicularis oculi muscles layers by Beaver No. 6700 microsurgical blade starts about 1 mm from the eyelid margin. The lower part of the incision will determine the extent of the lid eversion. (b) A triangular section of skin and orbicularis oculi muscle, based at the eyelid margin, is dissected from the underlying tarsus by tenotomy scissors. (c) The tip of the skin–muscle flap is apposed in a ‘V’ shape to effect eversion of the eyelid margin with 4-0 to 60 simple interrupted non-absorbable sutures.

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Fig. 5.29 Central tarsal pedicle for entropion. (a) A tarsal pedicle anchored at the eyelid margin is combined with the Hotz–Celsus procedure. The initial skin incision is performed by the Beaver No. 6700 microsurgical blade about 1–2 mm from the eyelid margin. (b) A tarsal pedicle is constructed by scalpel with its base at the eyelid margin of the most extensive entropion. (c) Through a subcutaneous tunnel made by scissors, a 5-0 non-absorbable cruciate suture attached to the tarsal pedicle is secured with a stent below the surgical wound. (d) The second skin incision of the Hotz–Celsus method is performed, and the section of skin is excised by tenotomy scissors. The width of the surgical wound varies with the extent of the entropion. (e) The skin wound, to correct the remainder of the entropion, is apposed with 4-0 to 5-0 simple interrupted non-absorbable sutures.

Fig. 5.30 The Chinese Shar Pei can benefit from either the Stades procedure or the Hotz–Celsus procedure, combined with resection of variable amounts of forehead skin. These combinations assist greatly when the upper eyelids also have entropion.

trichiasis and entropion procedure, reported by Stades, a section of upper eyelid skin is excised extending vertically 0.5–1.0 mm from the upper eyelid margin to 15–25 mm above the palpebral fissure, and horizontally 2–4 mm medial from the nasal canthus to 5–10 mm external to the lateral canthus (Fig. 5.31a–d). The upper eyelid wound is partially closed by the apposition of the upper eyelid skin to the subcutaneous eyelid layer 5–6 mm from the eyelid

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margin with 4-0 to 5-0 simple interrupted or a combination of simple interrupted and continuous non-absorbable sutures (Fig. 5.31e–g). The exposed area immediately above the upper eyelid margin heals by secondary intention. The resultant fibrosis everts the upper eyelid margin. This area may become pigmented. The animal still retains its facial folds of skin and its overall appearance is not markedly altered. The second procedure consists of two parts: the excision of a large section or facelift of the redundant forehead skin (Fig. 5.32), and the Hotz–Celsus technique (or some modification thereof) to evert the upper eyelid margin and, if indicated, the lateral canthus. The redundant skin in the forehead is excised to an extent that these folds of skin do not affect the eyelids. Two curvilinear skin incisions are performed for the forehead skin resection. The skin is resected by Metzenbaum scissors, and the edges are apposed with 3-0 to 4-0 simple interrupted non-absorbable sutures. The upper entropion, or upper lid and lateral canthal entropion, is corrected by the Hotz–Celsus procedure or modifications.

Modified Hotz–Celsus procedure for entropion and ectropion The Quickert technique for humans has been modified for the dog with a combination of lower entropion and ectropion. After the Hotz–Celsus procedure has been performed, a wedge of eyelid margin is excised from the center of the Hotz–Celsus procedure. The eyelid margin is apposed with a figure-of-eight suture, and the Hotz–Celsus wound apposed with simple interrupted non-absorbable sutures.

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Fig. 5.31 Stades procedure for entropion and redundant forehead folds of skin. (a) A large section of upper eyelid skin will be resected. The skin incisions extend from 0.5–1.0 mm from the eyelid margin to 15–20 mm dorsally. (b) Intraoperative appearance in an English Bulldog. The large skin incision approaches but does not include the upper lid margin. (c) The skin section is excised carefully by tenotomy scissors. The size of the eyelid flap assists correction of the upper eyelid entropion, and compensates for the redundant forehead skinfolds. (d) Intraoperative photograph, showing the extent of the skin removal. (e) Apposition of the surgical wound with 4-0 to 5-0 simple interrupted non-absorbable sutures is incomplete, leaving 5–6 mm of subcutaneous tissue of the upper eyelid to heal by secondary intention and rotate the lid margin outward. (f) Immediate postoperative appearance of the left eye. Note the exposed subcutaneous tissues immediately behind the lid margin. (g) Immediate postoperative appearance of the face after bilateral lid surgeries.

Face lift/skinfold excision and rhytidectomy For many breeds of dogs the excision of periocular (orbital and forehead) skinfolds may be combined with other entropion surgeries, such as the Hotz–Celsus or Stades procedures, to effectively treat upper and lateral canthal entropion. In breeds such as the Chinese Shar Pei, Bloodhound, and some of the spaniel breeds, the skin above the eye and on the forehead may be grasped in the awake patient, and ‘gathered’ until the upper entropion is corrected. Rather large amounts of forehead skin can be safely excised in this method as semicircular areas. The surgical skin defects are apposed with 3-0 to 4-0 simple interrupted sutures.

Surgical procedures for lateral canthal entropion The lateral canthal region of the dog lacks stability because of the absence of a strong and rigid lateral canthal ligament. The lateral retractor anguli oculi muscle partially replaces the function of the lateral palpebral ligament, but the area remains unstable and is a frequent location for entropion. Lateral canthal surgical procedures usually extend variable lengths into the upper and lower eyelids, and not necessarily equally. As a result, each surgical procedure should be modified for the individual lateral canthal defect. At least three surgical procedures concentrate on entropion of the lateral

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Fig. 5.34 The arrowhead procedure for correction of lateral canthal entropion is a further modification of the Hotz–Celsus procedure. The procedure will also slightly increase the size of the palpebral fissure. Fig. 5.32 In certain breeds, like the Chow Chow or the Chinese Shar Pei, treatment of entropion can also include the resection of a large section of forehead skin and the Hotz–Celsus procedure, as shown in this immediate postoperative photograph.

Fig. 5.33 The large and giant breeds of dogs with lateral canthal entropion have lateral canthal instability and often a ‘diamond’-shaped palpebral fissure.

canthus. Two of the three procedures increase the stability of the area by constructing additional lateral canthal support (Fig. 5.33). These three surgical procedures include the arrowhead procedure, lateral canthoplasty by the Wyman technique, and modifications of the Wyman procedure.

Arrowhead procedure for lateral canthal entropion The arrowhead procedure may be used to correct lateral canthal entropion, but does not substantially increase the size of the palpebral fissure. The extent of correction of lower and upper entropion may vary depending on the degree of lid inversion of each eyelid margin. The arrowhead procedure is indicated for lateral canthal entropion with normal-sized palpebral fissures and normal length upper and lower eyelids. A subcutaneous lateral canthal suture may be added to this procedure to anchor and stabilize the lateral canthus, and positioned just before the lid skin is apposed.

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The lateral canthal region is stabilized with a thumb forceps placed in the lateral conjunctival fornix or with the lateral canthus grasped with the Lordan triangular chalazion and/or Desmarres forceps. These forceps also assist with local hemostasis. The technique is similar to the Hotz–Celsus procedure, except for its shape (Fig. 5.34). The skin and orbicularis oculi layers are incised with the Bard–Parker No. 15 blade or Beaver No. 6700 microsurgical blade 1–1.5 mm from the eyelid margin. The width of the surgical site is determined by the size of the original lid defect. The skin and orbicularis oculi layers are carefully excised by tenotomy scissors. If the lateral canthus tension suture is used, it is positioned now. A 4-0 monofilament non-absorbable simple interrupted or horizontal mattress suture is placed at the lateral canthus in the muscle–tarsal layers and then in the fascia overlying the orbital ligament. The suture is gradually tightened to tense the lateral canthus into the desired position. The surgical wound is apposed with 4-0 to 6-0 simple interrupted non-absorbable sutures, with the first suture placed at the lateral canthus.

Lateral canthoplasty by Wyman The lateral canthoplasty procedure, as developed by Wyman, attempts to address the lack of lateral canthal stability and the associated lateral canthal entropion of large and giant breeds of dogs. The breeds of dogs that may benefit from this procedure include the St Bernard, Newfoundland, Chow Chow, Golden Retriever, Bull Mastiff, Rottweiler, and English Bulldog. These large breeds often have some enophthalmia, and the lack of globe support for the lower eyelid may also predispose to entropion. These same breeds may also have a round-, diamond- or pergola-shaped palpebral fissure, and a combination of lateral entropion and central ectropion of both eyelids. With correction of the lateral canthal entropion, a significant portion of the central lower ectropion (or central eversion of the eyelid margin) will also resolve. After draping, an elliptical skin incision is made by scalpel (Fig. 5.35a). The incision should be 1–1.5 mm from the lateral eyelid margins. The width between the two elliptical skin incisions is the amount of correction for the lateral canthal entropion. The orbicularis oculi muscle is exposed with blunt–sharp dissection with small tenotomy scissors. Upper and lower pedicles of orbicularis oculi muscle are constructed by scalpel with their base at the lateral canthus (Fig. 5.35b). The lateral canthus is dissected further to

Postoperative management and complications

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Fig. 5.35 The lateral canthoplasty and construction of a lateral canthal ligament by Wyman has proven useful for large and giant breeds with central ectropion and lateral entropion of both eyelids and the lateral canthus. (a) Two elliptical skin incisions are performed. The width of the surgical wound (6–10 mm) should approximate the amount necessary to effect correction of the entropion. (b) Two myotomies are performed with their base at the lateral canthus. These strips of muscle will form the new lateral canthal ligament. (c) After subcutaneous dissection by tenotomy scissors, the pedicle of orbicularis oculi is secured by a cruciate suture to the periosteum of the zygomatic arch by a 4-0 to 5-0 simple interrupted non-absorbable suture. (d) The skin layers are apposed by 4-0 to 5-0 simple interrupted non-absorbable sutures.

expose the lateral orbital rim and/or zygomatic arch. The two muscle pedicles are united with a 4-0 to 5-0 nonabsorbable cruciate suture, and secured to the periosteum of the zygomatic arch (Fig. 5.35c). The skin layer is apposed with 4-0 to 5-0 simple interrupted non-absorbable sutures (Fig. 5.35d). Because of the additional dissection involved with this method, more postoperative swelling of the lateral canthus usually occurs.

Lateral canthoplasty with suture This surgical procedure is a modification of the Wyman lateral canthoplasty and, instead of the orbicularis oculi muscle pedicle, a non-absorbable suture is used to secure the lateral canthus. This adaptation reduces the time for surgery, and with less tissue dissection the postoperative eyelid and lateral canthal swelling are reduced. An alternative method that we have used replaces the non-absorbable suture with a section of frozen scleral homograft. The eyelid skin and part of the orbicularis oculi muscle are excised to correct the lateral canthal entropion. The exact shape and size of the upper and lower aspects of the elliptical incisions vary, depending on the extent of entropion of the upper and lower lids. Once the skin layer is excised, the dissection is continued laterally by small tenotomy scissors to isolate an area to secure the lateral canthus. A single 2-0 non-absorbable suture (or occasionally two sutures) is secured in the lateral canthus and the periosteum of the zygomatic arch (Fig. 5.36). The tension on the suture can be adjusted to provide a reasonably normal sized and shaped palpebral fissure. The skin layer is apposed with 4-0 to 5-0 simple interrupted non-absorbable sutures.

Robertson’s lateral canthal tendonectomy Robertson has described a procedure to treat lateral canthal entropion that releases the tension in large and giant breeds of dogs by transection of the lateral canthal tendon.

Fig. 5.36 As an alternative to the pedicle of orbicularis oculi muscles in the lateral canthoplasty procedure, one or preferably two sutures or a section of frozen scleral homograft can be used to attach the lateral canthus and the periosteum of the zygomatic arch, and stabilize the lateral canthus.

The lateral canthus is everted by forceps to expose the palpebral conjunctiva. With curved Steven’s or tenotomy scissors, the palpebral conjunctiva is separated from the deeper tarsus in a 9 mm arc. The fibrous band is located by blunt dissection that extends from the lateral canthus to the orbital ligaments and zygomatic arch, and a wedge of the tendon excised near its base. An alternative technique is to sever the tendon (tendonotomy) by scissors midway between its origin and insertion. The conjunctival wound is not apposed by sutures. Other entropion techniques may be combined with this method.

Postoperative management and complications Topical antibiotics/corticosteroids are usually administered after entropion surgery. If corneal ulceration, secondary to the entropion, is present, topical antibiotics and mydriatics are indicated. Systemic antibiotics are infrequently indicated except for the lateral canthoplasty techniques when tissue dissection and surgical time are greater. The E-collar should be used after all of these procedures to prevent self-trauma

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and wound dehiscence. The skin sutures are usually removed at 7–10 days, especially if silk is used. Sutures left too long may cause excessive irritation. Complications after these entropion procedures are usually associated with under- and overcorrection of the defect. Occasionally, another surgical procedure may be necessary to secure a reasonable repair, especially if the surgery is performed in young and growing puppies and kittens. The purpose of these procedures is a cosmetically acceptable and functional eyelid. Completely normal eyelid contour may not always be achieved. If the skin–orbicularis oculi muscle incision is too close to the eyelid margin, the sutures are very difficult to place, and there is a greater possibility of the sutures touching the cornea. If the linear incision along the eyelid margin is too far from the margin, the extent of eversion of the entropion is less. Suture failures are unlikely. Use of the E-collar provides excellent protection against the patient rubbing the surgical site that can result in local lid swelling and premature suture loss. With suture loss and wound dehiscence, there is additional postoperative fibrosis and often overcorrection. If overcorrection of the entropion occurs, the blepharospasm may have been overestimated or excessive tissue was excised. If undercorrection results, usually insufficient tissue was removed. The large and giant breeds of dogs with entropion and enophthalmia present additional challenges because the globe–lower eyelid contact is limited and entropion repair is less predictable. The breeds with excessive forehead skinfolds and heavy ears complicate entropion surgery. They often require concurrent excision of large amounts of forehead skin which will affect the dog’s appearance.

ADAPTATIONS IN LARGE ANIMALS AND SPECIAL SPECIES

Entropion in horses Entropion is an inward rolling of the eyelid, allowing eyelid hair to contact the cornea and conjunctiva. Rubbing and irritation from the hair position result in blepharospasm and increased tearing. Corneal ulcers and keratitis commonly occur. Entropion occurs in young foals and is considered to be hereditary in some cases. However, many episodes of entropion in young foals occur in dehydrated, premature, or septicemic animals, and in such cases acquired entropion seems more likely. Permanent surgical correction, therefore, is not indicated in all cases. Non-surgical management may be corrective in most cases. In acute entropion in foals, lubrication of the cornea and conjunctiva with ophthalmic lubricating ointment (artificial tears, ophthalmic ointment petrolatum, or OptixcareW gel) with manual repositioning may be all that is necessary for a good result and avoidance of surgical correction. The injection of different materials into the lower eyelid will also result in temporary correction of the entropion. The injection of 0.5–1 mL of procaine penicillin G into the eyelid at the base of the entropion and massaged toward the eyelid margin may correct the inrolling for a short period of time.

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The injection of liquid paraffin has been reported, but is not recommended due to the risk of inflammatory reaction. If manual repositioning does not correct the problem in young foals, the use of everting sutures is considered. Sutures are placed in a vertical mattress pattern. To ensure ideal eversion of the eyelid margin and haired skin, the sutures should be placed near the eyelid margin (approximately 2–3 mm from the margin). The suture bite should not be so large as to overcorrect the entropion. If overcorrection occurs, the resulting ectropion may interfere with eyelid closure, and ocular irritation may develop from exposure of tissues. Increased tension on the sutures may cause the sutures to cut through the thin eyelid skin. This will lead to failure of the procedure and increased scar tissue formation. Non-absorbable suture material of 3-0 to 5-0 size is preferred. Sutures are commonly left in place for 7–14 days. Skin staples have been used with variable results. The use of staples may be less stressful on these compromised sick foals. They are readily available and rapid to place in the foal with systemic conditions. Everting the eyelids with sutures or staples will frequently be adequate to achieve correction of the entropion, especially if the cause of the entropion can be corrected.

Permanent correction of entropion in the horse Entropion in older horses is commonly associated with cicatrix formation and requires surgical correction. Entropion associated with localized eyelid disease such as scar formation is corrected using a ‘Y’ to ‘V’ procedure (see Fig. 5.28). Initially a Y incision is made, with the arms of the Y extending slightly (1–2 mm) beyond the lateral and medial extent of the lesion. A flat instrument (e.g., Jaeger eyelid plate, sterile wooden tongue depressor, handle of a surgical scalpel) is inserted behind the eyelid into the conjunctival fornix to stabilize the skin and facilitate the skin incision. Ophthalmic cautery and a No. 15 blade are used. The length of the stem of the Y is determined by the amount of eyelid eversion needed. The skin is dissected from the subcutaneous tissues and undermined, and the existing scar tissue excised. The incision is positioned and sutured in a V-shaped closure, creating eversion of the eyelid margin. The skin is closed in a single layer using 4-0 to 5-0 simple interrupted non-absorbable sutures. In the horse, more generalized and non-cicatricial entropion is corrected using a modified Hotz–Celsus procedure. In this technique, a crescent-shaped or elliptical area of skin and orbicularis oculi muscle is excised (Fig. 5.37). The first incision is made parallel to and near (2–3 mm) the eyelid margin. The amount of skin and orbicularis oculi muscle to be removed is determined in the awake horse by ocular examination. The eyelid is examined, then a blink response or palpebral reflex is induced and the eyelid re-examined. After the examiner is satisfied with this assessment, topical anesthetic (0.5% proparacaine) is applied to the cornea and the eyelid re-examined without the blepharospastic component. The horse is then anesthetized and the surgical site prepared for aseptic surgery. The eyelid skin may be stabilized with a Jaeger eyelid plate, the handle of a surgical scalpel, or a sterile wooden tongue depressor inserted behind the eyelid into the conjunctival fornix. The skin is

Entropion and periocular fat pads in the Vietnamese potbellied pig (Sus scrofa)

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Fig. 5.37 (a) Preoperative appearance of lower lid entropion in a young horse. (b) Postoperative appearance after correction using the Hotz–Celsus surgical procedure.

incised, and the skin and a portion of the orbicularis oculi muscle excised with small surgical scissors (see Fig. 5.25). In many cases about half as much muscle as skin is excised, which leads to good repair for the entropion and a cosmetic result. The skin is closed in a single layer using 4-0 to 5-0 non-absorbable (monofilament nylon) sutures. Sutures are removed in 10–12 days. When entropion is associated with a small eyelid scar, a ‘Y’ to ‘V’ procedure is often the best therapeutic option. The arms of the Y should extend only slightly beyond the extent of the entropion (see Fig. 5.28). The stem and height of the Y are determined by the amount of eyelid eversion needed. The adjacent skin is undermined and the scar tissue excised from normal tissue. The skin is apposed with 4-0 to 5-0 non-absorbable (monofilament nylon) sutures in a simple interrupted pattern. Sutures are removed in 10–12 days.

Aftercare following entropion surgery in the horse Preoperative topical and systemic antibiotics are indicated. The placement of a subpalpebral lavage system will facilitate topical application of solutions to the eye. Postoperative swelling can be reduced by the administration of systemic non-steroidal anti-inflammatory agents (flunixin meglumine 1 mg/kg IV) immediately before surgery. Postoperative edema will be lessened by the application of ice packs for the first 24 h after surgery. If swelling

is present 24 h after surgery, warm compresses may further reduce the swelling and discomfort at the surgical site. As rubbing or self-mutilation is often a concern in the horse, the surgical site or eye must be protected by a protective hood with a plastic or solid eyecup (EyeSaver™, Jorgensen Laboratories, Loveland, CO.). Skin sutures are usually removed 8–12 days after surgery. In situations when tension on the suture line cannot be avoided, sutures are left in place for 18–24 days.

Entropion in sheep Entropion or inversion of the eyelid margins may be fairly common in newborn lambs in some flocks (Fig. 5.38). Financial constraints and the need to treat several lambs in the same flock have led to some interesting forms of therapy. The Hotz–Celsus entropion procedure is also successful in lambs but often cost-prohibitive. Entropion may be corrected by subcutaneous injections in the eyelid skin using procaine penicillin, mineral oil, water, air, and warm beeswax. The amount varies, but 1–2 mL is usually adequate. As the agent is injected, the lid is rotated outward and away from the eye. Another rapid form of correction is office staples and surgical staples to evert the lid margin. Excision of lid skin and muscle followed by a single absorbable suture has also been reported.

Entropion and periocular fat pads in the Vietnamese potbellied pig (Sus scrofa)

Fig. 5.38 Lower lid entropion in a lamb with secondary corneal disease. There are several surgical and non-surgical avenues for repair.

Vietnamese potbellied pigs are predisposed to entropion, relative enophthalmia, large periocular fat pads, predisposition to obesity, and heavy forehead brows and upper eyelids. The upper entropion may induce corneal ulceration, but more often corneal vascularization and scarring. Often with increased age, these interrelated factors eventually decrease vision and produce behavioral changes (apprehension, aggression, poor socialization, and fear biting). Surgery for entropion in this species includes: 1) resection of the fat pads beneath the eyelids; 2) the Hotz–Celsus procedure for entropion, often with overcorrection; 3) resection of part of the large (and heavy) forehead; and 4) postoperative control of diet to reduce the obesity long term. This surgical procedure is similar to that in the large breeds of dogs

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C D Fig. 5.39 Bilateral entropion in a Vietnamese pot-bellied pig. Surgical considerations include correction of the entropion (often 360 ), removal of fat pads within the affected eyelids, and removal of the excessive forehead brows. (a) Preoperative appearance of an affected pig. Note the generalized obesity. (b) Intraoperative photograph. Often over-correction of the entropion is performed to compensate for the obesity. (c) Examples of the large sections of forehead brows removed to reduce pressure on the upper eyelids. (d) Postoperative appearance at surgery. Long-term diet management is essential to prevent return of the entropion.

for forehead resections and entropion procedures, but is complicated by the need to also resect the large and often extensive subcutaneous fatty tissues (Fig. 5.39). The surgery is performed under general anesthesia; premedication includes midazolam (0.3 mg/kg IM) and butorphanol (0.3 mg/kg IM). Isoflurane anesthesia is induced by mask, then the animal intubated and maintained on isoflurane and oxygen. The entire face and forehead are prepared for surgery by clipping the hair and disinfection of the skin by dilute povidone–iodine (0.5%) solution. Correction of the upper entropion may be combined with resection of a large forehead section of skin. When combined with forehead skin resection and upper entropion correction, the skin incision starts just ventral and rostral of the tragus of one ear and continues rostromedially along the ventral aspect of the fat pad to the lateral canthus, and then to within 2–3 mm from the upper lid margin; the skin incision is then continued on the opposite side of the face. Both forehead and upper eyelid skin and fat pads are excised. Any facial muscle is spared, but fatty tissues are excised by sharp dissection, and the large forehead section and upper eyelids excised. After absorbable 2-0 subdermal sutures to close potential dead space, the leading edge of the remaining forehead skin is carefully apposed to the surrounding skin and upper eyelids with simple interrupted non-absorbable sutures. For lower lid entropion, the Hotz–Celsus procedure is used (usually an overcorrection), and the excessive fatty tissues also removed.

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Postoperative medications for several days may include: 1) ceftiofur (3 mg/kg PO or IM) for antibiosis; 2) flunixin meglumine (0.7 mg/kg PO or IM) for postoperative swelling; and 3) butorphanol (0.1–0.17 mg/kg IM q8h) for pain.

SURGICAL PROCEDURES FOR ECTROPION Ectropion or the eversion of the eyelid is less dangerous to the eye, but can produce chronic keratitis, conjunctivitis, keratoconjunctivitis, epiphora, and tear staining of the eyelids (Fig. 5.40). Of the animal species with ectropion, dogs (particularly the large breeds) are most frequently affected. Ectropion may be associated with developmental, cicatricial, traumatic, neurologic, and postoperative causes. The breeds of dogs frequently affected with lower lid ectropion include the Bloodhound, St Bernard, Great Dane, Newfoundland, Mastiff, and many spaniel breeds. In some breeds both the eyelids and palpebral fissure are excessive in size and length. In some large and giant breeds of dogs the laxity of the lower eyelid may vary with the fitness and the age of the animal. Central ectropion may also be associated with lateral canthal entropion. Part of the ophthalmic pathology secondary to ectropion is associated with impaired blink reflex, preocular film defects, and impaired tear movement to the medial conjunctival sac. Surgical correction of ectropion is recommended when secondary ophthalmic disease results and requires

Surgical procedures for ectropion

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Fig. 5.41 Lateral eyelid wedge excision procedure. (a) A full-thickness triangular section of lower lid is excised by scissors. A thumb forceps is inserted at the lateral canthus to provide tension on the lower lid. (b) The surgical defect is apposed by two layers of sutures. The tarsoconjunctival layers are apposed with a 3-0 to 5-0 simple continuous absorbable suture. The skin–muscle layers are apposed with 4-0 to 5-0 simple interrupted non-absorbable sutures. Fig. 5.40 Ectropion can produce chronic ocular irritation, such as conjunctivitis. Ectropion surgical procedures generally shorten the length of the eyelid.

long-term topical medications to control the local inflammation and irritation. Surgery should attempt to provide a relatively normal length lower eyelid. Overcorrection should be avoided as entropion may result and can cause potentially more damage to the cornea and conjunctiva. The different ectropion surgical procedures for the lower eyelid primarily shorten and strengthen the lid. As the medial canthus is relatively fixed and more complicated by the presence of the nasolacrimal apparatus and the nictitating membrane, most ectropion surgical procedures involve the lateral one-half of the lower eyelid and the lateral canthus. Procedures for the correction of ectropion include simple triangle excision at the lateral canthus, ‘V to Y’ plasty for cicatricial ectropion, the Kuhnt–Szymanowski procedure, the Kuhnt–Helmbold procedure, and the Munger and Carter modification of the Kuhnt–Helmbold technique.

Lateral eyelid wedge excision In this procedure, the lower eyelid is shortened by the excision of a full-thickness wedge or triangular section of lid. The lid excision is performed at the lateral canthus to avoid the development of an unsightly postoperative eyelid margin notch that may occur when this surgery is performed elsewhere. The size of the wedge of lower lid to be

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removed should be slightly smaller than the extent of eyelid shortening and correction anticipated. As with entropion procedures, postoperative fibrosis generally provides an additional 0.5–1 mm correction. The surgery is performed immediately next to the lateral canthus. A triangular full-thickness section of lower eyelid is excised by strabismus scissors or small Metzenbaum scissors (Fig. 5.41a). The eyelid may be stabilized by a chalazion or entropion forceps, or the entire lower eyelids may be tensed by a thumb forceps positioned in the lateral canthus. The surgical wound is apposed by two layers of sutures (Fig. 5.41b). In the deep layer, a 3-0 to 5-0 simple continuous absorbable suture is positioned in the submucosa of the palpebral conjunctiva and tarsus. The knots are buried to prevent contact with the cornea. Starting at the eyelid margin, the superficial layer of eyelid skin and orbicularis oculi muscle is apposed with 4-0 to 5-0 simple interrupted non-absorbable sutures.

‘V’ to Y’ plasty (Wharton–Jones procedure) The ‘V’ to ‘Y’ plasty is the reverse of the surgical procedure used for cicatricial entropion. Unless a section of the eyelid margin is excised, the ‘V’ to ‘Y’ plasty tightens but not substantially shortens a lower eyelid with ectropion. Starting about 1 mm from the lower eyelid margin, two converging skin incisions are performed on each side of the scarred area (Fig. 5.42a). The V-shaped skin flap is retracted upward, and the scar tissue in the subcutaneous layer and, if present, in the tarsal layer is excised by

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Fig. 5.42 The ‘V’ to ‘Y’ plasty may be used to treat mild cicatricial ectropion. (a) Converging skin incisions are performed by the Beaver No. 6700 microsurgical blade starting 1 mm from the eyelid margin. (b) The ‘V’ shaped skin flap is separated from the subcutaneous tissues, and the scar tissue excised. (c) The skin flap is apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures as a ‘Y’ shaped closure.

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Fig. 5.43 The Kuhnt–Szymanowski procedure is used to correct ectropion and shorten the length of the lower lid. (a) The lower eyelid is split at the ‘gray line’ of the eyelid margin at a depth of 10–15 mm and the incision is extended beyond the lateral canthus. (b) The skin–muscle flap is separated by blunt dissection using tenotomy scissors. (c) Wedges of equal size of tarsoconjunctiva, orbicularis oculi muscle and skin are excised by tenotomy scissors. (d) The tarsoconjunctival defect is apposed by 4-0 to 6-0 simple interrupted absorbable sutures with the knots buried to avoid corneal contact. The skin wound is apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures. The eyelid margin is apposed by 5-0 to 6-0 through-and-though interrupted mattress non-absorbable sutures.

tenotomy scissors (Fig. 5.42b). The adjacent subcutaneous tissues are undermined by blunt scissor dissection, and the wound is apposed as a Y-shaped closure with 4-0 to 6-0 simple interrupted non-absorbable sutures (Fig. 5.42c).

Kuhnt–Szymanowski procedure The Kuhnt–Szymanowski procedure and the next two surgical techniques are used to correct the more severe forms of ectropion and can substantially shorten the lower eyelid. The Kuhnt–Szymanowski method consists of the excision of a wedge of conjunctiva and tarsus within the area of greatest ectropion, the excision of a wedge of orbicularis oculi muscle and skin at the lateral canthus, and the shortening of the lid with a sliding flap of orbicularis oculi muscle and skin. A major disadvantage of this procedure is that approximately the lateral two-thirds of the lower eyelid margin and eyelid must be split into palpebral conjunctiva–tarsus, and the orbicularis oculi muscle and skin layers. The lower eyelid is split with the No. 6700 microsurgical blade at the eyelid margin and immediately in front of the ‘gray line’ (opening of the meibomian glands), starting medial to the central area of ectropion and extending to the lateral canthus (Fig. 5.43a). The depth of the eyelid splitting should be about 10–15 mm. The skin incision is then continued into the lateral canthus to accommodate the excision of a wedge of skin approximately the same size as the tarsoconjunctival wedge (Fig. 5.43b). By tenotomy scissors a central wedge of tarsoconjunctiva is excised. The

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width of the wedge should be 0.5–1 mm shorter than the length of shortening for the lid (Fig. 5.43c). The tarsoconjunctival wound is apposed by a 4-0 to 6-0 simple continuous absorbable suture with the knots buried to avoid touching the cornea. The skin incision is apposed with 4-0 to 6-0 simple interrupted non-absorbable sutures. Just below the eyelid margin the split eyelid wound is apposed with 5-0 to 6-0 through-and-through interrupted mattress non-absorbable sutures with the knots on the skin side (Fig. 5.43d).

Kuhnt–Helmbold procedure Like the Kuhnt–Szymanowski technique, the Kuhnt– Helmbold method addresses ectropion by shortening the lower lid, but the surgery concentrates on the central portion of the eyelid. The lower eyelid is split at the ‘gray line’ into tarsus and palpebral conjunctiva, and skin–orbicularis oculi muscle layers with the No. 6500 microsurgical blade to a depth of about 10–15 mm (Fig. 5.44a). The length of the incision should include about 60–70% of the total lid length. Identical sized wedges of tarsoconjunctiva and skin–muscle are excised by small tenotomy scissors at two different locations (Fig. 5.44b). The tarsoconjunctival defect is apposed with 4-0 to 6-0 simple interrupted absorbable sutures. The skin–muscle wedge defect is apposed with 4-0 to 6-0 simple interrupted non-absorbable sutures. The lid margin wound is apposed with 4-0 to 6-0 through-and-through interrupted mattress non-absorbable sutures (Fig. 5.44c).

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Fig. 5.44 The Kuhnt–Helmbold procedure for ectropion. (a) The lower eyelid is split at the ‘gray line’ into tarsoconjunctival and skin–orbicularis oculi muscle layers to a depth of 10–15 mm. (b) Identical wedges of tarsoconjunctiva and skin–muscle are excised from the lower eyelid. (c) The tarsoconjunctival defect is apposed with 4-0 to 6-0 simple interrupted absorbable sutures. The skin–muscle layer is apposed with 4-0 to 6-0 simple interrupted non-absorbable sutures. The lid margin wound is apposed with 4-0 to 6-0 through-and-through interrupted mattress non-absorbable sutures.

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Fig. 5.45 The Munger and Carter modification of the Kuhnt–Szymanowski procedure for ectropion avoids splitting of the eyelid margin. (a) The skin incision is 3 mm below the eyelid margin and extends 10 mm beyond the lateral canthus. The skin–muscle flap is dissected from its deeper tarsal attachments. (b) Equal size wedges of tarsoconjunctiva and skin–muscle are excised by scissors. The tarsoconjunctival wound is apposed by a 4-0 to 6-0 simple continuous absorbable suture. (c) The skin–muscle defect and the remaining skin edges are apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures.

Modified Kuhnt–Szymanowski procedure (Munger and Carter) Both the Kuhnt–Szymanowski and Kuhnt–Helmbold ectropion procedures require a significant portion of the lower eyelid margin to be interrupted and then reapposed. The Munger and Carter modification of the Kuhnt– Szymanowski procedure permits the sliding and shortening of the lower eyelid but avoids splitting of the critical eyelid margin. The initial skin and orbicularis oculi muscle incision is made 3 mm from and parallel to the eyelid margin to approximately 10 mm lateral of the lateral canthus (Fig. 5.45a). A second skin–orbicularis oculi muscle incision is continued ventral for about 15 mm. The skin and muscle flap is undermined by small tenotomy scissors. A wedge of tarsus and palpebral conjunctiva, sufficient to shorten the lid and correct the ectropion, is excised by tenotomy scissors (Fig. 5.45b). The tarsoconjunctival defect is apposed with a 4-0 to 6-0 simple continuous absorbable suture. One additional suture is placed at the eyelid margin to maintain this apposition. A wedge of the skin and muscle flap is excised by tenotomy scissors. The size of this wedge approximates the tarsoconjunctival wedge. The skin–orbicularis oculi muscle flap is pulled dorsolaterally and the wound is apposed with 4-0 to 6-0 simple interrupted non-absorbable sutures (Fig. 5.45c). If the tension on the skin–muscle flap appears excessive, additional blunt–sharp dissection with tenotomy scissors should be performed. A few simple interrupted absorbable sutures attaching the flap edges to the deeper tarsus may be used to reduce the tension on the flap and skin sutures.

Postoperative management and complications Postoperative treatment after these ectropion procedures includes primarily topical antibiotics/corticosteroids for 10–14 days. Systemic antibiotics may be indicated for the more extensive procedures. The E-collar is used routinely to prevent the patient from rubbing the surgical site, producing local irritation and even suture loss. Partial and complete temporary tarsorrhaphies can provide some countertension for these procedures if necessary. All sutures should be removed at 7–10 days. The main goal of these procedures is to obtain a reasonable length lower lid and normal-appearing palpebral fissure. To avoid overcorrection and the more serious

entropion, the conservative approach is to slightly undercorrect the ectropion. Often the postoperative fibrosis about the surgical site will provide an additional 0.5– 1.0 mm correction. These procedures are frequently used in the large and giant breeds of dogs, and often globe contact with the lower eyelid is minimal or absent. Undercorrection of ectropion is recommended in these breeds to avoid postoperative entropion.

Ectropion in the horse Ectropion is defined as an outward rolling of the eyelid. This abnormality results in increased exposure of the cornea and conjunctiva. The most common cause in horses is contraction of scar tissue everting the eyelid following trauma and surgery. Several surgical techniques have been described for correction of ectropion in humans and in dogs. The most commonly used procedure in horses is the ‘V’ to ‘Y’ technique (see Fig. 5.42). The V portion of the incision is wide enough to extend slightly lateral and medial to the scar. The height of the V should be sufficient to remove the tension creating the ectropion. The skin beneath the V is undermined and the scar tissue is excised with tenotomy scissors. The apex of the V is pushed toward the eyelid margin to allow realignment of the eyelid, and closed to form a Y-shaped suture line with a single layer of simple interrupted sutures. Usually 4-0 to 5-0 non-absorbable suture material is used in the horse eyelid. Sutures are removed in 10–12 days.

Surgical procedures for combined ectropion and entropion Certain breeds of dogs, such as the Bloodhound, St Bernard, and Clumber Spaniel, are selected for ‘diamond’-appearing palpebral fissures that result in persistent conjunctival exposure and inflammation, impaired tear distribution on the ocular surfaces and to the nasolacrimal punta, lower entropion, lateral canthal entropion, and often heavy and excessive facial skinfolds and ears. Eyelid lengths, especially the lower, are excessive and the lateral canthus unstable, resulting in a sagging lower lid and inverted upper and lower lateral canthi. A poorly developed lateral canthal ligament or excessive tension on this area, as well as variable enophthalmia, are other complicating disorders.

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Surgeries to correct combined lower ectropion and lateral canthal entropion must include two concepts: 1) to shorten the lower lid; and 2) to stabilize the lateral canthus and correct the entropion. Available surgeries can effectively address the lower ectropion, but lateral canthal stability can still be a problem. Surgeries for combined ectropion–entropion include the traditional ectropion procedures, i.e., Wyman, the modified Kuhnt–Szymanowski, and the arrowhead entropion technique combined with wedge removal of the outer lower eyelid, and newer methods including those described by Gutbrod and Tietz, Bigelbach (can also be used for the medial canthus), and Bedford. The newer surgeries shorten the lower eyelid, and attempt to stabilize the lateral canthus and correct the entropion. In the Gutbrod–Tietz technique the lower eyelid is shortened and the lateral canthus is removed. In Bigelbach’s procedure a combined tarsorrhaphy–canthoplasty is used for either lateral or medial canthal disorders. Bedford modified the Kuhnt–Szymanowski procedure with additional splitting and resection of the upper eyelid. Combined ectropion–entropion patients are difficult to resolve and additional surgeries such as facial skin lifts or resections may be necessary.

the curve of the lower and upper eyelids, respectively, into the lateral canthus (Fig. 5.46c). A skin incision is used to connect the two incisions, creating a trapezoid shape; the skin-orbicularis oculi section is undermined and excised (Fig. 5.46d). The wound is then closed, resulting in a single vertical wound that is apposed with 4-0 simple interrupted sutures and a figure-of-eight suture at the new lid commissures (Fig. 5.46e,f). As dehiscence occurred in nearly 50% of the patients, a double-layer closure (palpebral conjunctiva–tarsus and orbicularis oculi–skin) is recommended, especially in large and giant breeds of dogs. If this procedure is used for the medial canthus, both the upper and lower lacrimal puncta are identified and avoided. Eyelid shortening in the medial canthal procedure is thereby limited to the distance the puncta are from the medical canthus. After this surgery, approximately 30% of the patients required additional surgeries (Hotz–Celsus, Stades, forehead skin resections) to help resolve the combined ectropion– entropion.

Bigelbach’s lateral tarsorrhaphy–canthoplasty

Bedford recently described a series of dogs treated with a modification of the Kuhnt–Szymanowski procedure in which the lower eyelid margo-intermarginalis is translocated to a new position above the lateral canthus to shorten the lower eyelid and help stabilize the lateral canthus. By two skin incisions by scalpel blade, a triangular skin flap is constructed at the lateral canthus (Fig. 5.47a,b). The 3–6 cm lower skin incision continues the curve of the lower eyelid; the lateral incision is 45 to the original lower skin incision and ends at the point determined to be the correct position for the lateral canthus. The skin flap is excised, leaving beneath the orbicularis oculi muscle. The lower and upper

In Bigelbach’s procedure the lower and upper eyelids can be shortened 20–25% in an attempt to stabilize the lateral or medial canthus. A trapezoid-shaped section of skin and orbicularis oculi muscle is excised from the lateral canthus (Fig. 5.46a). By scalpel blade, two 2 mm incisions are made perpendicular to the eyelid margins; the length of these incisions from the lateral or medial canthus will determine the extent of the eyelid shortening (Fig. 5.46b). Two curved skin incisions twice the length of the lid shortening are then made dorsally and ventrally, following

Bedford’s modification of the Kuhnt– Szymanowski technique

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Fig. 5.46 In the lateral tarsorrhaphy–canthoplasty method by Bigelbach, a trapezoid-shaped section of skin and orbicularis muscle is excised from the lateral canthus. (a) Two 2 mm scalpel incisions (A–B and B–C) are made perpendicular to the upper and lower eyelid margins. They mark the extent of the lid shortening. (b) A curved skin incision is extended from the lateral canthus following the curvature of the lower eyelid. (c) Similarly, a skin incision is performed from the lateral canthus following the curvature of the upper eyelid. (d) Additional skin incisions are used to extend the lid margin incisions and outer aspects of the curved skin incisions. These two wedges of skin are then excised. (e) The resultant surgical defect is trapezoid in shape, and the apposing edges are indicated by connecting arrows. (f) Two-layer closure (subcutaneous or tarsoconjunctival and skin) is recommended.

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Fig. 5.47 In Bedford’s modification of the Kuhnt–Szymanowski procedure, the upper eyelid is also shortened and incorporated into the lower lid and canthus surgery (which shorten the lower lid). (a) Following the curvature of the lower eyelid, a skin incision is constructed with its point at the new lateral canthus. (b) This skin flap is carefully dissected by scissors from its underlying cutaneous tissues. (c) The lower eyelid margin is incised into tarsoconjunctiva and skin–orbicularis oculi muscle layers for a distance that approximates the length of the lid shortening. (d) The two layers of the lid are separated by scissors toward the base of the lids to a depth of several millimeters and laterally to become confluent with the skin flap. (e) The upper eyelid margin is incised similarly, and its two layers (skin–orbicularis oculi and tarsoconjunctiva) separated by blunt scissor dissection. (f) From the upper eyelid, a wedge of outer skin–orbicularis is excised by scissors, with its tip at the new lateral canthus. (g) The base of the original skin flap is excised by scissors following the upper lid curvature. (h) In a similar fashion, the lower eyelid tarsoconjunctival wedge is excised. (i) The eventual edges that appose are indicated after the wedges and skin flap have been excised. (j) The deeper tarsoconjunctival layer is apposed to form the inner new lateral canthus with simple interrupted absorbable sutures (knots buried). (k) The remaining lower skin–orbicularis flap is shifted dorsally and laterally (to complete the shortening of the lids and raise the lateral canthus), and secured with simple interrupted non-absorbable sutures.

eyelid margins are split at the ‘gray line’ (opening of the meibomian glands) to a distance that equals the target shortening (Fig. 5.47c–e). The lower tarsoconjunctival and upper lid skin–orbicularis oculi muscle triangular flaps are excised, leaving overlapping lid sections (Fig. 5.47f–h). With both upper and lower eyelids shortened, the fellow tarsoconjunctival tissues are apposed with 6-0 simple interrupted absorbable sutures (Fig. 5.47i,j). The remaining lower skin–orbicularis oculi muscle flap is advanced dorsally and laterally into the triangular lateral canthal defect, and sutured in place with 3-0 to 4-0 simple interrupted non-absorbable sutures (Fig. 5.47k).

In a series of 22 dogs, including St Bernards (8), Bloodhounds (6), Clumber Spaniels (4), English Cocker Spaniels (2), and Neapolitan Mastiffs (2), surgical shortening of the eyelids was attained, but 5 dogs required additional forehead skin resections for optimum effect.

Grussendorf procedure In the procedure recently reported by Grussendorf, both the upper and lower eyelids are shortened, and the lateral canthus is repositioned and fixed by a traction suture at the lateral canthus in giant breeds of dogs. This procedure

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is a further modification of the Wyman lateral canthoplasty described previously. The excessively long upper and lower lids are shortened, up to one-third of their length, by removing the involved lid margins to permit shifting of the lids laterally, and removal as triangles of skin later. A linear skin incision is extended from the lateral canthus to 2 mm caudal of the lateral orbital ligament, and a new lateral canthus is created with a figure-of-eight non-absorbable suture connecting the lateral canthus and lateral orbital ligament. This suture is tightened to establish a normal-appearing lateral canthus. Any surplus upper and lower lid tissues are removed as skin triangles. The lateral canthal and lid wounds are closed by simple interrupted non-absorbable sutures, appearing as an ‘X’ or cross at closure.

OTHER SURGICAL PROCEDURES

Surgical procedures to decrease palpebral fissure size Surgical procedures to change the size of the palpebral fissure may involve the medial canthus, lateral canthus or, in severe cases, a combination of both areas. Surgical procedures at the medial canthus must first identify the problem area(s), and, often by cannulation with a 2-0 blue or green monofilament nylon suture, locate the lacrimal puncta and canaliculi. The lateral canthus is most accessible, but surgical sites in this area are more apt to atrophy with time. The lack of stability and the increased movements of the lateral canthal region may also complicate these surgical procedures by causing greater short-term stress on the suture line and long-term tension of the apposed eyelid tissues. For both the medial and lateral canthoplasty procedures the usual goal is to reduce the palpebral fissure by one-fourth to one-third. The overall size of the palpebral fissure can significantly influence the health of the conjunctiva and the cornea. Palpebral fissures that are larger than normal (euryblepharon) have eyelids (macroblepharon) that are potentially longer than normal. Enlarged palpebral fissures are often associated with an increased frequency of recurrent conjunctival and corneal diseases (Fig. 5.48). Breeds predisposed to macropalpebral fissures include the Bloodhound, St Bernard, English Cocker Spaniel, American Cocker Spaniel, and English Springer Spaniel. Macropalpebral fissures may be those in excess of 35 mm long, but this limit is relative until additional breed-related information is developed. Surgical reduction of normal sized palpebral fissures may be indicated in the brachycephalic breeds with exophthalmia, such as the Pekingese, Shih Tzu, and Lhasa Apso. These breeds often develop recurrent central corneal ulcerations that have the potential to progress and even perforate. The blink reflex may be weak and incomplete, resulting in a thin preocular film on the center of the cornea and an increased risk of epithelial loss. The retention of topical rose Bengal by the central cornea suggests that this region is at risk for ulceration and confirms the lagophthalmia. Surgical reduction in the size of the palpebral fissure may decrease corneal exposure and hopefully the possibility of recurrent corneal ulceration. Some of these dogs sleep with the central cornea exposed.

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Fig. 5.48 Pekingese with a melting corneal ulcer and lagophthalmos. As part of the clinical management of the corneal ulcer and abscess, surgical reduction in the size of the palpebral fissure is recommended.

Surgical techniques to reduce the size of the palpebral fissure include the lateral canthoplasty (modified Fuch’s), the Jensen/Roberts’ medial and lateral ‘pocket’ canthoplasties, and the lateral canthoplasty method by Wyman and modified by Kaswan. Most of the surgical techniques that address ectropion, as well as the combination of entropion and ectropion, also decrease the size of the palpebral fissure.

Medial canthoplasty The medial canthoplasty procedure reduces the size of the palpebral fissure by creating a permanent union of the medial upper and lower eyelids. As the length of the eyelid union increases, the size of the palpebral fissure decreases, but the correction is more limited with this method. Both upper and lower lacrimal puncta should be identified and, if desired, can be cannulated with short lengths of green or blue non-filament nylon suture. The medial canthal eyelid margin is everted, and the eyelid margin incised to a depth of 3–4 mm by the No. 6400 microsurgical blade, starting 1–2 mm medial of the lower lacrimal punctum and terminating 1–2 mm medial of the upper lacrimal punctum (Fig. 5.49a). Apposition of the surgical wound is by twolayer closure. The tarsoconjunctival layer is apposed by a 4-0 to 6-0 simple continuous absorbable sutures. The eyelid skin and muscle layer are apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures (Fig. 5.49b).

Pocket technique (Roberts and Jensen) The pocket technique, described by Roberts and Jensen, is technically more difficult; however, with the multiple layers of tissue apposition, the attachment of the upper and lower eyelids at the medial canthus is stronger. The technique can also be used to treat medial entropion of this area. Because this method uses a flap of palpebral conjunctiva to secure the lower pocket, the function of the upper lacrimal punctum is lost. This method can also remove the caruncle, and prevent the related medial trichiasis and epiphora. The pocket technique may also be used for the lateral canthus.

Surgical procedures to decrease palpebral fissure size

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Fig. 5.49 The medial canthoplasty procedure reduces the size of the palpebral fissure. (a) After identification of both upper and lower lacrimal puncta, the eyelids margins are incised to a depth of 3–4 mm by tenotomy scissors, starting 1–2 mm medial of the lower lacrimal punctum and terminating 1–2 mm medial of the upper lacrimal punctum. (b) The surgical wound is apposed by two layers of sutures for maximal strength. The tarsoconjunctival layer is apposed by a 4-0 to 6-0 simple continuous absorbable suture. The skin–orbicularis oculi muscle layer is apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures.

The upper and lower eyelids are split to a depth of about 10 mm at the ‘gray line’, starting 2–3 mm medial to the lower lacrimal punctum and continuing around the medial canthus, stopping 2–3 mm lateral of the upper lacrimal punctum, using the No. 6400 or No. 6700 microsurgical blade (Fig. 5.50a). Small tenotomy scissors may be used for the deeper aspects of the dissection to develop the ‘pocket’. A small strip of the skin portion of the split eyelid margins is carefully excised by tenotomy scissors (Fig. 5.50b). A triangular flap of palpebral conjunctiva is created by tenotomy scissors by cutting at a right angle at the lateral end of the split upper eyelid which sacrifices the upper lacrimal punctum. A 4-0 non-absorbable suture is inserted through the lower eyelid skin into the lower pocket, and then manipulated dorsally to emerge from the pocket (Fig. 5.50c). The suture is placed in the tip of the upper palpebral conjunctival flap, and then directed into the lower pocket to exit the skin. After the conjunctival flap is secured by suture, the upper and lower eyelid margins are apposed by 4-0 to 5-0 simple interrupted non-absorbable sutures (Fig. 5.50d).

Lateral reduction canthoplasty Lateral canthoplasty can reduce the size of the palpebral fissure by permanently apposing the eyelid margins for several millimeters at the lateral canthus. This procedure is also known as the lateral permanent tarsorrhaphy. Although

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Fig. 5.51 Permanent lateral canthotomy. (a) The upper and lower lid and the lateral canthal margins are excised by tenotomy scissors to a depth of 3– 4 mm: the longer the incision, the greater the reduction in the size of the palpebral fissure. (b) Two layers of sutures are used to appose the eyelid margins. The tarsoconjunctival layer is apposed by a 4-0 to 6-0 simple continuous absorbable suture. The skin–orbicularis oculi muscle layer is apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures.

technically easy, the tension on these apposed tissues appears greater than that at the medial canthus, and long-term atrophy of the surgical union may occur. The upper and lower eyelid margins are excised carefully by small tenotomy scissors, to a depth of about 3–4 mm (Fig. 5.51a). At this level both the meibomian glands and the pigmentation of the eyelid margins are excised, resulting in a continuous cover of eyelid hair over the surgical union. The length of the eyelid margins excised directly influences the reduction in the palpebral fissure. The upper and lower eyelid surgical wounds are apposed by a two-layer closure. The tarsoconjunctival layer is apposed by a 4-0 to 6-0 simple continuous absorbable suture. The eyelid skin and muscle layer is apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures (Fig. 5.51b).

Lateral canthoplasty (Fuch’s) The lateral canthoplasty, modified from Fuch, provides a stronger permanent union at the lateral canthus by rotating a section of lower eyelid skin and orbicularis oculi muscle into a lateral upper lid defect. The larger surgical surface area provides a stronger union for the permanent lateral canthoplasty. Both lateral upper and lower eyelids are split by the No. 6400 or 6700 microsurgical blade at the ‘gray line’ into outer skin and muscle, and inner tarsoconjunctival layers. The length of eyelid cleavage will determine the reduction in the size of the palpebral fissure (Fig. 5.52a). The medial

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Fig. 5.50 Medial ‘pocket’ canthoplasty procedure. (a) Both eyelids are split at the ‘gray line’ into tarsoconjunctiva and skin–orbicularis oculi muscle layers 2–3 mm medial of the upper and lower lacrimal puncta. (b) Small tenotomy scissors are used to remove the medial canthal eyelid margins and dissect 10–15 mm into the split lid. (c) A triangular flap of upper tarsoconjunctiva is fashioned by scissors and its leading edge apposed deep within the lower lid ‘pocket’ with a 4-0 simple interrupted non-absorbable suture. (d) After the upper conjunctival flap is secured in the lower ‘pocket’, the skin–orbicularis oculi layers are apposed with 4-0 to 5-0 simple interrupted non-absorbable sutures.

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Fig. 5.52 The lateral canthoplasty, modified from Fuch, rotates triangular sections of upper and lower lid skin and orbicularis oculi muscle. (a) The lateral portions of the upper and lower lids are split by the No. 6700 microsurgical blade. (b) A triangular section of upper eyelid is excised by tenotomy scissors. The lower eyelid is incised by tenotomy scissors, and its margin is excised. (c) The lower lid section is rotated into the upper lid defect. (d) The tarsoconjunctival layers are apposed with a 4-0 to 6-0 simple continuous absorbable suture. The lid skin and orbicularis oculi muscle layers are apposed with 4-0 to 6-0 simple interrupted non-absorbable sutures.

edge of the lower eyelid is incised by small tenotomy scissors to a depth of about 10–15 mm, and the lower lid margin is trimmed from this area (Fig. 5.52b). Triangular sections of the upper eyelid skin and muscle layer and the lower tarsoconjunctiva are excised by tenotomy scissors. The medial aspects of the upper tarsoconjunctiva and lower lid flap are rotated and apposed to the respective defects by two layers of sutures (Fig. 5.52c). The tarsoconjunctival layer is apposed by a 4-0 to 6-0 simple continuous absorbable suture. The external skin and muscle layer is apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures (Fig. 5.52d).

Lateral canthoplasty (Wyman and Kaswan) The lateral canthoplasty method by Wyman and modified by Kaswan, like the previous method, strengthens the permanent union of the lateral upper and lower eyelids by creating additional surface areas of the apposed tissues. A full-thickness incision of the upper eyelid is performed by tenotomy scissors at approximately one-fourth of the upper lid length (Fig. 5.53a). The upper eyelid margin and the corresponding length lateral lower eyelid margin are excised by scissors. A triangular section of lower lid skin is incised by the Beaver No. 6400 or 6700 microsurgical blade and excised by tenotomy scissors. A similar triangular section of palpebral conjunctiva from the lateral upper lid is excised by tenotomy scissors (Fig. 5.53b). The upper and lower palpebral conjunctival, tarsal, and subcutaneous layers are apposed by a 4-0 to 6-0 simple continuous absorbable suture (Fig. 5.53c). The apposing eyelid margins are attached by a

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single 4-0 to 6-0 interrupted mattress non-absorbable suture. The remaining skin flap is apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures (Fig. 5.53d).

Surgical procedures to increase palpebral fissure size Smaller than normal palpebral fissures have shorter than normal eyelids, and often lower and/or upper lid entropion and lateral canthal entropion. Breeds predisposed to micropalpebral fissures and the often concurrent entropion include the Chow Chow, Kerry Blue Terrier, Collie, Shetland Sheepdog, and the English Bull Terrier (Fig. 5.54). The surgical techniques to increase the size of the palpebral fissure may also address the entropion that often affects both the upper and lower eyelids. Surgical procedures to increase the size of the palpebral fissure include lateral augmentation canthoplasty and the arrowhead procedure combined with lateral canthotomy.

Lateral augmentation canthotomy Lateral augmentation canthoplasty increases the size of the palpebral fissure by a short incision of the lateral canthus and apposition of the incised eyelid surface. The procedure is quite similar to the lateral canthotomy. The lateral canthus is incised by tenotomy scissors for 5–10 mm (Fig. 5.55a). The length varies with the extent of the palpebral fissure enlargement. The palpebral conjunctiva is undermined in

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Fig. 5.53 Lateral canthoplasty by Wyman and modified by Kaswan. (a) Tenotomy scissors are used to incise the upper eyelid to full thickness (usually at the junction of the middle and lateral one-thirds of the eyelid), and excise the upper and lower eyelid and lateral canthal margins. (b) Corresponding but opposite triangular sections of lower eyelid and upper palpebral conjunctiva are excised by scissors. (c) The palpebral conjunctival wounds are apposed with a 4-0 to 6-0 simple continuous absorbable suture. (d) The skin–muscle layers are apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures.

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Surgical repair of eyelid lacerations

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Fig. 5.54 Micropalpebral fissure in a Chow Chow. (a) Often micropalpebral fissure is combined with entropion of the lateral portions of the upper and lower eyelids and the lateral canthus. (b) Correction of micropalpebral fissure and entropion in the Chow Chow with the arrowhead procedure and lateral canthotomy at 5 days postoperatively.

Nasal fold trichiasis and resection in dogs

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Fig. 5.55 The lateral canthotomy may be modified to increase the size of the palpebral fissure. (a) The lateral canthus is incised by scissors for 5– 10 mm. (b) The palpebral conjunctiva is undermined to the level of the fornix by tenotomy scissors, and apposed to the canthotomy wound by 4-0 to 60 simple interrupted non-absorbable sutures.

the area to the level of the fornix by blunt scissor dissection to line the edges of the new canthus. The palpebral conjunctiva is apposed to the new lateral canthus by 4-0 to 6-0 simple interrupted non-absorbable sutures (Fig. 5.55b).

Arrowhead procedure for entropion with lateral canthotomy The arrowhead procedure is detailed in a previous section under surgical correction of entropion. The lateral canthus can be incised as part of this procedure to increase the size of the palpebral fissure (Fig. 5.56). The edges of the lateral canthal wound are apposed to the adjacent palpebral conjunctiva.

Several brachycephalic breeds of dogs have large nasal folds whose hair may contact the medial nictitating membrane, conjunctiva, and cornea. The resultant low-grade chronic irritation results in epiphora and conjunctival hyperemia, inflammation, and pigmentation. The corneal sequelae include vascularization, pigmentation, and even ulceration. Medical treatment consists of the application of heavy petrolatum ointment and hair wax to paste the nasal fold hairs away from the eye. Surgical removal of the upper one-half or the entire nasal fold is the permanent method to prevent trichiasis. If medial entropion, exophthalmia, and lagophthalmia are present, reduction in the size of the palpebral fissure with one of the medial canthoplasty procedures should be considered. The base of the nasal fold is carefully inspected and then incised by Mayo scissors (Fig. 5.57a). Hemostasis is obtained by direct pressure with gauze sponges and, if necessary, by vessel ligation. The skin edges are apposed with 4-0 to 5-0 simple interrupted non-absorbable sutures (Fig. 5.57b). Special care is necessary to excise equal portions of both nasal folds to ensure symmetry (Fig. 5.58). Nasal skinfolds should not be removed in show dogs.

Surgical treatment of chalazion A chalazion is a chronic granulomatous inflammation of the tarsal or meibomian glands, and is presented as a swelling immediately beneath the palpebral conjunctiva. The recommended treatment for a chalazion is surgical drainage. After a short-acting injectable general anesthetic, the affected eyelid is grasped with a chalazion clamp (Fig. 5.59). After a short linear incision, the chronic tarsal adenitis and sebaceous secretions are curetted from the area. The wound is left to heal by secondary intention.

Surgical repair of eyelid lacerations

Fig. 5.56 The lateral canthotomy may be added to the arrowhead procedure for entropion to increase the size of the palpebral fissure.

Eyelid lacerations are not infrequent in all animal species, and often require surgical repair. Eyelid lacerations may be divided into partial and full thickness, and marginal and non-marginal. The eyelids are highly vascular and tissue debridement immediately prior to repair should be

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Fig. 5.57 Treatment of nasal fold trichiasis. (a) The nasal folds are carefully excised by curved Mayo scissors. (b) The wound edges are apposed with 4-0 to 5-0 simple interrupted non-absorbable sutures.

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Fig. 5.58 Postoperative appearance of a patient with the nasal folds removed. The left eye has exotropia, healed corneal ulcer, and optic nerve atrophy from a previous traumatic proptosis.

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Injuries at a 90 angle to the eyelid margin have a greater potential to affect eyelid function and cosmesis than injuries parallel to the lid margin (Fig. 5.60). The eyelid margin should be apposed as accurately as possible. Scar tissue at the eyelid margin can cause chronic irritation of the conjunctiva and cornea. Sutures at the eyelid margin should have their knots external to the ‘gray line’ to avoid contact with the cornea. Inflamed and swollen eyelids may develop temporary entropion. Two layers of sutures are recommended: an inner layer of simple continuous absorbable suture for the deeper palpebral conjunctiva and tarsus, and simple interrupted non-absorbable sutures for the external orbicularis oculi muscle and skin layer. A figure-of-eight suture pattern is recommended for lid margin injuries, and may be continued to the upper lid to provide tension on the injury site (Fig. 5.61). After any lid laceration of the medial canthus, the lacrimal puncta and canaliculi should be identified and flushed. In the event of transection, the opposing ends should be isolated and cannulated with 2-0 to 3-0 monofilament nylon. The nylon suture catheter should be left in position for 4–6 weeks or until the healing of the area is complete. After the repair of extensive eyelid injuries, a complete temporary tarsorrhaphy may be indicated to protect the cornea because of the impaired eyelid functions and blink reflex.

Eyelid trauma in the horse

Fig. 5.59 With the eyelid grasped by the chalazion clamp, the palpebral conjunctiva is incised and the contents of the chalazion are removed by curettage.

minimal. There are several guidelines for the surgical correction of eyelid injuries. All lacerations should be apposed by sutures. Lid healing by secondary intention may result in considerable fibrosis and distortion of the eyelids and lid margin that may eventually require surgical correction.

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The horse seems prone to eyelid lacerations from trapping the eyelid margin on metal rings, bucket handles, door latches, waterers, feed racks, lead shank clips, etc. Horses are particularly prone to eyelid lacerations because of the prominence of their eye and their tendency toward very sudden head movements when startled. When eyelid trauma is present or suspected, a thorough ophthalmic examination should be performed to rule out injury to other ocular structures. When hematomas or eyelid edema occur, initial treatment is with the use of ice packs, dimethyl sulfoxide applied to the eyelids, and administration of flunixin meglumine (1 mg/kg IV q24h). If eyelid closure is impaired or if facial nerve damage is present, a temporary tarsorrhaphy or nictitating membrane flap may be used to aid in the protection of the globe. If eyelid abrasions occur, topical antibiotic ointments are used.

Surgical repair of eyelid lacerations

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Fig. 5.60 Example of full-thickness eyelid lacerations in the dog. (a) Preoperative appearance of a recurrent lateral lower lid laceration. No tissue should be trimmed, and the lacerated lid carefully reapposed starting with the lid margin. (b) Appearance of a medial upper lid laceration that was improperly managed, and the lacerated lid excised. The remaining scarred lid is causing direct damage to the underlying cornea. Note the superficial corneal vascularization in the exposed cornea.

Fig. 5.61 The figure-of-eight suture pattern can be used to assist in closure of the tarsoconjunctival layer in vertical lid lacerations. The exact apposition of the eyelid margin helps reduce the likelihood of a postoperative notch.

Lacerations should be managed promptly to avoid distortion from severe swelling, inflammation, infection, scarring, and loss of function (Fig. 5.62). Lacerated tissue should not be excised. Even with the best plastic techniques, it is impossible to reconstruct the mucocutaneous junction of the eyelid margin. If eyelid margin is sacrificed, the occurrence

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of eyelid scar formation and secondary corneal damage is likely. Eyelid lacerations in the horse should be flushed with saline and cleaned to remove all foreign material. Lacerations less than 12 h old are cleaned and repaired as soon as practical. Older lacerations or longstanding infected wounds may be packed with an antibiotic dressing for 24–48 h and then closed. Intravenous flunixin meglumine is administered preoperatively. Eyelid lacerations may be repaired under general anesthesia, or standing with sedation and motor and sensory nerve blocks for the affected area of the eyelid. The wound is prepared with dilute povidone–iodine solution. Debridement should be limited; the wound edges may be scraped with a surgical blade or rubbed with a surgical sponge soaked in dilute povidone–iodine solution. Surgical scrub is not usually used on the wound. However, shampoos that are compatible with mucous membranes (baby shampoo) may be used to cleanse the surgical area. Any necrotic tissue should be excised, but wound debridement is minimal. Every attempt should be made to preserve the entire eyelid margin. Closure is performed in two layers; the tarsoconjunctival layer is closed with 5-0 to 7-0 polyglactin 910 in

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Fig. 5.62 (a) Preoperative appearance of a full-thickness upper eyelid laceration in a young horse. (b) Immediate postoperative appearance after a two-layer repair.

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a simple interrupted or continuous pattern. Suture knots are buried to prevent corneal irritation. The skin is closed beginning at the eyelid margin to prevent scar formation and irritation of the cornea. Usually 4-0 to 6-0 non-absorbable suture material is used in the skin. A figureof-eight suture is used to align the eyelid margin. The remainder of the skin wound is closed in a simple interrupted pattern or an alternating simple interrupted and vertical mattress suture pattern. Usually I leave the ends long on the first figure-of-eight suture and tie the ends into the knot of the interrupted suture adjacent to the eyelid margin suture. If there is significant eyelid swelling or lid closure is impaired, a complete temporary tarsorrhaphy may be indicated. Postoperative care of eyelid lacerations should include standard wound hygiene, application of fly repellent (if necessary), and the prevention of self-trauma. Topical and systemic antibiotics are indicated for 5–7 days. Tetanus prophylaxis should be verified by history or administered at the time of surgical repair. Placement of a subpalpebral lavage system will facilitate topical application of solutions to the eye. Postoperative swelling can be reduced by the administration of systemic non-steroidal anti-inflammatory agents (flunixin meglumine 1 mg/kg IV) immediately before surgery. Postoperative edema will be lessened by the application of ice packs for the first 24 h after surgery. If swelling is present 24 h after surgery, warm compresses may further reduce the swelling and discomfort at the surgical site. Dimethyl sulfoxide has been applied to the periorbital skin to reduce postsurgical swelling and discomfort. Rubbing or self-mutilation is often a concern in the horse, and the surgical site or eye must be protected by a protective hood with a plastic or solid eyecup (EyeSaver™, Jorgensen Laboratories, Loveland, CO.). Skin sutures are usually removed 8–12 days after surgery. In situations when tension on the suture line cannot be avoided, sutures are left in place for 18–24 days. Improper closure of eyelid lacerations may lead to abnormal function and complications, including chronic ulcerative keratitis, cicatricial entropion or ectropion, conjunctivitis, corneal fibrosis, and pigmentary keratitis.

Surgical procedures for minor eyelid neoplasms in small animals Variable size defects of the eyelids result from eyelid agenesis, the excision of congenital, inflammatory, and neoplastic masses, and eyelid loss after injuries. If these defects are less than one-third to one-fourth of the total eyelid length, apposition of the defect may be achieved by sutures. If the lid defect approximates up to one-third of the lid length, a ‘relief’ lateral canthotomy may decrease excessive lid tension. Some canine breeds, like the American and English Cocker Spaniels, have considerable eyelid length and sizeable defects can be accommodated by simple apposition. However, in other breeds, like the Doberman and Collie, surplus eyelid tissue is very limited, and similar size defects may require grafts. In cats, in contrast to dogs, most lid neoplasms are malignant and wider excision is necessary. In cats, the sliding or grafting of adjacent lid and facial tissue is often necessary as ‘surplus’ lid tissue is very limited. Although about 20–30% of canine eyelid neoplasms are malignant histologically, the majority are clinically benign.

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Fig. 5.63 Tarsal adenocarcinoma of the upper eyelid in a 10-year-old dog.

Certain neoplasms, however, such as the melanomas, should be resected and widely excised. The average age of dogs affected with eyelid neoplasia is about 8 years, and the Beagle, Siberian Husky, and English Setter appear to have a higher risk. The tarsal gland or meibomian adenoma and adenocarcinomas are the most frequent group of tumors (about 50%), and are best visualized by everting the lid and inspecting its palpebral surface (Fig. 5.63). Approximately 10% of canine malignant lid tumors are locally invasive and include melanoma, basal cell carcinoma, mast cell sarcoma, squamous cell carcinoma, and hemangiosarcoma. When the recurrence rates of all types of canine eyelid neoplasms were compared after surgical excision or cryotherapy, the mean recurrence rate after surgery was nearly 30 months. After cryotherapy, the mean recurrence rate was about 8 months. In contrast to the dog, eyelid malignancy in cats is high. Squamous cell carcinomas constitute about 60% of eyelid neoplasms, and the average age of affected cats is about 10 years (Fig. 5.64). Other malignant feline lid tumors include fibrosarcoma, adenocarcinoma, basal cell carcinoma, melanoma, and hemangiosarcoma. Feline eyelid neoplasms generally require rather wide excision. For feline squamous cell carcinomas of the eyelids, surgery is often combined with radiation and cryotherapy. The surgical techniques used to

Fig. 5.64 Squamous cell carcinoma of the lower eyelid and palpebral conjunctiva in an aged cat.

Surgical procedures for minor eyelid neoplasms in small animals

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Fig. 5.65 Full-thickness ‘V’ or wedge eyelid excision. (a) A wedge of affected eyelid is excised by tenotomy scissors. (b) The wound is closed by two layers of sutures. The tarsoconjunctival layer is apposed by a 4-0 to 6-0 simple continuous absorbable suture. The skin–orbicularis oculi muscle layer is apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures.

excise masses of the eyelids without grafts of adjacent tissues include the partial-thickness excision, the simple ‘V’ technique (full-thickness excision), and the four-sided method. In horses and cattle, the same eyelid surgical techniques can be readily adapted. Like cats, the majority of lid tumors are malignant, and surgery is combined with other modalities, such as local chemotherapy, to produce acceptable ‘cure’ rates in horses and cattle.

healing there is an obvious notch in the eyelid margin where the postoperative tension is greatest. The affected area of the lid may be grasped by a chalazion or entropion clamp. The sides of the eyelid neoplasm are excised by tenotomy scissors or a Beaver No. 6400 or 6700 microsurgical blade (Fig. 5.65a). Hemostasis is usually by direct pressure or point electrocautery. The wound is usually apposed by two layers of sutures. A 4-0 to 6-0 simple continuous absorbable suture is used to appose the tarsoconjunctival layer. The skin and orbicularis oculi muscle layer is apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures (Fig. 5.65b). The suture at the external aspect of the eyelid margin is the most critical for lid alignment and to reduce the likelihood of a notch developing postoperatively. In large dogs, an interrupted mattress or figure-of-eight suture is recommended. A relief lateral canthotomy may be necessary if the wedge of lid resection approximates one-third of the lid length. With upper lid surgical defects, a modified lateral canthoplasty may be performed (Fig. 5.66a). The removal of a triangle of skin from the lateral canthus permits the shift of this area to form a new lateral eyelid margin. The two sides of the skin triangle are apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures (Fig. 5.66b).

Partial lid thickness excision of eyelid masses Eyelid neoplasms may affect only the skin and subcutaneous layers, or the tarsal layer as with meibomian gland masses. Many of these masses can be excised conservatively without creating a full-thickness lid defect. Masses on the eyelid skin can be excised by scalpel using a circular or oval-shaped incision. Closure should be vertical or at 90 to the eyelid margin for lower lid defects and parallel to the upper lid margin to reduce the scar tissue effect on lid movement. Other skin flaps, such as the ‘Z’ plasty transpositional, pedicle, advancement, and rhombic types, can be used for partial-thickness lid defects after neoplasm removal. The eyelid may be grasped and everted by a chalazion clamp to expose tarsal or meibomian gland tumors. The tumor is excised by tenotomy scissors, and the palpebral conjunctival defect is left to heal by secondary intention.

‘V’ full-thickness excision The V-shaped full-thickness excision of eyelid neoplasms is frequently used for most types of canine eyelid neoplasms. The ‘V’ method is simple, but not infrequently after

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Four-sided full-thickness excision The four-sided full-thickness excision technique provides improved results compared to the ‘V’ type method. This procedure creates a larger surface area of the eyelid to distribute the tension associated with the apposition of the wound. The eyelid neoplasm is excised by tenotomy scissors to create a four-sided defect (Fig. 5.67a). The wound is apposed by two layers of sutures. The tarsoconjunctiva is apposed by a 4-0 to 6-0 simple continuous absorbable suture, and the skin–muscle layer by 4-0 to 6-0 simple interrupted nonabsorbable sutures (Fig. 5.67b).

Postoperative management and complications The usual postoperative treatment after the excision of small lid masses is topical antibiotics, often combined with topical corticosteroids. The E-collar is useful to prevent the patient from rubbing and possibly interrupting the surgical wound. The most frequent result after these procedures is the development of an obvious V-shaped notch at the eyelid margin. This can usually be avoided by use of the four-sided procedure.

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Fig. 5.66 A relief lateral canthotomy may be indicated when the ‘V’ shaped and four-sided full-thickness lid excision techniques are used. (a) The wedge removed approximates one-third or more of the eyelid length. After a lateral canthotomy is performed by scissors, a triangular skin flap is incised at the lower aspects of the lateral canthus with the Bard–Parker No. 15 scalpel blade. The skin flap is elevated from the subcutaneous tissues and excised by tenotomy scissors. (b) The skin flap edges are apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures. The new upper lid margin should be covered by palpebral conjunctiva, attached by a few 6-0 simple interrupted absorbable sutures.

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C Fig. 5.67 The four-sided full-thickness eyelid excision technique. (a) The lid mass is removed by tenotomy scissors, creating a four-sided surgical defect. (b) Wound closure is by two layers of sutures. The inner tarsoconjunctiva is apposed by a 4-0 to 6-0 simple continuous absorbable suture. The skin– orbicularis oculi muscle layer is apposed by 4-0 to 6-0 simple interrupted nonabsorbable sutures. The eyelid margin suture is carefully positioned on its outer aspects to avoid corneal contact and provide exact apposition of the eyelid margin. (c) Preoperative appearance of a large lid melanoma with its base at the lid margin. The mass was excised using the four-sided fullthickness technique. (d) Postoperative appearance several weeks later.

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Reconstructive blepharoplasty after removal of eyelid masses in small animals There are many different reconstructive blepharoplastic procedures available for small animals to repair defects that are one-third or more the length of the eyelid (Fig. 5.68). Some of these techniques include the sliding skin flap, sliding ‘Z’ skin flap, semicircular skin graft, pedicle skin graft, tarsoconjunctival graft, palpebral conjunctival graft (sliding and free), buccal mucosa grafts, rhomboid grafts, and the ‘bucket handle’ (Cutler–Beard) procedure. These blepharoplastic procedures can be modified for each patient, and are limited in application only by the skill and imagination of the veterinarian. Additional surgical procedures are available in the standard human oculoplastic surgery texts. The presence of the tarsal hyaline plate in humans presents additional opportunities as well as potential complications. The upper eyelid has the unique characteristics for the primary protection of the cornea, the major contributor for the blink reflex, the larger donor source of autogenous full-thickness lid and tarsoconjunctival tissues, the primary effect on the appearance of the eye, and in the dog the only place for cilia. The lower lid is smaller. Its primary function is to capture and hold the tears, and facilitate the medial movements of tears to the lower lacrimal punctum. A reasonable lower conjunctival fornix is essential to hold the tears.

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Eyelid and tarsoconjunctival grafts should be handled with care. Their bases should be wide to assist perfusion of the distal portion of the graft and prevent ischemia. After tissue grafts, 0.5–1.0 mm contraction usually occurs in small animals, and must be accommodated for in the blepharoplastic procedure. Movement of eyelid and tarsoconjunctival grafts should be limited to maximize successful transposition. Partial-to-complete temporary tarsorrhaphies are usually performed after reconstructive blepharoplasty in small animals. The closed eyelids reduce graft movement, prevent lid trauma to the graft edges, and can apply direct pressure to the deeper tarsoconjunctival and buccal mucosa grafts to reduce postoperative swelling. E-collars are essential after blepharoplasty to prevent the small animal patient from traumatizing the surgical site and prematurely removing the sutures.

Sliding skin flap The sliding skin flap or graft represents the most basic reconstructive blepharoplastic technique. It is used when surgical and traumatic eyelid defects are greater than one-third of the lid length. Sliding skin grafts should always be lined with mucosa harvested from adjacent conjunctiva or more remote sites. Sliding skin flaps are appropriate for both upper and lower lid defects. After full-thickness excision of the lid neoplasm by scissors or No. 6700 microsurgical blade, two slightly diverging

Reconstructive blepharoplasty after removal of eyelid masses in small animals

Fig. 5.68 Extensive meibomian adenocarcinoma of the upper eyelid of a dog. Close inspection of the palpebral aspect of this eyelid mass will determine whether conservative excision or reconstructive blepharoplasty is necessary.

skin incisions are performed approximately twice as long as the height of the defect (Fig. 5.69a,b). Two equal-sized triangles of skin (Burow’s triangles) are excised to accommodate shifting the graft into the defect (Fig. 5.69c,d).

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After liberal dissection to adequately separate the skin flap from its subcutaneous attachments, the skin flap is moved into the defect, thereby collapsing the Burow’s triangles (Fig. 5.69e). Before apposition of the skin flap, adjacent palpebral and fornix conjunctivae are mobilized to cover the deeper aspect of the skin flap. Other sources for mucosa to line the skin flap include the tarsopalpebral conjunctiva from the upper lid and a free or island graft of buccal mucosa. This dissection must provide adequate mucosa without any tension to avoid excessive fibrosis and inversion of the leading edge of the skin flap. After placement of the leading edge of the skin flap about 0.5–1.0 mm above the adjacent eyelid margin to compensate for postoperative shrinkage of the graft, the sides of the skin flap are apposed with 4-0 to 6-0 simple interrupted non-absorbable sutures (Fig. 5.69f,g). The conjunctiva is attached to the posterior aspects of the skin flap by 4-0 to 6-0 simple interrupted absorbable sutures with the knots buried or exposed on the eyelid flap skin. If some tension can be demonstrated on the skin flap, a complete temporary tarsorrhaphy is performed and left in place for 4–6 weeks to provide countertension.

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G Fig. 5.69 Sliding skin graft. (a) After full-thickness excision of the eyelid neoplasm, two slightly diverging skin incisions are continued from the base of the wound. These skin incisions should be twice as long as the defect’s height. (b) Intraoperative appearance, and removal of a full-thickness melanoma from the lower eyelid in a dog. (c) Two equal size triangles (Burow’s triangles) of skin are excised to facilitate shifting the graft into the surgical wound. (d) Intraoperative appearance, showing construction of the sliding skin graft. (e) After extensive subcutaneous dissection under the skin graft, the flap is moved into the wound. The leading edge of the skin graft should be 0.5–1.0 mm above the adjacent eyelid margin. (f) The skin graft is secured by 4-0 to 6-0 simple interrupted non-absorbable sutures. The posterior aspects of the skin graft must be lined with mucosa, from adjacent palpebral conjunctiva, buccal mucosa, or an island graft from bulbar conjunctiva of the opposite eye. (g) Immediate postoperative appearance, after completion of the lower sliding skin graft.

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‘Z’ plasty skin flap

Semicircular skin grafts

The ‘Z’ plasty is a modification of the sliding skin flap and is recommended for lateral defects of the upper eyelid. The neoplasm is removed by ‘en bloc’ excision by tenotomy scissors (Fig. 5.70a). After blunt–sharp dissection of the entire subcutaneous lateral canthus by scissors, two equilateral triangles of skin are excised by the Beaver No. 6700 microsurgical blade (Fig. 5.70b). The length of these skin triangles should be about 1 mm larger than the sides of the surgical defect. The skin flap is slid ventrally to fill the upper lid defect and collapse the lower skin triangle defect. The skin flap is apposed to the adjacent skin with 4-0 to 6-0 simple interrupted nonabsorbable sutures (Fig. 5.70c). The posterior aspect of the skin flap is lined by conjunctival mucosa, usually harvested from adjacent areas. The mucosa is apposed with a 4-0 to 6-0 simple continuous absorbable suture (Fig. 5.70d).

Semicircular skin grafts are used in dogs for restoration of surgical defects involving 30–60% of the center of the upper and lower eyelids. Semicircular grafts utilize both rotational and sliding components. Following full-thickness excision of eyelid neoplasms (Fig. 5.71a), the semicircular skin graft is constructed by a curved skin incision starting at the lateral canthus and of a length that approximates the width of the surgical defect (Fig. 5.71b). Excision of a Burow’s triangle of skin at the end of the semicircular graft allows medial movement without focal terminal distortion. In the areas in which the semicircular flap is not covered with conjunctiva, adjacent conjunctiva may be slid from the lateral canthal region and attached with absorbable sutures with the knots buried (Fig. 5.71c,d). In areas in which a new eyelid margin occurs, the potential for trichiasis arises.

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Fig. 5.70 The ‘Z’ plasty procedure is a modified sliding skin graft for the lateral canthal region. (a) The mass is removed full-thickness by tenotomy scissors from the lateral portion of the upper eyelid. (b) After blunt dissection of the subcutaneous tissues in the lateral canthus, two equal size triangles of skin are excised by the Beaver No. 6700 microsurgical blade. (c) The skin flaps are slid into position and secured by 4-0 to 6-0 simple interrupted non-absorbable sutures. The posterior aspect of the upper skin flap must be lined with mucosa from adjacent palpebral conjunctiva, buccal mucosa, or a free island bulbar conjunctival mucosa graft. (d) Three week postoperative appearance of a dog with a ‘Z’ plasty procedure after excision of a large neoplasm of the lateral aspects of the upper eyelid.

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D Fig. 5.71 Semicircular skin grafts may also be used to repair large eyelid defects. (a) The eyelid mass is excised full-thickness using the four-sided method, and a skin incision is extended to the lateral canthus (length approximates the width of the surgical defect). (b) A triangle (Burow’s) of skin is excised from the end of the skin incision, and the semicircular skin flap is dissected carefully from its underlying subcutaneous attachments. (c) The semicircular skin flap is slid medially, and the eyelid defect apposed by sutures, usually in two layers: tarsoconjunctiva (simple continuous absorbable) and muscle–skin (simple interrupted). The remainder of the graft is secured with simple interrupted non-absorbable sutures. The portion of the semicircular graft that forms the new lateral upper lid must be lined with palpebral conjunctiva. (d) Immediate postoperative appearance after an upper semicircular skin graft in a dog.

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Sliding skin flaps combined with tarsoconjunctival grafts For full-thickness eyelid defects that involve more than one-half of the length of the eyelid, a sliding flap adjacent to the surgical defect may be combined with a tarsoconjunctival graft from the opposite eyelid. The combined procedure may be used for either upper or lower lid defects. After removal of the lower lid eyelid mass, an upper tarsoconjunctival graft is constructed. About 2 mm beyond the eyelid margin, a broad pedicle graft of tarsoconjunctiva about 1 mm wider than the surgical defect is prepared by tenotomy scissors (Fig. 5.72a). After adequate preparation, the tarsoconjunctival graft is secured to the tarsoconjunctival layer of the surgical defect by 4-0 to 6-0 simple interrupted absorbable sutures (Fig. 5.72b). The sliding skin flap is then prepared as described in the earlier

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section (Fig. 5.72c). To secure and stabilize both grafts, a complete temporary tarsorrhaphy is performed and maintained for 4–6 weeks. If topical medications are necessary, a subpalpebral medication system is implanted in the upper conjunctival fornix.

Full-thickness lid flaps (‘bucket handle’ or Cutler–Beard method) For eyelid defects greater than one-half the length of the eyelid the full-thickness eyelid graft may be used. Although the upper lid has considerably more mass than the lower lid, full-thickness grafts may be provided by either eyelid. After the lower eyelid neoplasm has been excised, a full-thickness upper lid graft is prepared about 4–5 mm above the lid margin (Fig. 5.73a). The tip of the lid graft should be 0.5–1 mm

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Fig. 5.72 Sliding skin flaps involving one eyelid may be combined with tarsoconjunctival grafts from the opposite eyelid. (a) The lower eyelid neoplasm is excised full-thickness. The upper tarsoconjunctival graft is constructed to be slightly larger than the lower lid defect. About 2 mm from the eyelid margin, the palpebral conjunctiva and tarsus pedicle graft is prepared by tenotomy scissors. (b) The tarsoconjunctival graft is secured in the lower lid defect by 4-0 to 6-0 simple interrupted absorbable sutures. (c) The lower lid sliding skin graft is prepared as described in Figure 5.69. A temporary complete tarsorrhaphy is performed to immobilize the graft sites. The skin sutures are removed in 7–10 days. The tarsorrhaphy sutures are removed in 4–6 weeks and the base of the tarsoconjunctival graft is transected by tenotomy scissors. The upper tarsoconjunctival defect is allowed to heal by secondary intention.

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D Fig. 5.73 For full-thickness eyelid (‘bucket handle’ or Cutler–Beard technique) grafts, either the lower or upper eyelid may be used as the donor. (a) The full-thickness lid graft is constructed about 4–5 mm from the eyelid margin and should be 0.5–1 mm larger that the surgical wound. (b) The upper lid graft is positioned under (deep to) the strip of remaining upper lid margin and secured in the lower lid defect by two layers of sutures. The tarsoconjunctival layers are apposed by a 4-0 to 6-0 simple continuous absorbable suture. The skin–orbicularis oculi layer is apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures. (c) A complete temporary tarsorrhaphy is performed to stabilize the graft site. After 3–4 weeks all the skin and tarsorrhaphy sutures are removed, and the base of the full-thickness lid graft transected. The upper lid edges are reapposed by 4-0 to 6-0 simple interrupted non-absorbable sutures. (d) Two week postoperative appearance of a dog with a lower full-thickness eyelid graft to the upper eyelid. Note the remaining strip of upper eyelid and margin. The base of the graft will be transected in 2 weeks and reapposed to the remaining upper eyelid strip.

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larger than the surgical wound. The lid graft is manipulated under the upper lid leading margin and apposed to the lower lid defect by two layers of sutures (Fig. 5.73b). The tarsoconjunctival layers are apposed by 4-0 to 6-0 simple interrupted absorbable sutures. The external skin and muscle layers are apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures. A complete temporary tarsorrhaphy, apposing the remaining upper lid edge and lower lid, is performed to restrict eyelid movements and assist graft establishment (Fig. 5.73c). If topical medication is necessary for the eye, a subpalpebral system is implanted in the dorsolateral conjunctival fornix. After 3–4 weeks to permit establishment of the eyelid graft, all of the skin and tarsorrhaphy sutures are removed (Fig. 5.73d). The eyelid graft is transected 0.5 mm above the adjacent lower eyelid margin to compensate for shrinkage. The remaining upper lid is reattached to the upper lid margin by 4-0 to 6-0 simple interrupted non-absorbable sutures.

Large pedicle skin grafts Large pedicle skin grafts may be used in small animals in the surgical management of very large eyelid defects which result from the excision of locally malignant skin neoplasms. Because of the greater frequency of locally aggressive malignant tumors, the cat is more often treated by these large grafts than the dog. These skin grafts, harvested from nearby sites, must be carefully constructed to ensure a viable skin blood supply, especially at the tip or end of the graft (Fig. 5.74a,b). As the tip is often the eyelid, lower or upper, it must be lined with either nearby conjunctiva or buccal mucosa. As the grafts do not usually contain functional muscle, the blink reflex is usually absent and depends on the now mobile nictitating membrane for corneal protection in the cat. These skin grafts are often two-step procedures.

Postoperative management and complications After all of these rather extensive reconstructive blepharoplastic procedures, topical and systemic antibiotics are administered. If other corneal and conjunctival diseases are present,

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additional medications are administered directly to the eye or by subpalpebral systems (see Chapter 2). An E-collar is used as long as any sutures are present or until the tarsorrhaphy sutures have been removed. Warm and cold compresses may be used to reduce eyelid swelling and promote circulation to the grafts. The primary objective of these procedures is to obtain adequate eyelid function and appearance, and prevent recurrence of the lid neoplasm. Restoration to complete normalcy is not usually obtained. The usual postoperative appearance is an irregular but acceptable eyelid margin. Fibrosis and slight inversion of the new eyelid margin may develop and require minor resection of the outer skin to evert the area and prevent trichiasis. If tension of the skin flap is excessive, some ectropion of the lower lid may develop. Treatment is not usually necessary as long as epiphora and chronic conjunctivitis do not develop.

Surgeries for eyelid neoplasia in the horse Several different eyelid tumors have been reported in the horse. These include squamous cell carcinomas, equine sarcoids, papillomas, melanomas, fibromas, schwannomas, basal cell carcinomas, hemangiosarcoma, lymphosarcomas, mastocytomas, and adenocarcinomas. Approximately 10% of all equine neoplasms are related to the eye. Squamous cell carcinoma is by far the most common ocular tumor in the horse, followed by sarcoids and papillomas. The other reported tumor types are considered rare in occurrence. Biopsy and histopathology or fine needle aspiration for cytologic interpretation is recommended to differentiate the tumor types and to distinguish them from inflammatory lesions before multiple therapies. Papillomas usually occur in young horses; they are commonly self-limiting, and do not require surgical excision. Squamous cell carcinomas affect the eyelids, nictitating membrane, and globe (Fig. 5.75). Lesions may be bilateral but are usually not symmetrical. Draft breeds (especially Belgians), Appaloosas, and horses with decreased eyelid pigmentation appear to be predisposed. The average age of horses presented with squamous cell carcinoma (SCC) is 8–11 years. Males are twice as likely as females to be affected,

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Fig. 5.74 Postoperative appearance after large skin grafts in the cat for large malignant eyelid tumors involving the entire lower or upper eyelid, or canthi. (a) Upper pedicle skin graft 2 weeks after surgery and removal of a large squamous cell carcinoma. (b) Upper and lower pedicle grafts 1 week after surgery and removal of a large squamous cell carcinoma of the lateral canthus, and lateral upper and lower eyelids.

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Blepharoplastic procedures for the horse

Fig. 5.75 Squamous cell carcinoma of the entire lower eyelid in a horse.

and geldings are five times more likely to have SCC than stallions. Coat color, such as white, cremello/palomino, gray, strawberry/white, buckskin and chestnut/sorrel, also predisposes to SCC. Although the tumor is aggressive locally, its metastatic rate is low (6–15%), with the regional submandibular lymph nodes, salivary glands, thorax and orbit, sinus, and calvaria affected. Sarcoid is the second most common tumor of the eyelid and the most common tumor observed in horses. Sarcoids are divided into several clinical groups; they include occult, verrucose, nodular, fibroblastic, and mixed types. Molecular biology techniques have confirmed the presence of bovine papilloma virus DNA in a high number of equine sarcoids. Predisposition is seen in the American Quarter Horse, Arabian, and Appaloosa breeds. Periocular sarcoids are often proliferative, may have nodules, may have a broad base or be pedunculated, may infiltrate into deeper tissues, and may be ulcerative. Sarcoids affect both upper and lower lids (Fig. 5.76). Some sarcoids may undergo spontaneous regression.

Blepharoplastic procedures for the horse Several surgical and blepharoplastic procedures are available for horses affected with either SCC or sarcoid. Choice of the specific surgical procedure as presented below often depends on the size and location of the mass, vision status, intended use of the animal, available equipment, prior experience of the veterinarian, value of the animal, and owner financial constraints. Retrospective studies strongly

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Fig. 5.76 Sarcoid affecting the lateral lower eyelid and lateral canthus.

suggest that surgical excision or debulking, combined with some form of adjunctive therapy, provides better long-term recurrence-free status than surgery alone.

Four-sided excision Masses that can be excised by removing one-third of the eyelid or less can be removed by ‘four-sided’ excision of tissue and direct closure of the wound (Fig. 5.77). The margins of the mass are excised perpendicular to the eyelid margin and connected with two angled incisions. The tarsoconjunctiva is closed with a 6-0 simple continuous absorbable suture, beginning at the distal incision, and the skin–muscle layer apposed with simple interrupted nonabsorbable sutures.

Reconstructive blepharoplasty Blepharoplasty techniques are indicated when more than one-third of the eyelid margin has been removed. These procedures are best performed with the horse under general anesthesia. When considering extensive blepharoplastic techniques in the horse, it should be noted that although the eyelid skin is very mobile, the surrounding facial skin is relatively immobile and may not slide to provide good donor tissue for eyelid defects. The skin is apposed with 5-0 nylon beginning at the eyelid margin. The eyelid margin is closed in a figure-eight suture using 5-0 nylon or silk. The remainder of the incision is closed with non-absorbable sutures in a simple interrupted pattern.

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Fig. 5.77 Four-sided or wedge excision of a very small squamous cell carcinoma of the central lower eyelid in a horse. (a) Preoperative appearance prior to wedge excision and after marking the incision line. (b) The tumor is excised by scalpel and scissors. (c) Appearance of the surgical wound as the tumor is removed. The wound was apposed with three simple interrupted skin sutures.

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Sliding skin graft or ‘H’ plasty One of the easiest forms of blepharoplasty is the sliding skin flap (see Fig. 5.69). The affected lesion is removed and the incisions are extended for twice the amount of skin removed. The incision is slightly diverging to allow for skin contracture after surgery (Fig. 5.78). These divergent incisions are not absolutely necessary in eyelid skin, due to its relative pliability and plasticity. Triangular pieces of skin are excised external to the base of the incisions. These triangular skin excisions allow skin closure without puckering of the skin (‘dog-ears’) and distribute the tension on the skin. The sides of the triangle should approximate the height of the excised triangle. Adjacent skin should be undermined to provide mobility for skin closure. Palpebral conjunctiva adjacent to the wound is undermined and mobilized utilizing Steven’s tenotomy scissors. The eyelid defect is slightly overcorrected to allow for wound contracture. There should never be tension on the conjunctival portion of the skin at closure. The conjunctiva is sutured using 6-0 polyglactin in a continuous pattern. Skin closure begins at the eyelid margin, utilizing an interrupted pattern of 4-0 to 5-0 nonabsorbable material. The skin is anchored to the conjunctiva using 6-0 polyglactin in a mattress or continuous pattern with buried knots to avoid irritation of the cornea. A temporary tarsorrhaphy is performed and left in place for 7–10 days to provide support for the skin flap during the initial healing phase.

Tarsoconjunctival advancement graft When large areas of palpebral conjunctiva are excised, a tarsoconjunctival advancement flap from the opposing eyelid is used to fill the conjunctival defect. This is a twostage procedure. The affected area of eyelid is excised and the sliding skin flap prepared as described above. Instead of using adjacent conjunctiva to line the defect, tarsoconjunctiva from the opposite eyelid is used to line the defect. The donor conjunctiva is incised 4 mm from the eyelid margin. The conjunctiva is dissected from a flap to fill the recipient area using Westcott or Steven’s tenotomy scissors. The tarsoconjunctiva is sutured across the eyelid to fill the defect, and then the skin is advanced to cover the defect. A few anchoring sutures are used in the donor graft to anchor

the conjunctiva. A temporary tarsorrhaphy is necessary to relieve tension on the conjunctiva in this procedure. A second surgical procedure is required to cut the conjunctival flap at the eyelid fissure to restore the eyelid margin. Cutting of the conjunctival flap is usually performed no earlier than 3 weeks after the initial surgery. It may be advantageous to the leave the flap in place for 4–6 weeks, or longer, after the primary surgery.

Full-thickness eyelid graft (Cutler– Beard procedure) A full-thickness eyelid flap is used for neoplasia or traumatic defects involving the lower eyelid where eyelid and facial skin are less mobile. A flap of more mobile and pliable upper eyelid is used. The width of the flap approximates the width of the eyelid defect. The lower eyelid lesion is excised as in the sliding skin flap technique. In more extensive defects, a lateral canthotomy is helpful to release tension at the surgical site. The opposing eyelid is incised about 5–6 mm from the eyelid margin, preserving the tarsal glands. Splitting the flap into skin–muscle and tarsoconjunctiva sections facilitates mobility and reduces the size of the graft required. The tarsoconjunctival portion of the flap is sutured using 6-0 to 7-0 polyglactin 910, with the knots buried away from the cornea to prevent irritation. The skin wound is closed with simple interrupted sutures of 4-0 to 5-0 nylon, prolene or silk. The bridge portion of skin is sutured to the flap using 5-0 nylon. The flap is left in place for several weeks (usually 4–8) until tension has normalized. In a second procedure, the flap is transected in line with the original eyelid margin and sutured to the bridge with 6-0 to 7-0 material. The newly created eyelid margin is sutured to appose the conjunctiva and skin with 6-0 to 7-0 polyglactin 910 (VicrylW). A temporary tarsorrhaphy is placed to prevent tension on the flap. The tarsorrhaphy can be removed in 3–4 weeks or left in place until the flap is incised in the second procedure to form the new eyelid margin.

Rhomboid graft Blanchard et al described a rhomboid graft flap for repairing defects of more than 50% of the eyelid (a rhomboid is an equal-sided parallelogram). One side of the rhomboid is used to recreate the eyelid margin. The replacement flap is made by two incisions: the first is an extension of the diagonal of the rhomboid and equal in length to the sides of the rhomboid; the second incision is made parallel to the rhomboid for an equal length. Palpebral or bulbar conjunctiva is undermined to cover the replacement skin flap. The skin is undermined and rotated to fill the defect. The conjunctiva is sutured to the skin to form an eyelid margin in a simple continuous pattern using 6-0 polyglactin material. The skin is closed in a simple interrupted pattern using 4-0 to 5-0 non-absorbable material.

Sliding ‘Z’ graft

Fig. 5.78 Immediate postoperative appearance after a large ‘H’ plasty for squamous cell carcinoma of the entire lower eyelid in a horse.

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Large defects in the lateral upper eyelid that occur after excision of eyelid tumors can be closed with a sliding ‘Z’ flap. Prior to excision of the lesion, the proposed excision area is marked with a CO2 laser, ophthalmic electrocautery, or

Blepharoplastic procedures for the horse

with surgical marking ink. Two triangles of skin, one above and one below the defect, are also marked. The lesion (mass) is excised. Adjacent skin is undermined with surgical scissors. Conjunctiva is undermined and mobilized to fill the defect, and closed with 6-0 to 7-0 VicrylW. The two triangles, which are equal to the sides of the excised defect, are then excised. Conjunctiva is undermined and mobilized to fill the defect, and sutured to the free skin edge with 6-0 to 7-0 VicrylW. The skin is apposed with 4-0 to 5-0 nylon in a simple interrupted pattern.

Partial orbital rim resection In 2002, Beard and Wilkie described a technique of enucleation or exenteration combined with a partial orbital rim resection and mesh skin expansion to fill the skin defects. Following enucleation or exenteration and radical excision of periocular skin, there may be inadequate tissue to close the wound using more conventional reconstructive and flap techniques. In this procedure, a portion of the dorsal rim of the orbit is resected after globe removal to decrease the wound area and reduce the tension on the skin sutures. Extensive undermining of the adjacent skin is performed and mesh skin expansion is added to allow advancement and closure of the wound.

Aftercare for blepharoplasty in the horse The general protocol for aftercare after blepharoplasty is similar to that for skin and reconstructive procedures elsewhere on the body. Pre- and perioperative topical and systemic antibiotics are indicated. The placement of a subpalpebral lavage system will facilitate topical application of solutions to the eye. Postoperative swelling will be reduced by the administration of systemic non-steroidal anti-inflammatory agents (flunixin meglumine 1 mg/kg IV) immediately before surgery. Postoperative edema will be lessened by the application of ice packs for the first 24 h after surgery. If swelling is present 24 h after surgery, warm compresses may further reduce the swelling and discomfort at the surgical site. As rubbing or self-mutilation is always a concern in horses, the surgical site or eye must be protected by a protective hood with a plastic or solid eyecup (EyeSaver™, Jorgensen Laboratories, Loveland, CO.). Cross tying or neck cradles have also been used successfully. If granulating wounds are present, removal of the exudate once or twice daily, with application of petroleum jelly or a povidone– iodine gel ventral to the wound is helpful, and fly-control is essential in warmer climates. Fly control around the horse’s face is achieved by wiping fly repellent around the surgical site, by fitting the horse with a fly mask, or by using fly-repellent strips attached to the halter. Skin sutures are usually removed 8–12 days after surgery. In situations when tension on the suture line cannot be avoided, sutures are left in place for 18–24 days.

Adjunctive therapeutic modalities which can be combined with surgery for the horse For eyelid squamous cell carcinoma and sarcoid in horses, surgical removal of these tumors generally results in about 50% non-recurrence with a single year follow-up.

Squamous cell carcinoma Of the different sites in the horse for SCC (eyelid, orbit, limbus, and nictitating membrane), the eyelids have the poorest prognosis, with an average of 30–40% recurrence rate. Perhaps one reason for the poorer prognosis with eyelid SCC is the fact that they are often presented as large masses and ‘clean’ surgical margins are not possible. Mean survival time after diagnosis is 47 months. The recommendation of a 2 cm tumor-free margin for surgical excision of the lids is generally impossible. As a result, surgery is often limited to biopsy or debulking of the mass, and then some form of adjunctive therapy. These adjunctive therapies depend on the size and location of the tumor, vision status of the patient, prior experience of the veterinarian, value of the animal, and owner financial constraints. These therapeutic options include cryotherapy, radiofrequency hyperthermia, intralesional (intratumoral) injections of biologic modifiers (usually mycobacterial cell wall fraction or bacille CalmetteGue´rin (BCG)), intralesional chemotherapy using cisplatin, and radiotherapy (using cesium-137, cobalt-60, gold-198, iridium-192, and strontium-90.)

Cryotherapy Cryotherapy is performed using liquid nitrogen as the refrigerant, either as a spray or solid probe delivery system, to freeze tissues to –20 C to –40 C, using either a double or triple freeze–thaw technique. The tissue should be allowed to completely thaw between freeze cycles. Use of a thermocouple to monitor the depth of freezing for larger masses is recommended. A heavy layer of petrolatum or a piece of styrofoam is used to protect the surrounding area from freezing. The iceball should extend at least 3–5 mm beyond the mass’s base. Even with the sloughing of cryonecrotic tissues within 2–4 weeks, the eyelid is usually able to heal and maintain its architecture and function following cryotherapy. Cryotherapy combined with surgery for lid SCC in horses has about 30–100% nonrecurrence rate.

Radiofrequency hyperthermia Radiofrequency employs a device that uses either a surface or a piercing probe to heat the tumor to 50 C (122 F) for 50 s; tumor cells are selectively destroyed over normal cells. Multiple application sites are needed if the mass exceeds 0.5 cm in diameter, and therapy should extend 3–4 mm beyond the mass’s base. Tumors in excess of 5 cm in diameter are not candidates for hyperthermia. Reports suggest about 75% complete regression after one treatment; for two treatments 66% completely regressed.

Immunotherapy Immunotherapy has been used successfully for equine eyelid SCC using BCG cell wall extract. The usual dose for BCG is 1 mL extract/cm3 of tumor injected throughout the mass. Treatments are spaced every 2–4 weeks, and continued until the mass has completely regressed. Both systemic and local anaphylaxis have been reported, and pretreatment with flunixin meglumine, antihistamine or corticosteroids may be necessary. This therapy has a high rate of tumor non-recurrence.

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Fig. 5.79 Intralesional/intratumoral chemotherapy with cisplatin for eyelid squamous cell carcinoma (SCC) in a horse. (a) Appearance of the SCC before cisplatin intratumoral therapy. (b) Appearance of the tumor after the second of four cisplatin injections. After the last cisplatin injection, the region will be assessed for regression and after biopsy has indicated that the area is tumor free.

Intralesional/intratumoral chemotherapy

Carbon dioxide laser

Intratumoral injection of cisplatin has been used successfully for treating lid SCC in horses, and has partly replaced the BCG technique. The usual cisplatin dose is four injections at 2-week intervals with 1 mg cisplatin (3.3 mg/mL; 10 mg cisplatin in 1 mL water and 2 mL of purified medical grade sesame seed oil) which should extend about 1 cm beyond the tumor margin (Fig. 5.79). Complete face protection from any cisplatin spray during the injection technique is required to prevent exposure of administering personnel to the drug especially after the first series of injections. The non-recurrence rate is about 65–90%. 5-Fluorouracil (5-FU) has also been used for intralesional treatments of SCC in the horse: 10 mL 5-FU (50 mg/mL), combined with 3 mL of 1:1000 adrenaline (epinephrine). Intratumoral bleomycin has also been compared to cisplatin, but is more expensive and perhaps not as successful (1 year follow-up: cisplatin 93% non-recurrence; bleomycin 78% non-recurrence).

Carbon dioxide laser has been reported for equine lid SCC, applied after tumor debulking. Laser settings were 3 and 8 W, and the tumor surface was lasered (ablated) until covered with a brown char.

Radiation therapy Radiation therapy with beta radiation (strontium-90) and brachytherapy with cesium-137, gold-198, radon-222, cobalt-60, and iridium-192 have been reported for equine lid SCC. Beta radiation has limited penetration (and is primarily used for corneoconjunctival SCC), but the brachytherapy agents are generally placed directly within the eyelid mass. The iridium-192 isotope, contained in stainless steel rods at 1 cm intervals in a plastic coating or within needles, is placed in the SCC mass in parallel rows about 1 cm apart (Fig. 5.80). The usual dose is 6000–7000 cGy and requires about 7–10 days of implantation. Unfortunately, availability, transportation and material costs, radiation exposure to personnel, isolation of the patient, and state radiation safety guidelines are important limitations. Brachyradiation yields the highest success rate for lid SC in the horse, and has well over 95% non-recurrence. Complications of brachytherapy include hair loss, hair and skin depigmentation, necrosis, fibrosis, keratitis, cataract formation, and corneal ulceration.

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Sarcoid Sarcoids, like SCC, have an unacceptably high rate of recurrence of about 50% after surgery alone. Hence, like SCC, adjunctive therapies are necessary to treat this tumor group successfully. Sarcoids tend to occur in young horses (3–6 years old); in contrast, SCCs occur in older horses (7–10 years old). Sarcoids are locally aggressive and tend to recur.

BCG immunotherapy The same menu of therapeutic choices used to treat SCC is used for sarcoids. Surgery is used to biopsy and debulk sarcoids before commencing these adjunctive therapies. The most common sarcoid therapy is immunotherapy using multiple injections of BCG (1.0 mL/cm2 of tumor surface). These injections, within the mass as well as at its borders, are repeated at 2- to 4-week intervals, and continue until complete regression of the tumor (Fig. 5.81). Both systemic

Fig. 5.80 Brachytherapy of a large upper eyelid squamous cell carcinoma using iridium-192. The stainless steel needles, about 1 cm apart, contain the iridium 192 isotope. Treatment exposure (usually 7–10 days) is dependent on the calculated total radiation dose.

Bovine eyelid surgery

in North America. It occurs in Hereford, Hereford crosses, Simmental and Shorthorn breeds; other breeds are affected infrequently. The economic impact includes carcass condemnations, production costs, treatment costs, and management expenses.

Surgery and surgery combinations for eyelid SCC in cattle

Fig. 5.81 Treatment of sarcoid with intralesional/intratumoral BCG injections. The needles have been pre-placed to ensure adequate coverage of the mass with the BCG injections.

and local anaphylaxis have been reported, and pretreatment with flunixin meglumine, antihistamine or corticosteroids may be necessary. One study reported complete regression of all sarcoids with an average of 3.2 treatments (11.7 mL per treatment) with a range of 14–253 days to resolve. Immunotherapy with BCG seems most effective for the fibroblastic and nodular types of sarcoid.

Intratumoral (intralesional) chemotherapy Intralesional cisplatin is now the most common local chemotherapy method for sarcoids. Multiple injections of the cisplatin oily emulsion (1 mg cisplatin/cm3 tumor tissue) are administered four times at 2-week intervals. In one report, complete regression occurred in 95% of the sarcoids, with 1-year relapse-free non-recurrence of 87%. Another report noted 33% non-recurrence.

Cryotherapy and radiofrequency hyperthermia Both of these therapies are administered as for SCC. Information about effectiveness for sarcoids is unknown.

Brachytherapy

Several treatment modalities are available; choice depends on availability of instrumentation, training of the veterinarian, location and size of the tumor, intended use of the animal, and value of the animal. Therapeutic choices include radiofrequency hyperthermia, immunotherapy, cryotherapy, radiation, CO2 laser ablation, and intralesional chemotherapy using cisplatin. Of these modalities, the lower cost cryotherapy and hyperthermia are used most frequently in cattle, combined with surgical debulking of the mass (see above section on the horse).

Sliding skin graft or ‘H’ plasty One of the frequent forms of blepharoplasty in cattle is the sliding skin graft. The lid mass is excised, and often treated by cryotherapy (Figs 5.82 and 5.83). The skin incisions are then extended for twice the amount of skin removed. The incision diverges slightly to allow for skin contracture after surgery. These divergent incisions are not absolutely necessary in eyelid skin, due to its relative pliability and plasticity. Triangular pieces of skin are excised external to the base of the incisions. These triangular skin excisions allow skin closure without puckering of the skin (‘dog-ears’) and distribute the tension on the skin. The sides of the triangle should approximate the height of the excised triangle. Adjacent skin should be undermined to provide mobility for skin closure. Palpebral conjunctiva adjacent to the wound is undermined and mobilized utilizing Steven’s tenotomy scissors. The width and length of the eyelid defect are slightly overcorrected to allow for wound contracture. There should never be tension on the conjunctival portion of the skin at closure. The conjunctiva is sutured using 6-0 polyglactin in a continuous pattern. Skin closure begins at

Like squamous cell carcinomas in horses, brachytherapy is effective to treat all forms of sarcoid. Several forms of isotope have been used. Iridium-192 has been reported most frequently, and for sarcoids provides a non-recurrence rate as high as 94% at 1 year. The usual radiation dose is 5000–9000 cGy and requires 7–14 days of implantation. High costs and restricted availability are the main limitations.

Bovine eyelid surgery Eyelid SCC, as part of ocular squamous cell carcinoma (OSCC), is the most frequent indication for lid surgery in cattle. Eyelid lacerations occur infrequently in cattle, and are repaired in a similar fashion to horses and small animals. Ocular squamous cell carcinoma in cattle, often termed cancer eye, is the most economically important neoplasia in cattle. It is the most common neoplasm affecting cattle

Fig. 5.82 Intraoperative photograph of ‘H’ plasty in a cow with squamous cell carcinoma of the entire lower lid. The skin graft has been advanced into the surgical wound.

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Fig. 5.83 Three different delivery probes for liquid nitrogen and cryotherapy in cattle. (a) Use of a small direct contact cryoprobe for a limbal squamous cell carcinoma. (b) Intraoperative photograph of a large direct contact cryoprobe used after debulking a large lower eyelid squamous cell carcinoma. (c) Intraoperative photograph using liquid nitrogen spray for squamous cell carcinoma after debulking the mass affecting the lower eyelid. Adjacent normal tissues are protected from the nitrogen spray with a thick coat of petrolatum gel.

the eyelid margin, utilizing an interrupted pattern of 4-0 to 5-0 non-absorbable material. The skin is anchored to the conjunctiva using 6-0 polyglactin in a mattress or continuous pattern with buried knots to avoid irritation of the cornea. A temporary tarsorrhaphy is performed and left in place for 7–10 days to provide support for the skin graft during the initial healing phase.

is necessary to relieve tension on the conjunctiva in this procedure. A second surgical procedure is required to cut the conjunctival flap at the eyelid fissure to restore the eyelid margin. The cutting of the base of the conjunctival graft is usually performed no earlier than 3 weeks after the initial surgery. It may be advantageous to the leave the flap in place for 4–6 weeks after the primary surgery.

Tarsoconjunctival advancement graft

Full-thickness eyelid graft

When large areas of palpebral conjunctiva are excised, a tarsoconjunctival advancement graft from the opposing eyelid is used to fill the conjunctival defect. This is a two-stage procedure, as described in the horse. A temporary tarsorrhaphy

A full-thickness eyelid flap is used for neoplasia or traumatic defects involving the lower eyelid where eyelid and facial skin are less mobile. The procedure is identical to that in the horse.

Further reading Small animals Barrie KP, Gelatt KN, Parshall CP: Eyelid squamous cell carcinoma in four dogs, J Am Anim Hosp Assoc 18:123–127, 1982. Bedford PGC: Eyelashes and adventitious cilia as causes of corneal irritation, J Small Anim Pract 12:11–17, 1971. Bedford PGC: The treatment of canine distichiasis by the method of partial tarsal plate excision, J Am Anim Hosp Assoc 15:59–60, 1979. Bedford PGC: Conditions of the eyelids in the dog, J Small Anim Pract 29:416–428, 1988. Bedford PGC: Surgical correction of facial droop in the English Cocker Spaniel, J Small Anim Pract 31:255–258, 1990. Bedford PGC: Technique of lateral canthoplasty for the correction of macropalpebral fissure in the dog, J Small Anim Pract 39:117–120, 1998. Bedford PGC: Diseases and surgery of the canine eyelid. In Gelatt KN, editor: Veterinary Ophthalmology, ed 3, Baltimore, 1999, Lippincott Williams and Wilkins, pp 535–568. Bellhorn RW: Variation of canine distichiasis, J Am Vet Med Assoc 157:342–343, 1970. Bigelbach A: A combined tarsorrhaphy– canthoplasty technique for repair of entropion and ectropion, Veterinary and Comparative Ophthalmology 6:220–224, 1996.

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Blanchard GL, Keller WF: The rhomboid graftflap for the repair of extensive ocular adnexal defects, J Am Anim Hosp Assoc 12:576–580, 1976. Blaskovies L: Ectropion. In: Fox SA, editor: Ophthalmic Plastic Surgery, ed 4, New York, 1976, Grune and Stratton, pp 278–279. Brightman AH, Helper LC: Full thickness resection of the eyelid, J Am Anim Hosp Assoc 14:483–485, 1978. Carter JD: Combined operation for noncicatricial entropion, J Am Anim Hosp Assoc 8:53–58, 1972. Carter JD: Medial conjunctivoplasty for aberrant dermis of the Lhasa apso, J Am Anim Hosp Assoc 9:242–244, 1973. Chambers ED, Slatter DH: Cryotherapy (N2O) of canine distichiasis and trichiasis: an experimental and clinical report, J Small Anim Pract 25:647–659, 1984. Christmas RE: Common ocular problems of Shih Tzu dogs, Can Vet J 33:390–393, 1992. D’Anna N, Sapienza JP, Guandalini A, Guerriero A: Use of a dermal biopsy punch for removal of ectopic cilia in dogs: 19 cases, Vet Ophthalmol 10:65–67, 2007. Doherty MJ: A bridge-flap blepharorrhaphy method for eyelid reconstruction in a cat, J Am Anim Hosp Assoc 9:238–241, 1973. Dziezyc J, Millichamp NJ: Surgical correction of eyelid agenesis in a cat, J Am Anim Hosp Assoc 25:513–516, 1989.

Esson D: A modification of the Mustarde´ technique for the surgical repair of a large feline eyelid coloboma, Vet Ophthalmol 4:159–160, 2001. Gelatt KN: Resection of cilia-bearing tarsoconjunctiva for correction of canine distichia, J Am Vet Med Assoc 155:892–897, 1969. Gelatt KN, Blogg JR: Blepharoplastic procedures in small animals, J Am Anim Hosp Assoc 5:67–78, 1969. Grier RL, Brewer WG, Theilen GH: Hyperthermic treatment of superficial tumors in cats and dogs, J Am Vet Med Assoc 177:227–233, 1980. Gross SL: Surgery of the eyelids. In Bojrab MJ, editor: Current Techniques in Small Animal Surgery, Philadelphia, 1990, Lea and Febiger, pp 68–76. Grussendorf H: Outcome of a surgical technique for dogs suffering from macroblepharon, Munich, 2004, Transactions of the ECVO/ ESVO/DOK Meeting, 41. Gutbrod F, Tietz B: Entropion – operation mit Lidrandverku¨rzung, Vet Spiegel 4:14, 1993. Gwin RM: Selected blepharoplastic procedures of the canine eyelid, The Compendium 2:267–272, 1980. Halliwell WH: Surgical management of canine distichia, Am Vet Med Assoc 150:874–879, 1967.

Further reading Hamilton HL, Whitley RD, McLaughlin SA, Swaim SF: Basic blepharoplasty techniques, Compendium on Continuing Education for the Practicing Veterinarian 21:946–953, 1999. Helper LC, Magrane WG: Ectopic cilia of the canine eyelid, J Small Anim Pract 11:185–189, 1970. Jensen HE: Canthus closure, The Compendium 1:735–741, 1979. Johnson BW, Gerding PA, McLaughlin SA, Helper LC, Szajerski ME, Cormany KA: Nonsurgical correction of entropion in Shar Pei puppies, Vet Med 83:482–483, 1988. Kasa G, Kasa F: Exizionsraffung zur behebung eines entropiums beim chow-chow, Tierarztl Prax 7:341–349, 1979. Kirschner SE: Modified brow sling technique for upper lid entropion, Proceedings of the 25th Annual Meeting of the American College of Veterinary Ophthalmologists: Abstract 25:68, 1994. Krehbiel JD, Langham RF: Eyelid neoplasms of dogs, Am J Vet Res 36:115–119, 1975. Lawson DD: Canine distichiasis, J Small Anim Pract 14:469–478, 1973. Lenarduzzi RF: Management of eyelid problems in Chinese Shar-Pei puppies, Vet Med 78:548–550, 1983. Long RD: Treatment of distichiasis by conjunctival resection, J Small Anim Pract 32:146–148, 1991. McCallum P, Welser J: Coronal rhytidectomy in conjunction with deep plane walking sutures, modified Hotz–Celsus and lateral canthoplasty procedure in a dog, Vet Ophthalmol 5:376–379, 2004. McLaughlin SA, Whitley RD, Gilger BC, Wright JC, Lindley DM: Eyelid neoplasms in cats: a review of demographic data (1979 to 1989), J Am Anim Hosp Assoc 29:63–67, 1993. Miller WJ, Albert RA: Canine entropion, Compendium on Continuing Education for the Practicing Veterinarian 10:431–438, 1988. Moore CP: Eyelid and adnexal surgery from a practitioner’s perspective, North American Veterinary Conference Proceedings 14:556–559, 2000. Moore CP, Constantinescu GM: Surgery of the adnexa, Vet Clin North Am Small Anim Pract 27:1011–1066, 1997. Munger RJ, Carter JD: A further modification of the Kuhnt–Szymanowski procedure for correction of atonic ectropion in dogs, J Am Anim Hosp Assoc 20:651–656, 1984. Munger RJ, Gourley IM: Cross lid flap for repair of large upper eyelid defects, J Am Vet Med Assoc 178:45–48, 1981. Peiffer RL: Four-sided excision of canine eyelid neoplasms, Canine Practice 6:35–133, 1979. Peiffer RL, Gelatt KN, Gwin RM, Williams LW: Correction of inferior medial entropion as a cause of epiphora, Canine Practice 5:27–31, 1978. Pellicane CP, Meek LA, Brooks DE, Miller TR: Eyelid reconstruction in five dogs by the semicircular flap technique, Veterinary

and Comparative Ophthalmology 4:93–103, 1994. Read RA, Broun HC: Entropion correction in dogs and cats using a combination Hotz– Celsus and lateral eyelid wedge resection: results in 311 eyes, Vet Ophthalmol 10:6–11, 2007. Roberts SM, Severin GA, Lavach JD: Prevalence and treatment of palpebral neoplasms in the dog: 200 cases (1975–1983), J Am Vet Med Assoc 189:1355–1359, 1986. Roberts SR, Bistner SI: Surgical correction of eyelid agenesis in the feline. In Proceedings of the American Society of Veterinary Ophthalmologists, 1968, pp 18–21. Robertson BF, Roberts SM: Lateral canthus entropion in the dog, part 1: comparative anatomic studies, Veterinary and Comparative Ophthalmology 4:151–156, 1995. Robertson BF, Roberts SM: Lateral canthus entropion in the dog, part 2: surgical correction. Results and follow-up from 21 cases (1991–1994), Veterinary and Comparative Ophthalmology 5:162–169, 1995. Schmidt V: Kryochirurgische therapie der distichiasis des hundes Mh, Vet Med 35:711–712, 1980. Stades FC: A new method for surgical correction of upper eyelid trichiasis– entropion: operation method, J Am Anim Hosp Assoc 23:603–606, 1987. Stades FC: Reconstructive eyelid surgery, Tijdschr Diergeneeskd 112(Suppl 1): 585–635, 1987. Stades FC, Boeve MH: Surgical correction of upper eyelid trichiasis–entropion: results and follow-up in 55 eyes, J Am Anim Hosp Assoc 23:607–610, 1987. Stades FC, Gelatt KN: Diseases and surgery of the canine eyelids. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 563–617. Stades FC, Boeve´ MH, van der Woerdt A: Palpebral fissure length in the dog and cat, Progress in Veterinary and Comparative Ophthalmology 2:155–161, 1992. Stuhr CM, Stanz K, Murphy CJ, McAnulty J: Stellate rhytidectomy: superior entropion repair in a dog with excessive facial skin, J Am Anim Hosp Assoc 33:342–345, 1997. Van der Woerdt A: Adnexal surgery in dogs and cats, Vet Ophthalmol 7:284–290, 2004. Wheeler CA, Severin GA: Cryosurgical epilation for the treatment of distichiasis in the dog and cat, J Am Anim Hosp Assoc 20:877–884, 1984. Williams DL: Entropion correction by fornixbased suture placement: use of the Quickert–Rathbun technique in ten dogs, Vet Ophthalmol 7:343–347, 2004. Willis M, Martin C, Stiles J, Kirschner S: Brow suspension for treatment of ptosis and entropion in dogs with redundant facial skin folds, J Am Vet Med Assoc 214:660–662, 1999. Wyman M: Lateral canthoplasty, J Am Anim Hosp Assoc 7:196–201, 1971.

Wyman M: Ophthalmic surgery for the practitioner, Vet Clin North Am Small Anim Pract 9:311–348, 1979. Wyman M, Wilkie DA: New surgical procedure for entropion correction: tarsal pedicle technique, J Am Anim Hosp Assoc 24:345–349, 1988. Wyman M, Donovan EF, Rudy RL: Surgical correction of cicatricial ectropion in the dog, Southwestern Veterinarian 23:229–232, 1970.

Large animals and special species Allbaugh RA, Davidson HJ: Surgical correction of periocular fat pads and entropion in a potbellied pig (Sus scrofa), Vet Ophthalmol 12:115–118, 2009. Andrea CR, George LW: Surgical correction of periocular fad pad hypertrophy in potbellied pigs, Vet Surg 28:311–314, 1999. Baker JR, Leyland A: Histologic survey of tumors of the horse with particular reference to those of the skin, Vet Rec 96:419–422, 1975. Barnett KC: The eye of the newborn foal, J Reprod Fertil Suppl 23:701–703, 1969. Beard WL, Wilkie DA: Partial orbital rim resection, mesh skin expansion, and second intention healing combined with enucleation or exenteration for extensive periocular tumors in horses, Vet Ophthalmol 5:23–28, 2002. Bertone AL, McClure JJ: Therapy for sarcoids, Compendium on Continuing Education for the Practicing Veterinarian 12:262–265, 1990. Blanchard GL, Keller WF: The rhomboid graft flap for the repair of extensive ocular adnexal defects, J Am Anim Hosp Assoc 12:576–580, 1976. Blodi FC, Ramsey FK: Ocular tumors in domestic animals, Am J Ophthalmol 50:109–115, 1967. Brooks DE: Orbit. In Auer JA, Stick JA, editors: Equine Surgery, ed 3, St Louis, 2006, Saunders, pp 755–766. Brooks DE, Matthews AG: Equine ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2007, Blackwell, pp 1165–1274. Cotchin E: A general survey of tumors in the horse, Equine Vet J 9:16–21, 1977. Cutler N, Beard C: A method for partial and total upper lid reconstruction, Am J Ophthalmol 39:1–7, 1955. Diesem C: The organ of vision. In Getty R, editor: Sisson and Grossman’s Anatomy of Domestic Animals, ed 5, Philadelphia, 1975, WB Saunders, pp 226–244. Dugan SJ: Ocular neoplasia, Vet Clin North Am 8:609–626, 1992. Dugan SJ, Curtis CR, Roberts SM, Severin GA: Epidemiologic study of ocular/adnexal squamous cell carcinoma in horses, J Am Vet Med Assoc 198:251–256, 1991. Englis RV, Nassisse MP, Davidson MG: Carbon dioxide laser ablation for treatment of limbal squamous cell carcinoma in horses, J Am Vet Med Assoc 196:439–442, 1990.

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Farris H, Fraunfelder F: Cryosurgical treatment of ocular squamous cell carcinoma of cattle, J Am Vet Med Assoc 168:213–216, 1976. Fox LM, Thurmon JC: Bilateral ankyloblepharon congenital in a newborn foal, Vet Med Small Anim Clin 64:237, 1969. Gelatt KN: Blepharoplastic procedures in horses, J Am Vet Med Assoc 151:27–44, 1967. Gilger BC, Stoppini R: Diseases of the eyelids, conjunctiva, and nasolacrimal system. In Gilger BC, editor: Equine Ophthalmology, St Louis, 2005, Mosby, pp 107–156. Giuliano EA, MacDonald I, McCaw DI, et al: Photodynamic therapy for the treatment of periocular squamous cell carcinoma in horses: a pilot study, Vet Ophthalmol 11:27–34, 2008. Green LE, Berriatua E, Morgan KL: The prevalence and risk factors for congenital entropion in intensively reared lambs in south west England, Prev Vet Med 24:15–21, 1995. Grier RL, Brewer WG, Paul SR, Theilen GH: Treatment of bovine and equine ocular squamous cell carcinoma by radiofrequency hyperthermia, J Am Vet Med Assoc 177:55–61, 1980. Hamilton HL, Whitley RD, McLaughlin SA, Swaim SF: Basic blepharoplasty techniques, Compendium on Continuing Education for the Practicing Veterinarian 21:946–953, 1999. Hendrix DVH: Equine ocular squamous cell carcinoma, Clinical Techniques in Equine Practice 4:87–94, 2005. Kainer R, Stringer J, Lueker D: Hyperthermia for treatment of ocular squamous cell tumors in cattle, J Am Vet Med Assoc 176:356–360, 1980. Knottenbelt DC, Kelly DF: The diagnosis and treatment of periorbital sarcoid in the horse: 445 cases from 1974 to 1999, Vet Ophthalmol 3:169–191, 2000. Komaromy AM, Andrew SE, Brooks DE, Detrisac CJ, Gelatt KN: Periocular sarcoid in a horse, Vet Ophthalmol 7:141–146, 2004. Latimer CA: Diseases of the adnexa and conjunctiva. In Robinson NE, editor: Current Therapy in Equine Medicine, ed 2, Philadelphia, 1987, Saunders, pp 440–445. Lavach JD: The Handbook of Equine Ophthalmology, Fort Collins, Colorado, 1987, Gidding Studio, pp 63–97.

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Lavach JD: Large Animal Ophthalmology, St Louis, 1990, CV Mosby, pp 42–66. Lavach JD, Severin GA: Neoplasia of the equine eye, adnexa, and orbit: a review of 68 cases, J Am Vet Med Assoc 170:202–203, 1977. Lavach JD, Sullins K, Roberts S, Severin GA, et al: BCG treatment of periocular sarcoid, Equine Vet J 17:445–448, 1985. Linton LL, Collins BK: Entropion repair in a Vietnamese pot bellied pig, Journal of Small Exotic Animal Medicine 2:124–127, 1993. Martin CL: Ophthalmic disease in veterinary medicine, London, 2005, Manson, pp 145–182. McLaughlin SA, Whitley RD: Eyelid wounds. In Swaim SF, Henderson RA, editors: Small Animal Wound Management, ed 2, Baltimore, 1997, Williams and Wilkins, pp 403–430. Miller TR: Eyelids. In Auer JA, Stick JA, editors: Equine Surgery, ed 2, Philadelphia, 1999, WB Saunders, pp 450–464. Miller TR: Eyelids. In Auer JA, Stick JA, editors: Equine Surgery, ed 3, St Louis, 2006, Saunders, pp 702–715. Moore AS, Beam SL, Rassnick KM, Provost P: Long-term control of mucocutaneous squamous cell carcinoma and metastases in a horse using piroxicam, Equine Vet J 35:715–718, 2003. Moore CP, Whitley RD: Ophthalmic diseases of small domestic ruminants, Vet Clin North Am Large Anim Pract 6:641–665, 1984. Munger RJ, Gourley IM: Cross-lid flap for repair of large upper eyelid defects, J Am Vet Med Assoc 178:45–48, 1981. Peiffer RL, Williams R, Schenk M: Correction of congenital entropion in a foal, Vet Med Small Anim Clin 72:1219–1225, 1977. Plummer CE: Equine eyelid disease, Current Techniques in Equine Practice 4:95–105, 2005. Priester WA: Congenital ocular defects in cattle, horses, cats, and dogs, J Am Vet Med Assoc 160:1504–1511, 1972. Rasmussen RE: Repair of entropion in lambs, Mod Vet Pract 61:943–944, 1980. Riis RC: Equine ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology,

Philadelphia, 1981, Lea and Febiger, pp 569–605. Roberts SM: Ocular neoplasia. In Smith BP, editor: Large Animal Internal Medicine, ed 4, St Louis, 2009, Mosby, pp 1299–1305. Schwink K: Factors influencing morbidity and outcome of equine ocular squamous cell carcinoma, Equine Vet J 19:198–200, 1987. Severin GA: Severin’s Veterinary Ophthalmology Notes, ed 3, Fort Collins, 1996, Colorado State University Press, pp 200–207. Sundberg JP, Burnstein T, Page EH, et al: Neoplasms of equidae, J Am Vet Med Assoc 170:150–152, 1977. Theon AP, Pascoe JR: Iridium-192 interstitial brachytherapy for equine periocular tumours: treatment results and prognostic factors in 115 horses, Equine Vet J 27:117–121, 1995. Theon AP, Pascoe JR, Carlson GP, Krag DN: Intratumoral chemotherapy with cisplatin in oily emulsion in horses, J Am Vet Med Assoc 202:261–267, 1993. Townsend WM: Food and fiber-producing animal ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2007, Blackwell, pp 1275–1335. Walker M, Adams W, Hoskinson J, et al: Iridium-192 brachytherapy for equine sarcoid, one and two year remission rates, Veterinary Radiology 32:206–208, 1991. Welker B, Modransky PD, Hoffsis GF, Wyman MW, Rings DM, Hull BL: Excision of neoplasms of the bovine lower eyelid by H-blepharoplasty, Vet Surg 20:133–139, 1991. Whitley RD: Neonatal equine ophthalmology. In Koterba AM, Drummond WH, Kosch PC, editors: Equine Clinical Neonatology, Philadelphia, 1990, Lea and Febiger, pp 531–557. Whitley RD, Vygantas KR, Whitley EM: Ocular trauma. In Smith BP, editor: Large Animal Internal Medicine, ed 4, St Louis, 2009, Mosby, pp 1269–1274. Wyman M, Rings M, Tarr M, Alden C: Immunotherapy in equine sarcoid: a report of two cases, J Am Vet Med Assoc 171:449–451, 1997.

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Surgery of nasolacrimal apparatus and tear systems Kirk N. Gelatt

Chapter contents Introduction

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Nasolacrimal apparatus

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Nasolacrimal duct obstructions (extracorneal bullous spectaculopathy) in snakes

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Surgical procedures for the nasolacrimal apparatus

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SURGERY FOR KERATOCONJUNCTIVITIS SICCA

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ADAPTATIONS IN LARGE ANIMALS AND SPECIAL SPECIES

Surgical anatomy

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Introduction Diseases of the nasolacrimal and tear systems occur frequently in small animals and, to a lesser extent, horses. They can be grouped into those affecting the drainage apparatus, and those involving the tear-producing lacrimal gland and the superficial gland of the nictitating membrane. The health of the cornea, conjunctiva, and eyelids depends on continuous secretion of tears and removal by the drainage apparatus. Malfunctions by either or both tear-drainage and tear-producing systems can lead to overt acute-to-chronic diseases of the cornea, conjunctiva, and eyelids. Recent advances in the diagnosis and treatment of diseases of the nasolacrimal drainage and tear-producing systems in all animal species have resulted in markedly improved prognosis and successful clinical management of these patients. For convenience, the surgical procedures of the nasolacrimal and tear systems in this chapter are divided into surgical procedures that improve the drainage of tears, and those that increase or substitute for tear production. Diseases of the nasolacrimal apparatus that require surgical intervention are associated with partial-to-complete obstruction. Diseases of the lacrimal and tear-producing glands that require surgical management are usually associated with reduced levels of aqueous tear formation. With reduced levels of tear formation, disorders of the aqueous portion of the preocular or precorneal film develop, resulting in secondary corneal and conjunctival disease. Excessive lacrimation is usually secondary to pain, or external and internal ophthalmic diseases. Excessive tear secretion can exceed the normal capacity of the tear drainage system, thereby causing clinical signs of epiphora. Similarly,

a drainage system with disease also produces epiphora but tear production is at normal levels. Therapy of tear drainage system diseases is usually a combination of medical and surgical modalities, and re-establishment of patency.

Nasolacrimal apparatus The nasolacrimal drainage apparatus conveys tears and other debris from the external eye to the nasal cavity. This process appears to be only a passive capillary-like activity in animals, and the valve-like structures within the human nasolacrimal apparatus that prevent reverse flow have not been identified in small animals. The orbicularis oculi muscle may affect the lacrimal sac to create a vacuum and/or pressure that may assist in the movement of tears through the system. The anatomic arrangement of the orbicularis oculi muscle in the medial canthus and near the lacrimal sac also supports a more active process which may be involved in the uptake and movement of tears down the nasolacrimal apparatus. Two species possess only one lacrimal punctum: 1) the rabbit has a single ventral lacrimal punctum; and 2) the pig has a single upper lacrimal punctum (the ventral punctum and canaliculus are occluded and non-functional).

Nasolacrimal anatomy in dogs and cats The nasolacrimal apparatus consists of the upper and lower lacrimal puncta, the upper and lower canaliculi, the lacrimal sac, and the long nasolacrimal duct that empties into the rostral nasal cavity (Fig. 6.1). Although there are considerable

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Fig. 6.1 Latex preparations of normal nasolacrimal systems (metric scale shown). (a) Short-haired domestic cat. (b) Brachycephalic dog. (c) Dolichocephalic dog. (Reproduced with permission from Gelatt KN, Cure TH, Guffy MM, Jessen CL 1972 Dacryocystorhinography in the dog and cat. Journal of Small Animal Practice 13:381–397.)

variations in head shape and size in the different breeds of dogs, the predominant anatomic variation of the nasolacrimal apparatus is the variable length and diameter of the nasolacrimal duct. In dogs, the upper and lower lacrimal puncta are located in the palpebral conjunctiva just deep to the mucocutaneous junction, about 5 mm from the medial canthus, and appear as slit-like openings. In cats, the lacrimal puncta are more circular and smaller. From both lacrimal puncta the nasolacrimal system continues as two canaliculi that converge beneath the medial canthal ligament at the level of the lacrimal bone and fossa to form a poorly developed nasolacrimal sac. From the ventral portion of the lacrimal sac emerges the nasolacrimal duct to traverse the small intraosseous canal of the maxillary bone to enter the nasal cavity within the maxilloturbinate to the nasal meatus. This intraosseous portion of the nasolacrimal duct appears to have the smallest diameter, and appears to be the area most apt to become obstructed by inflammation and debris. The variable length of the nasolacrimal duct has a larger diameter, and may also have accessory openings immediately above the root of the upper canine teeth, perhaps just as it enters the nasal cavity. The distal opening of the nasolacrimal duct of both the dog and the cat can be located ventrolateral near the margin of the alar fold. Dilatation of the external nares by speculum assists in locating the distal opening. The distal opening can be cannulated for retrograde lavage of the nasolacrimal system. Because of the difficulty of retrograde nasolacrimal cannulation at the nares in the dog and cat, the convenient and readily accessible upper and lower lacrimal puncta are the usual entry for nasolacrimal flushes and other manipulations.

Nasolacrimal anatomy in large animals The anatomy of the nasolacrimal system of the horse and cow is very similar to that of the dog and cat, but much larger. In horses, the system starts as two lacrimal puncta, about 2 mm in diameter, located about 8 mm from the medial canthus and inside the lid margins. The two canaliculi or lacrimal canals connect the puncta with the lacrimal sac, which is poorly developed in the horse. The long and tortuous nasolacrimal duct, with a prominent dilatation above the first premolar tooth and about 25–30 cm long, extends from the lacrimal sac to the floor of the mucocutaneous junction of the nostril where its diameter is about 3–4 mm. From its beginning of about 6–7 mm diameter,

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it extends from the lacrimal sac through the osseous lacrimal canal of the maxillary bone (about 3–4 mm diameter). In mules, the nasolacrimal canal exits on the lateral part of the floor or lateral wall of the nostril. Accessory openings may also occur further caudad. In general, the primary clinical entry into the equine nasolacrimal system is into its distal orifice, at the beginning of the mucosa on the floor of the nostril. In cattle, the entire length of the nasolacrimal system is about 16–18 cm long. The upper and lower lacrimal puncta are 2–5 mm diameter and connected by the 1–1.5 cm diameter lacrimal canaliculi to the lacrimal sac (about 5–8 mm diameter). The nasolacrimal duct is about 12–15 cm long and straighter than the horse nasolacrimal duct. The distal orifice of cattle, which is not easily accessible clinically, is located near the lateral wall of the nostril on the medial surface of the alar fold of the ventral nasal concha. Hence, for nasolacrimal flushes in cattle, entry is usually through the upper or lower lacrimal punctum.

Clinical diagnostic tests for the nasolacrimal drainage apparatus The two most useful diagnostic tests for the determination of nasolacrimal apparatus functions in all animal species are: 1) the passage of topical fluorescein; and 2) the nasolacrimal flush and cannulation. The fluorescein test measures both the anatomic and physiologic patency of the nasolacrimal system. Aqueous fluorescein instilled onto the eye will normally enter the lacrimal puncta (mainly the lower punctum), traverse the entire nasolacrimal system, and appear at the external nares in 2–5 min. Fluorescein passage time seems directly related to the length of the entire nasolacrimal system. In brachycephalic breeds of dogs and cats, the nasolacrimal duct is considerably shorter and tortuous, and fluorescein may exit the nasolacrimal duct to enter the nasopharynx rather than the external nares. In any breed of dog, if the dog’s head is restrained upward during the test, the dye can also collect in the nasopharynx. With a delayed or negative fluorescein test, the entire nasolacrimal system can be flushed. The nasolacrimal flush tests for the anatomic patency of the nasolacrimal system. Under topical anesthesia and with the head of the dog firmly restrained, either the upper or lower lacrimal punctum is located, cannulated with a lacrimal or 20–22 g blunt stainless steel needle, and flushed with 1–3 mL of sterile saline. The saline should exit out of the external nares,

Surgical procedures for the nasolacrimal apparatus

unless the head is maintained dorsally, in which case the saline will enter the nasopharynx, and the animal may gag or sneeze. In the cat, topical anesthesia, sedation, and some magnification are generally necessary for nasolacrimal flushes. The cat’s lacrimal puncta are round rather than oval, and best cannulated with a 25–26 g blunt hypodermic needle or lacrimal cannula. In horses, the entire nasolacrimal system is flushed from its distal orifice, located on the floor of the nostril at its mucocutaneous junction. An 18 g blunt hypodermic needle connected via tubing and a 10 mL syringe is used to flush the system. Careful observation can usually distinguish the individual patency of the upper and lower lacrimal puncta during the injection of saline or sterile water. In cattle, nasolacrimal flushes are conducted under topical anesthesia and manual restraint of the animal’s head. Either the upper or lower lacrimal punctum is cannulated with an 18 g blunt hypodermic needle and a 10 mL syringe, and either saline or sterile water is used to flush the entire system. Visualization of the nasolacrimal system is possible in all animal species with dacryocystorhinography (Fig. 6.2). Observation of the system may be necessary when there is medically non-responsive or recurrent nasolacrimal sac or duct obstructions, or the possibility of nasal cavity masses. For dacryocystorhinography, general anesthesia of the patient and at least two radiographic views of the nasolacrimal system are necessary. A viscid cardiovascular radio-opaque solution (0.2–0.7 mL) is slowly injected into the upper lacrimal punctum in small animals and about 4–6 mL in foals and adult horses; 10–30 s later at least two radiographic views are taken. Dacryocystorhinography can detect irregularities in both the system’s diameter and course, and is generally most useful prior to consideration of surgeries of the lacrimal sac and nasolacrimal duct.

Nasolacrimal catheterization Nasolacrimal catheterization in the dog, cat, and horse consists of the placement of indwelling sutures or tubing spanning the upper or lower lacrimal punctum to the external nares for several days to a few months to help maintain patency. Nasolacrimal catheterization is indicated in patients with repeated obstructions of the nasolacrimal system (usually the nasolacrimal sac and duct), secondary to nasolacrimal duct atresia in foals, following lacerations of the upper nasolacrimal system (usually the lacrimal puncta

A

B

and canaliculi), and postoperatively after nasolacrimal system surgery. With the dog or cat under short-acting general anesthesia, a blunted (smooth melted end) 2-0 to 3-0 monofilament nylon suture is carefully inserted into the upper lacrimal punctum, upper canaliculus, lacrimal sac, and nasolacrimal duct to emerge from the external nares (Fig. 6.3a). The nylon suture can potentially become halted temporarily at the base of the lacrimal sac and at the accessory opening of the nasolacrimal duct immediately above the root of the upper canine tooth. Gentle turning and twisting of the suture can pass these barriers en route to the external nares. Once the nylon suture has traversed the system, PE 90 polyethylene, fine polyvinyl, or silicone tubing is slid over the entire length of the suture if a larger diameter cannula is preferred. The suture is removed leaving the tubing within the nasolacrimal system; both ends are attached by one or two simple interrupted non-absorbable sutures to the skin of the medial canthus and lateral of the external nares (Fig. 6.3b,c). In foals and adult horses, the entire nasolacrimal system from the upper or lower lacrimal punctum to its distal orifice can be easily traversed by a No. 5 French catheter. In some small animal patients only the nylon suture can be passed through the nasolacrimal system. Perhaps the lumen within the system is too restricted or swollen to permit passage of the larger diameter tubing. In these patients, the presence of the suture can still maintain the patency of the system. If the dog is lightly anesthetized, contact of the catheter in the distal nasolacrimal duct, perhaps at the accessory opening, may initiate sneezing. The system should remain in place for several days to a few weeks. Both topical solutions and systemic medications are usually administered with the nasolacrimal catheter in position. In general, an E-collar is necessary in small animals, or a face mask and stockinet in horses to prevent the animal from dislodging the ends of the nasolacrimal catheter. For sufficient and complete epithelialization of a new tear bypass, it is necessary for the catheter to remain in position for several weeks.

Surgical procedures for the nasolacrimal apparatus Surgical procedures for the nasolacrimal apparatus are divided into minor and major procedures. Minor procedures include surgical treatment of the imperforate punctum,

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Fig. 6.2 (a) Normal dacryocystorhinogram in the dog (lateral position): the canaliculi (A), nasolacrimal sac (B), and nasolacrimal duct (C). A secondary nasolacrimal orifice may be located immediately above the canine tooth (corner or third incisor). (b) Normal dacryocystorhinogram in the cat (lateral position). (c) Abnormal dacryocystorhinogram of a foal with atresia of the distal nasolacrimal duct (arrow). Note this ‘blind’ end of the nasolacrimal duct is considerably enlarged. (Reproduced with permission from Gelatt KN, Guffy MM, Boggess TS 1970 Radiographic contrast techniques for detecting orbital and nasolacrimal tumors in dogs. Journal of the American Veterinary Medical Association 156:741–746.)

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Fig. 6.3 Catheterization of the canine nasolacrimal system has both diagnostic and therapeutic advantages. Catheterization of the canine nasolacrimal system utilizes either a monofilament nylon suture or very small diameter silicone tubing. Both ends are sutured to adjacent skin. The system may remain in position for several weeks in ensure patency of the nasolacrimal system. (a) After deep sedation or short-acting general anesthesia, a 2-0 to 3-0 nylon suture is passed through the nasolacrimal system, starting at the dorsal lacrimal punctum. (b) Once the nylon suture has traversed the nasolacrimal system, 50 to 90 size polyethylene tubing is threaded down the suture. (c) Once completed, both ends of the tubing are transfixed to the adjacent skin by one or two simple interrupted non-absorbable sutures. An E-collar is recommended when the nasolacrimal catheterization is in place to prevent its dislodgement.

displacement of the lower punctum, enlargement of the lower punctum, lacerations of the canaliculi, and dacryocystotomy. The more extensive or major surgical procedures, which construct new avenues for the drainage of tears from the conjunctival fornix, include conjunctivorhinostomy, conjunctivomaxillary sinusotomy, and conjunctivoralostomy (or conjunctivobuccostomy). In the conjunctivorhinostomy technique, a tear drainage bypass is created into the caudal nasal cavity from the medial conjunctival fornix. In the conjunctivobuccostomy procedure, a subcutaneous tear drainage bypass is created from the middle of the ventral conjunctival fornix to terminate in the oral mucosa beneath the upper lip. These surgical procedures are indicated when the nasolacrimal system has been irreversibly damaged by inflammation, trauma, and neoplasia, and restoration of its patency is impossible in all animal species.

Surgery for imperforate lacrimal punctum Imperforate lacrimal punctum occurs in a number of breeds of dogs, but most frequently in the Toy and Miniature Poodles, Sealyham Terrier, American Cocker Spaniel, Golden Retriever, and Bedlington Terrier. Lower punctum obstructions are commonly presented because of epiphora. However, upper punctum obstructions do not generally produce clinical signs and are only detected as part of an ophthalmic examination. The imperforate lacrimal punctum should be distinguished from atresia of the puncta. In the imperforate lacrimal punctum, the opening of the punctum is covered by a thin veil of mucosa. Absence of the punctum indicates that the entire punctum is missing; with punctum absence the corresponding canaliculus is also missing. In my experience, imperforate lacrimal puncta are not infrequent in dogs, but atresia of the lacrimal puncta is rare. With the impaired drainage of tears with lower lacrimal punctum obstruction, excessive moisture and rust-colored staining of the medial canthal skin and hair are usually

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present (Fig. 6.4). Concurrent conjunctivitis is usually absent, but variable amounts of dermatitis of the eyelids and face may be present. Close inspection of the medial lower palpebral conjunctiva detects the absence of the lower lacrimal punctum. The topical fluorescein test is usually delayed or negative. The nasolacrimal flush performed through the upper lacrimal punctum exits from the nasolacrimal duct and external nares, but not through the lower punctum. Observation of the medial lower palpebral conjunctiva during the initial injection of saline may reveal a slightly raised or ballooned area during the initial flush that corresponds to the orifice of the lower punctum (Fig. 6.5a). The mucosa overlying the lower punctum may be excised, leaving an oval to round defect, or a cruciate incision may be performed in the area (Fig. 6.5b). The nasolacrimal flush is again performed to confirm patency. Topical antibiotic/ corticosteroid solutions are instilled six to eight times daily

Fig. 6.4 Young Miniature Poodle with unilateral imperforate lower lacrimal punctum. Note the epiphora and staining of the medial canthal hair.

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administered six to eight times daily to control the healing process and prevent fibrosis.

Displacement of the lower lacrimal punctum

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Fig. 6.5 With an imperforate lower lacrimal punctum, the upper lacrimal punctum is cannulated and flushed with sterile saline. (a) With the initial flush, the mucosa overlying the imperforate lacrimal punctum will bulge or tent, thereby indicating its position and the patency of the lower canaliculus. (b) Treatment of the imperforate lacrimal punctum is by excision of the mucosa over the lacrimal punctum orifice by small tenotomy scissors. Alternatively, the mucosa is incised in a cruciate manner. Topical antibiotics/ corticosteroids are instilled frequently for the next several days to maintain the lacrimal punctum orifice and to prevent the healing process from recovering the opening.

for 10–14 days to maintain patency and prevent the orifice wall from healing together. Intracanalicular gelatin implants may also be used to maintain the punctum’s patency.

Enlargement of the lower punctum Lower lacrimal micropuncta occur occasionally in the dog and result in epiphora. Scarring following conjunctival inflammation and trauma may also reduce the lower lacrimal punctum’s diameter and impair the drainage of tears. The fluorescein test will be delayed or negative. The nasolacrimal flush will indicate patency of the lower lacrimal punctum, but greater resistance to the flush. Treatment consists of surgical enlargement of the lower punctum. Under short-acting general anesthesia, the opening of the micropunctum is incised with the Bard–Parker No. 11 scalpel or Beaver No. 6500 or 6700 microsurgical blade (Fig. 6.6). The knife blade is slid further into the lower canaliculus, and an additional 3–5 mm of canaliculus wall is incised. Alternatively, the mucosa around the lower punctum is incised into three sections and excised. Postoperative treatment consists of topical antibiotics and corticosteroids

The lower punctum is normally situated 3–5 mm from the medial canthus and 1–2 mm bulbar of the eyelid margin in the palpebral conjunctiva. Displacement of the punctum occurs infrequently in the dog; in these patients the lower punctum is usually displaced several millimeters ventral of its normal position. The condition may be primary or secondary to entropion, ectropion, trauma, and scarring. Treatment for a displaced lower punctum is influenced by the extent and severity of epiphora, the associated dermatitis, and tear staining. Mild or intermittent epiphora is usually tolerated, and no surgical treatment is attempted. Patients with extensive medial canthal dermatitis and irritation require treatment. The fluorescein passage test is either delayed or negative. The nasolacrimal flush will indicate if the system is patent, but the lower punctum is failing to convey the normal volume of tears into the lower canaliculus. The recommended initial treatment is to dilate the displaced lower punctum and canaliculus to enhance the uptake of the tears. In the event that this fails, the displaced punctum can be relocated to its normal position or a new exit for tear drainage is constructed to the mouth, maxillary sinus, or nasal cavity. Transposition of the lower punctum, although minor surgery, requires magnification and cannulation of the punctum and canaliculus during surgery and for several weeks postoperatively. After general anesthesia and surgical preparation of the medial canthus, the lower punctum and canaliculus are cannulated with 2-0 to 3-0 monofilament nylon, and PE 90 polyethylene tubing is slid over the suture. The mucosa around the lower punctum is incised with the Beaver No. 6400 microsurgical blade. By dissection with tenotomy scissors, the lower canaliculus is isolated for approximately 5–8 mm. The lower punctum and canaliculus are moved to a small linear incision in the lower palpebral conjunctival mucosa, 1–2 mm deep in the eyelid margin. The monofilament suture or polyethylene tubing catheter is sutured to the medial lower eyelid and the skin caudal to the nostril. If the transplanted lacrimal punctum and canaliculus have some surrounding mucosa, at least three 6-0 simple interrupted absorbable sutures are placed about the punctum to secure it. If limited mucosa is available, sutures may adversely affect the punctum, and the cannula is critical to maintain the transplanted tissues in position. Topical antibiotics and corticosteroids as well as systemic antibiotics are administered for 7–10 days. The nasolacrimal catheter is removed after 3–4 weeks.

Lacerations of the canaliculi Fig. 6.6 Lower lacrimal micropunctum is associated with epiphora, but a patent nasolacrimal flush. The small size of the lower lacrimal punctum prevents the normal volume of tears entering the nasolacrimal system, and hence, the epiphora. Treatment of lower lacrimal micropunctum consists of enlargement of the orifice, beginning at the lower canaliculus with a 3–5 mm linear incision with the Bard–Parker No. 11 or Beaver No. 6500 blade. Alternatively, the periphery of the lower punctum orifice is incised into three sections and partially excised.

Most lacerations of the dog’s eyelids involve the lateral aspects; medial eyelid lacerations are infrequent. If the laceration affects the medial canthus, transection of the canaliculus is likely. Lacerations that involve the canaliculi, generally the lower, are usually in the vertical or somewhat angled plane. The torn eyelid is usually highly edematous; debris and hemorrhage may obscure the extent of the injury.

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Identification of the canaliculus is usually difficult but is enhanced during the injection of air either retrogradely from the nares or from the fellow nasolacrimal punctum. The exit of bubbles from within the lacerated lid can greatly facilitate localization and canalization of the severed canaliculus. Tissue destruction and resultant inflammation can markedly distort the area. After surgical preparation, the upper lacrimal punctum and canaliculus are cannulated with the gold lacrimal or 22–23 g stainless steel needle, and the system is flushed to locate the lower canaliculus. The distal portion of the lacerated lower canaliculus is usually difficult to locate because of tissue trauma and swelling. If both parts of the canaliculus can be identified and cannulated, the edges of the eyelid laceration are carefully apposed, usually in two layers. The nasolacrimal catheter of PE 50 to 90 polyethylene is manipulated over the suture through the system, tied, and sutured to the skin at the medial canthus and lateral to the nostril. Postoperative treatment includes topical and systemic antibiotics and corticosteroids. The nasolacrimal catheter is left in situ for 4–6 weeks. Frequency of topical therapy should be about six times daily. After most of the eyelid swelling has decreased, topical therapy is applied three to four times daily until the nasolacrimal catheter is removed.

Dacryocystotomy Surgical procedures of the canine and feline lacrimal sac are infrequent, as the sac is poorly developed, partially covered by the lacrimal bone, and caudal of the medial aspects of the orbicularis oculi muscle. Dacryocystitis is not infrequent in the dog. Foreign bodies, bacterial infections, and obstruction of the lacrimal sac characterize dacryocystitis. Occasionally a fistula may develop from the lacrimal sac onto the skin of the medial canthus (Fig. 6.7). Dacryocystitis usually responds to a combination of nasolacrimal flushes and antibiotic therapy. For recurrent dacryocystitis, nasolacrimal catheterization is recommended. In those patients that do not respond to these treatments, an exploratory dacryocystotomy for foreign bodies is recommended. The fluorescein passage test is usually negative; if a fistula is present, the dye may exit its distal opening. The nasolacrimal flush, normally through the upper lacrimal punctum,

Fig. 6.7 A dog with chronic dacryocystitis. Note the swelling of the medial lower eyelid and a fistula extending from the nasolacrimal sac onto the skin.

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usually indicates whether the system is plugged; if a fistula is present, the flush may exit this route. When additional pressure is applied during flushing, purulent material will often exit from the lower lacrimal punctum. Once the saline flush emerges freely from the lower lacrimal punctum, digital pressure is applied to the lower lacrimal punctum to redirect the flush through the lacrimal sac and nasolacrimal duct. Additional purulent exudates may emerge from the external nares. Fortunately, most nasolacrimal foreign bodies lodge in the lower canaliculus or nasolacrimal sac, and are expelled by nasolacrimal flushes from the upper lacrimal punctum. Occasionally a small serrated or 1  2 teeth Bishop–Harmon forceps is necessary to extract the foreign body. Post-flushing treatment is directed at combating infection, reducing inflammation, and maintaining patency. Broadspectrum antibiotics are administered topically and parenterally. Choice of antibiotics may also be altered by sensitivity tests. Most bacteria isolated from dacryocystitis in dogs are similar to those recovered from conjunctivitis, and include hemolytic and non-hemolytic Staphylococcus spp., Escherichia coli, Enterobacter spp., and alpha-hemolytic streptococci. Antibiotics in aqueous and non-irritating solutions can also be added to sterile saline during the nasolacrimal flush. Corticosteroids are infrequently used, but if the swelling is severe and the results of sensitivity tests guide the choice of antibiotics, anti-inflammatory agents may be helpful. To maintain nasolacrimal patency, either repeated nasolacrimal flushes or catheterization of the system may be necessary. In dacryocystotomy, the medial canthal and ventromedial lower eyelid regions are prepared for aseptic surgery. A PE 50 to 90 polyethylene catheter is inserted through either the lower or upper lacrimal punctum into the lacrimal sac. This catheter must be maintained in position to locate the lacrimal sac, and preserve the integrity of the cannulated lacrimal punctum and associated canaliculus. The lacrimal sac is located in a fossa in the lacrimal and frontal bones, posterior to the lacrimal crest (Fig. 6.8). A 2–3 cm skin incision is made parallel to the lower eyelid

Fig. 6.8 The nasolacrimal sac is located in a fossa in the lacrimal and frontal bones (arrow), posterior to the lacrimal crest. As the nasolacrimal sac is not well developed in the dog, a polyethylene catheter inserted into the lower lacrimal punctum, lower canaliculus, and into the nasolacrimal sac facilitates its location.

Surgical procedures for the nasolacrimal apparatus

margin along the ventromedial orbital rim. By blunt–sharp dissection, the subcutaneous and periorbital tissues are penetrated to reach the lacrimal bone. The nasolacrimal catheter can be palpated as it enters the lacrimal sac within the lacrimal fossa, about 5 mm ventral of the orbital rim. A 3 mm bone burr is used to drill a hole in the lacrimal bone and into the lacrimal sac. Once the lacrimal sac is entered, flushing from the nasolacrimal catheter will enter the freshly drilled hole. Any foreign body and other material can be removed from the lacrimal sac. Closure consists of 4-0 simple interrupted absorbable sutures of the periosteum of the lacrimal bone, the periorbita, and the subcutaneous layer of the eyelid. Skin apposition is by 4-0 simple interrupted non-absorbable sutures. The nasolacrimal catheter is retained in the system for 14– 21 days to maintain patency as the nasolacrimal sac wall is not apposed by sutures, and to ensure delivery of topical antibiotics to the area. Systemic antibiotics are also recommended because contamination of the surgical site occurs once the lacrimal sac is opened and irrigated.

Conjunctivorhinostomy (caudal nasal cavity) With congenital and acquired loss of the different parts of the nasolacrimal system, an alternative route can be constructed surgically to prevent epiphora and to drain the tears directly into the nose or oral cavity. The continuous presence of tears at the medial canthus and adjacent skin frequently results in medically uncontrollable chronic dermatitis, rust-colored changes in the hair, and pruritus. Alternative routes that can be constructed surgically in small animals for the tears to exit the ventral conjunctival fornix include the caudal nasal cavity, the maxillary sinus, and the mouth (Fig. 6.9). Fortunately, atresia of the distal nasolacrimal duct in young horses is usually within the area of the nostril, and can be reached through the nostril. In conjunctivorhinostomy, a permanent fistula is constructed surgically to extend from the medioventral conjunctival fornix to the nasal cavity or maxillary sinus (often termed conjunctival maxillary sinusotomy). Over time, this

Fig. 6.9 When the nasolacrimal system has been permanently damaged, alternative routes for exit of the tears can be constructed surgically to enter the posterior nasal cavity or maxillary sinus (conjunctivorhinostomy), or the mouth (conjunctivobuccostomy). The approximate sites for entry into the caudal nasal cavity (A) and maxillary sinus (B) are depicted on the canine skull.

surgical fistula is eventually lined with mucous membrane while its patency is maintained by an indwelling catheter. Polyethylene (3 mm outside diameter) or silicone tubing can be constructed to fit in the fistula, and maintain patency during healing. Polyethylene tubing is more rigid and when exposed to heat will flare to form an 8  1.4 mm flange which can be attached by sutures to adjacent tissues. Silicone tubing is more flexible, but sometimes cannot be manipulated into confined areas without buckling. To add a flange to the silicone tubing, special silicone glue is necessary to attach the silicone sheeting fashioned into any shape and size. For this procedure, the stiffer polyethylene tubing is clearly superior. The polyethylene tubing (40 mm long), with the heat-produced flange on its proximal end and a beveled end, protrudes into the nasal cavity. Premature loss of the indwelling catheter and its non-replacement will usually result in closure of the surgical fistula and failure of the surgery. After surgical preparation of the medial canthal region, an incision is made in the area of the caruncle at the base of the nictitating membrane. With blunt dissection of the ventromedial orbital rim periorbita, the periosteum is isolated for approximately 3–4 mm. The periosteum and maxillary bone are incised with either a trephine or progressively larger Steinmann pins to enter the nasal cavity. Entry into the nose usually produces variable amounts of hemorrhage. After the tract has been flushed and cleared of debris, a 40 mm length of polyethylene tubing, positioned about the malleable probe, is manipulated into position. If the tubing tends to protrude after placement, it is probably in contact with the nasal floor or medial septum and should be shortened. At least three non-absorbable sutures are used to anchor the proximal end of the tubing to the conjunctival mucosa and medial canthus. After anchoring of the indwelling catheter, a final flush with sterile saline should indicate its patency and position within the posterior nasal cavity. Postoperative therapy consists of topical and systemic antibiotics and topical corticosteroids for 5–7 days. An E-collar, while annoying, is valuable to maintain the catheter in place for as long as possible. The tubing should remain in situ for at least 2 months to permit epithelialization of the fistula. Topical antibiotics once or twice daily are useful. If the tubing becomes plugged, flushing with 0.9% sterile saline solution is used to re-establish patency. Possible complications after this procedure include tube displacement and loss, closure of the fistula, mucous membrane overgrowth, and increased epiphora. The success rate of this method is 85–90%. Maintenance of the tubing during the time of permanent fistulization is critical; premature loss of the tubing generally requires placement of another as soon as possible and before the fistula heals closed. Conjunctivorhinostomy is less successful in cats as the fistulas tend to close eventually. The indwelling catheter should be left in the cat for as long as possible.

Conjunctival maxillary sinusotomy (into the maxillary sinus) Another method developed for the dog constructs a buccal mucosa tunnel that extends from the medial lower conjunctival fornix through the subcutaneous tissues and the

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maxilla to enter the maxillary sinus. Patency of the buccal tunnel is maintained by 4 cm long indwelling polyethylene tubing (PE 50 to 90) for several weeks. The buccal mucosa tunnel is constructed from a freshly harvested 15  20 mm section of buccal mucosa. A polyethylene tube is threaded through its lumen to maintain its shape and facilitate handling. After surgical preparation of the lower eyelid and area over the maxillary sinus, a skin incision is made 1 cm lateral of the medial canthus for 3 cm to the area over the maxillary sinus. Once over the maxillary sinus, the periosteum is reflected and an 8–10 mm trephine is used to enter the maxillary sinus. The buccal tunnel is positioned between the conjunctival fornix and maxillary sinus, and its ends secured. Simple interrupted absorbable sutures are used to attach the proximal buccal tunnel to the conjunctival mucosa and submucosa, and the distal end of the tunnel to the maxillary sinus mucosa and periosteum. The skin incision is apposed with simple interrupted non-absorbable sutures. Postoperative management after this method is identical to the earlier procedure. Maintenance of the indwelling catheter within the buccal tunnel for several weeks is critical for its success.

Conjunctivobuccostomy An alternative to conjunctivorhinostomy, conjunctivobuccostomy is technically easier because the facial bones are not involved. In this procedure, a subcutaneous tunnel is constructed from the middle part of the lower conjunctival fornix to the upper fornix of the upper lip (Fig. 6.10). A buccal mucosa tunnel can be constructed and positioned between the two fornices. A long-term indwelling catheter of polyethylene tubing must also be constructed and maintained within the subcutaneous buccal tunnel to maintain patency as the surgical bypass epithelializes. An alternative method is to insert a long-term indwelling polyethylene catheter, anchored securely in the conjunctival and buccal fornices, and allow for epithelialization to occur. Postoperative management is identical to the two previous procedures.

ADAPTATIONS IN LARGE ANIMALS AND SPECIAL SPECIES

Nasolacrimal obstructions in large animals Nasolacrimal obstructions are in frequent in horses. In foals and young horses, atresia of the distal nasolacrimal duct and nasal punctum manifests as epiphora, chronic reflex conjunctivitis, and a prominent bulge in the distal nasolacrimal canal, fortunately accessible through the nostril. Other surgically treated diseases are lacrimal punctum atresia, and more generalized nasolacrimal duct agenesis. Dacryocystitis is infrequent in adult horses, and is usually associated with chronic obstruction and bacterial infection of the lacrimal sac and chronic reflux conjunctivitis. Dacryocystorhinography is an excellent diagnostic procedure for nasolacrimal obstruction in horses and cattle.

Distal nasolacrimal duct atresia in foals and young horses This surgery can be performed in the sedated and standing foal, but may involve less time if general anesthesia is used. The bulging area of the distal nasolacrimal duct (basically a blind pouch) is cleaned with surgical soap and rinsed with 0.5% povidone–iodine (Fig. 6.11a). The entire nasolacrimal system is catheterized through the upper lacrimal punctum with silicone tubing, polyethylene tubing, or a No. 40 French catheter so that the catheter tip can be palpated in the ‘blind’ pouch. The top of bulge is incised by scalpel; considerable hemorrhage may result and is controlled by surgical sponges and direct pressure. The wound is left open to heal with the catheter in position to ensure patency. Both ends of the catheter are secured by non-absorbable sutures to the medial canthus and upper nostril respectively (Fig. 6.11b). The entire area is covered by stockinet and a mask with a hard cup to reduce rubbing and protect the indwelling catheter for several weeks. Topical antibiotics/ corticosteroids are administered daily for several days. In absence of the lower nasolacrimal system, canaliculorhinostomy can be performed in the horse.

Nasolacrimal duct obstructions in cattle

A Fig. 6.10 In conjunctivobuccostomy the tears drain from the lower conjunctival fornix through a subcutaneous fistula into the mouth. (a) A subcutaneous tunnel of buccal mucosa is constructed to span the ventral conjunctival fornix to the dorsocaudal buccal area. (b) To maintain patency of this new buccal mucosa tunnel, a custom-constructed polyethylene tubing is left in situ for several weeks as shown in this immediate postoperative appearance after conjunctivorhinostomy in a cat. The silicone tubing has been inserted in the new surgical fistula into the nasal cavity, and must remain in position for several weeks for epithelialization of the fistula.

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Nasolacrimal obstructions are rare in cattle. Dacryocystorhinography should precede any surgery for either the lacrimal sac or nasolacrimal duct in cattle. Conjunctivorhinostomy has been reported in cattle, providing passage for tears from the front of the caruncle through the lacrimal bone and ventral nasal concha into the ventral nasal meatus. A section of polyethylene urinary catheter is positioned within the fistula (ends are secured to the medial canthus and nostril) and maintained for several weeks.

Nasolacrimal duct obstructions (extracorneal bullous spectaculopathy) in snakes In snakes and certain lizards the cornea is protected by a transparent spectacle formed by fusion of the eyelids during embryonic development. The tears, formed by the

Nasolacrimal duct obstructions (extracorneal bullous spectaculopathy) in snakes

Fig. 6.11 Atresia of the nasolacrimal duct in the foal. (a) The blind end of the distal nasolacrimal duct is usually visible and accessible just caudal of the mucocutaneous junction on the floor of the nostril. (b) After a simple incision of the top of this ‘blind end’ of the nasolacrimal duct, silicone or polyethylene tubing is positioned within the entire nasolacrimal system for several weeks to maintain the healing distal orifice patent, and secured by skin sutures at both ends or simply tied together. A stockinet is placed over the face to prevent dislodgement of the catheter until removal.

Harderian gland, enter the subspectacular and precorneal space to drain via the lacrimal duct into the mouth or the duct of Jacobson’s organ within the mouth. Obstruction of the lacrimal duct, usually at the level of the roof of the mouth, results in accumulation of tears with enlargement of the subspectacular space and swelling of the spectacle that mimics enlargement of the eye and glaucoma (pseudobuphthalmos). Development of the lacrimal duct occlusion and distention of the spectacle is usually acute. Occlusion of the lacrimal duct usually results from pressure or scarring from tumors and granulomas, and oral lesions, usually grouped together as ulcerative and/or necrotic stomatitis, and inflammations of Jacobson’s organ (Fig. 6.12). With obstruction of the lacrimal duct and ascending infections from the mouth, a septic process can develop within the subspectacular space. Pseudomonas spp., Proteus spp., and

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Providencia rettgeri, commonly isolated from oral infections, can also be recovered from the subspectacular fluids. Flagellates can also be recovered; their role in the development of subspectacular infection is unknown. With subspectacular infections, the spectacle loses its clarity, and may develop ulcerations and bullae. Fluorescein can be injected carefully into the subspectacular space to demonstrate patency or obstruction of the lacrimal drainage apparatus. Treatment of the condition is essential to prevent infection of the cornea and intraocular tissues, and damage to the spectacle. The subspectacular space can be aspirated and injected with low concentrations of antibiotics. In severe cases, a significant section of the spectacle has been excised, but the exposed cornea must be medicated daily with ophthalmic antibiotic ointments until the next shedding of the skin or ecdysis occurs.

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Fig. 6.12 Nasolacrimal (lacrimal) duct obstructions (a) and ascending oral infections (b) in snakes are characterized by enlargement of the subspectacular space with tears and inflammatory debris and swelling of the spectacle as well as the oral infection. Initial treatment consists of aspiration and culture and cytology of the subspectacular fluids, and treatment of any infections. (c) Sometimes partial removal of the spectacle is also necessary.

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Another effective method is excision of a small 30 wedge of the ventral spectacle that permits sampling of the tears for possible pathogens, and an entry for repeated flushing and treatment of the condition. With the next shedding, the spectacle integrity will be restored. Examination of the mouth and treatment of ulcerative and necrotic stomatitis with parenteral systemic antibiotics are also indicated to prevent recurrence of the lacrimal duct obstruction. Conjunctivoralostomy has also been performed in snakes, using a curved 18 g hypodermic needle to create a fistula between the inferior fornix of the subspectacular space and the roof of the mouth. Patency during healing is maintained by a catheter 0.635 mm in diameter sutured to the roof of the mouth and ventral periocular scales with 5-0 sutures (absorbable in the mouth and silk for the skin). Because of the importance of Pseudomonas species in oral infections and infected subspectacular tissues in snakes, systemic and topical gentamicin are administered postoperatively.

SURGERY FOR KERATOCONJUNCTIVITIS SICCA Diseases of the tear-secreting glands are demonstrated by reduction in tear production, changes in the preocular (precorneal) film, and secondary keratoconjunctivitis. Tears are composite secretions with oily, aqueous, and mucoid portions. The lacrimal gland, the superficial gland of the nictitating membrane, and any accessory lacrimal glands within the conjunctiva produce tears. In the dog, excision of either the lacrimal or the nictitans gland does not result in clinical disease, i.e., keratoconjunctivitis sicca (KCS), or significant changes in the Schirmer tear test 1. However, the Schirmer tear test 2, conducted under topical anesthesia, indicates a lower level of basal tear production. In dogs, the surgical loss of both glands results in keratoconjunctivitis sicca. Surgical studies in the dog suggest that the lacrimal gland provides about 60–75% of the total tears, and the superficial gland of the nictitating membrane 25–40%. Diseases of the nictitating membrane tear gland, such as ‘cherry eye’ or a prolapsed and inflamed gland, can predispose the same eye to keratoconjunctivitis sicca at a later time (even if treated successfully by surgical replacement of the gland). Keratoconjunctivitis sicca occurs most frequently in the dog; it is infrequent in cats, and is rare in horses and cattle.

Surgical anatomy Tear production in animals results primarily from two glands. The lacrimal gland is located in the periorbital fascia dorsolateral to the globe and immediately beneath the lateral orbital ligament and zygomatic arch in the dog and cat. The superficial gland of the nictitating membrane is the smaller tear-producing gland, and surrounds the lower aspects of the base of the cartilage of the third eyelid. While the tears from the lacrimal gland flow ventral and medial to the nasolacrimal drainage apparatus, the tears produced by the superficial gland of the nictitans are probably mixed and distributed across the cornea and conjunctiva by a combination of movements by the nictitating membrane and upper eyelid. Movements of the lower eyelid are limited, and it appears that the lower eyelid and conjunctival fornix mainly

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serve as the collecting ‘pool’ for the tears en route to the ventromedial conjunctival fornix and the lower lacrimal punctum. In humans, accessory tear glands within the conjunctiva, the glands of Krause and Wolfring, have not been identified in animals, and may have been consolidated through evolution into the single gland of the nictitating membrane. Both the lacrimal gland and superficial gland of the nictitating membrane have considerable cholinergic and adrenergic nerve endings. The adrenergic nerve endings are associated with the blood vessels and are probably involved in local regulation of blood flow. The cholinergic nerve endings are mainly around the acini in both glands. Experimental electrical stimulation of the lacrimal nerve in cats results in marked increases in the rate of tear formation. The superficial gland of the nictitating membrane in the dog may be the analog for the accessory lacrimal glands in humans. Studies in the dog suggest that tear production may differ from that of humans in that both tear glands appear to contribute to the basal and reflex portions of tear formation. The lacrimal gland contributes about 60–75% of the total tear volume; the superficial gland of the nictitating membrane contributes 25–40%. As a reasonable substitute for tears, saliva from the parotid gland is well tolerated by the cornea and conjunctival surfaces in humans, dogs, cats, and horses. Parotid secretions are continuous, but of much larger quantities during eating. The parotid gland is located caudal to the mandible with its duct emerging from its base. The origin of the parotid duct consists of several small ducts that converge to form one large duct at the base of the gland and a single duct that passes forward external to the masseter muscle. The parotid duct is closely attached to the external masseter fascia, and separation of the two structures during surgery is sometimes quite tedious. In most breeds of dogs the course of the parotid duct is straight from the base of the parotid salivary gland to its papilla. However, in brachycephalic breeds, the course of the parotid duct is less predictable, and often tends to be quite ventral of its usual straight course. The parotid duct is medial to and between the dorsal and ventral buccal divisions of the facial nerve in the dog (Fig. 6.13). The duct usually appears pink–white, whereas the nerve branches are white. Cannulation of the parotid duct with either green or blue monofilament nylon greatly aids in its identification and prevents confusion with either of the dorsal and ventral buccal nerves during surgery. The parotid duct terminates in a papilla located immediately caudolateral to the carnassial tooth. In this area the buccal nerves and facial vein usually have multiple branches that complicate the final phase of parotid duct dissection. The parotid duct often extends 0.5–1 cm submucosally before it enters the papilla. The papilla of the parotid duct should not be confused with the one or more papillae of the zygomatic salivary gland in the dog. The anatomy of the parotid gland and duct in the cat is very similar to the dog but smaller (Fig. 6.14). The papilla of the parotid duct enters the cat’s mouth immediately adjacent to the last premolar tooth. The parotid duct can be cannulated with 4-0 monofilament nylon in cats. The dorsal and ventral buccal nerves are more distant to the parotid duct, but converge just before the anterior facial vein and before the duct terminates in its papilla.

Surgical anatomy

Surgical treatment of acute keratoconjunctivitis sicca (KCS) The treatment of acute KCS includes medical or surgical management, or a combination of both, and should be considered an ophthalmic emergency. Medical therapy of acute KCS includes topical tear substitutes as well as stimulation of existing tear formation to increase moisture to the external eye. Antibiotics are administered to suppress or eliminate opportunistic bacteria. Surgical procedures for acute KCS include bulbar and palpebral conjunctival grafts as well as nictitating membrane flaps to manage the rapid and often progressive corneal ulceration of acute KCS. These surgical procedures will be presented in Chapter 7.

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Fig. 6.13 The major anatomic landmarks and surgical considerations for parotid duct transposition in the dog from the original drawing by Lavignette (1966). During surgical dissection of the parotid duct (1), the facial vein (2), the dorsal buccal nerve (3), and the ventral buccal nerve (4) should be identified. A skin biopsy punch or corneal trephine is used to incise the parotid duct papilla in the mouth (5). A small hemostat is inserted through the ventrolateral conjunctival fornix and a subcutaneous tunnel to pull the parotid duct into the fornix for apposition. (Reproduced with permission from Lavingnette AN: 1966 Keratoconjunctivitis sicca in a dog treated by transposition of the parotid salivary duct. Journal of the American Veterinary Medical Association 148: 778–786.)

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Fig. 6.14 Surgical anatomy for parotid duct transposition in the cat. As in the dog, the feline parotid duct (A) traverses anteriorly external to the masseter muscle and between the dorsal (B) and ventral (C) buccal nerves. As the distal end of the duct and papilla are approached, several small branches of the facial vein are encountered. (Reproduced with permission from Gwin RM, Gelatt KN, Peiffer RL 1977 Parotid duct transposition in the cat with keratoconjunctivitis sicca. Journal of the American Animal Hospital Association 13:42–45.)

Surgical treatment of medically nonresponsive chronic keratoconjunctivitis sicca by parotid duct transposition in dogs and cats In those patients that have failed to respond to medical treatment for chronic KCS, parotid duct transposition to substitute saliva for tears is recommended (Fig. 6.15). Trial medical therapy with topical cyclosporin A twice daily should span at least 2–3 months with repeated monitoring with the Schirmer tear test to detect any improvement in tear secretion. Topical treatment with antibiotics and corticosteroids is also continued during this time. Surgical or electrocautery ablation of the lower lacrimal punctum or insertion of lower punctal occluders in the dog to conserve existing tears has not been successful because the level of tear production is too low. Reduction in the size of the palpebral fissure with lateral canthoplasty, partial permanent tarsorrhaphy, or other methods to conserve the existing moisture have not been useful in the dog because most KCS patients have little, if any, tear production. The dog and cat must be evaluated for parotid function before surgery. The gland and duct should be palpated for abnormalities. The papilla of the parotid duct immediately adjacent to the caudal aspect of the carnassial tooth should be inspected, and saliva flow should be observed. Parotid gland function can be tested by applying a few drops of 1% atropine ophthalmic solution to the patient’s tongue. Profuse salivation should follow, associated with the bitter taste of atropine.

Fig. 6.15 Chronic keratoconjunctivitis sicca in an American Cocker Spaniel. The eye is characterized by a completely pigmented cornea and copious mucopurulent conjunctival exudates. The condition, not respondent to either long-term topical cyclosporin A or oral pilocarpine, is recommended for parotid duct transposition.

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Parotid secretion has many similarities to tears and is nonirritating to the eye. Canine KCS patients with parotid duct transpositions lasting over 7 years have not exhibited corneal irritation to parotid secretions. Parotid duct transposition was first reported in experimental dogs in 1959 in Japan; the first description of this procedure for the management of canine KCS was in 1966. Since then, several veterinary investigators have reported slight modifications of the original surgical procedure, postoperative results, and complications. Parotid duct transposition can also be performed in cats, using the same surgical procedure and clinical management.

Surgical procedure The parotid duct can be approached by either the oral or lateral route. The lateral approach is preferred because of better exposure, less potential for transection of the duct, and septic contamination of the incision from the mouth is markedly reduced. The oral approach was developed initially in humans to avoid any facial skin incision and resultant scar. After general anesthesia and surgical preparation of the eyelids and lateral face, the papilla of the parotid duct is identified near the base (ventrolateral) of the upper carnassial tooth. Care must be taken not to confuse it with the papillae of the ducts of the zygomatic salivary gland, which open near the gingival border above the last molar tooth. A 2-0 to 3-0 monofilament nylon suture, with the tip flamed to ‘blunt’ it, is passed into the parotid duct papilla. The suture can often be observed and felt moving beneath the skin as it passes caudally in the parotid duct to the gland. Two methods have been used to incise the papilla and rostral parotid duct. The mucosa can be incised and a round to oval portion of mucosa removed with the papilla. With this method, dissection can be difficult and excessive buccal mucosa may be excised. An alternative oral approach using a 6 mm biopsy punch or corneal trephine is recommended (Fig. 6.16a). After the mucosal incision around the parotid duct papilla and placement of the suture cannula, a 0.5% povidone–iodine soaked gauze sponge is positioned in the mouth to provide at least some disinfection in the area. After draping of the area directly over the entire length of the parotid duct and the eye, the position of the nylon suture in the duct is again palpated through the skin. A skin incision is made along the duct through the skin and superficial facial muscles to expose the duct (Fig. 6.16b,c). The parotid duct is very carefully dissected from the superficial fascia of the masseter muscle, and retracted by suture or muscle hook to avoid excessive trauma to the duct (Fig. 6.16d–f). The duct is dissected free posterior to the angle of the mandible or where the duct begins to divide into smaller ductules immediately rostral to the base of the parotid gland to provide adequate length for the duct’s relocation to the lateral conjunctival fornix (Fig. 6.16g). Separation of the parotid duct from the masseter muscle is continued rostrally; one must avoid the facial vein and the anastomotic nerve branch between the dorsal and ventral buccal nerves. Near the buccal mucosa, the parotid duct usually continues for about 0.5–1 cm submucosally before terminating in the papilla adjacent to the carnassial tooth.

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The lip is raised and the gauze sponge removed. The mucosa should not be penetrated beyond the submucosa. The papilla and surrounding 3 mm radius of mucosa are dissected free, and the papilla and parotid duct are retracted back into the initial external incision. The oral incision is apposed with 2-0 to 4-0 simple interrupted absorbable sutures. All instruments used within the mouth are set aside, and the surgeon should reglove. With a small straight hemostat or mosquito forceps, a subcutaneous tunnel is constructed to the lateral conjunctival fornix, superficial to the masseter muscle and the zygomatic arch. Pressure is applied until the instrument’s tips appear subconjunctivally and the overlying conjunctiva is incised. An alternative method is to excise a 2–3 mm diameter conjunctival plug. The mosquito forceps, placed within the subcutaneous tunnel, is used to grasp the edge of the mucosa with the papilla and carefully draw the duct to the conjunctival fornix (Fig. 6.16h). The mucosa about the papilla is trimmed, if excessive, and is sutured to the adjacent conjunctiva with at least three to four 6-0 simple interrupted absorbable sutures (Fig. 6.16i). The facial skin exposure is closed. Interrupted 2-0 to 4-0 absorbable sutures are used to reduce the ‘dead space’ between the subcutaneous tissues and the masseter muscle. The skin is apposed with simple interrupted 3-0 or 4-0 nonabsorbable sutures (Fig. 6.16j,k).

Oral approach for parotid duct transposition in dogs The oral approach for parotid duct transposition is an alterative method and was developed in humans to omit the postoperative skin incision and scarring. In this procedure, the initial step is to remove the oval mucosal plug with the papilla and then, by blunt–sharp dissection, free the duct from its masseter fascial attachments. A tunnel from the conjunctival fornix is formed from the ventrolateral conjunctival fornix with a mosquito forceps, and the mucosa and papilla are transposed to the conjunctival sac. The papilla of the parotid duct is apposed as in the previous method, and the oral incision is closed with 3-0 to 4-0 simple interrupted absorbable sutures.

Postoperative management and results Postoperative care after parotid duct transposition includes topical antibiotics and corticosteroids four to six times daily and systemic antibiotics for 7–10 days. If considerable facial edema occurs postoperatively, diuretics are useful. Gentle massage and occasional warm compresses to the surgical site help reduce the subcutaneous swelling and enhance duct function between meals. The skin sutures are removed in 7–10 days. Parotid duct function should be exhibited on the first postoperative day, with epiphora during snacks or meals. A drop of 1% atropine ophthalmic solution applied to the tongue can be used to check for duct patency, as well as to flush the debris associated with the trauma of surgery and cannulation from the duct or its papilla (or both). Parotid secretions may occasionally be intermittent, perhaps associated with subcutaneous facial edema, minor damage, or irregularities along the path of the duct. When the skin

Surgical anatomy

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Fig. 6.16 For parotid duct transposition in the dog, the parotid duct is cannulated with blue or green 2-0 to 4-0 monofilament nylon inserted into the papilla. (a) The mucosa around the papilla of the parotid duct (immediately adjacent to the carnassial tooth) is incised with a 4 mm skin trephine, and cannulated with a 2-0 monofilament nylon suture to facilitate its identification during the lateral surgical approach. (b) The skin incision is made directly over the cannulated duct, which can often be palpated. (c) The dotted line is the site for the skin incision directly along the parotid duct. (d) After the skin is incised, the parotid duct is carefully dissected from its deeper masseter muscle attachments, and differentiated from the dorsal and ventral buccal nerves. (e) Intraoperative photograph with the cannulated parotid duct (with blue nylon suture) exposed. A branch between the dorsal and ventral buccal nerves is external to the parotid duct and in the center of the surgical field. (f) The parotid duct is carefully separated from the fascial attachments to the masseter muscle from the base of the parotid gland to its distal opening into the mouth. (g) Intraoperative photograph showing the parotid duct papilla retracted into the lateral incision. The duct is routed subcutaneously to the lateral or ventrolateral conjunctival fornix (using a straight hemostat forceps). (h) The dissection is continued rostrally to the parotid duct papilla which may be incised from the surgical site, thereby freeing the entire parotid duct. A small hemostat is directed from the lateral ventral conjunctival fornix into the surgical site to protract the parotid papilla and duct for apposition to the conjunctival mucosa. (i) A lateral canthotomy can assist in the exposure of the lower conjunctival fornix. At least three 6-0 simple interrupted absorbable sutures are used to appose the parotid papilla mucosa to the conjunctival fornix. (j) Closure after parotid duct transposition consists of reduction of the dead space between the masseter muscle and the subcutaneous tissues with simple interrupted absorbable sutures, and apposition of the skin with simple interrupted non-absorbable sutures. The lateral canthotomy is apposed with simple interrupted non-absorbable sutures. (k) Immediate postoperative appearance after apposition of the parotid duct papilla to the conjunctival mucosa with three to five 5-0 to 6-0 simple interrupted absorbable sutures.

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sutures are removed, parotid duct function, as evaluated by the appearance of the eye and increased values of the Schirmer tear test, should be stabilized. Epiphora is usually evident only during eating. If the moisture to the eye is inadequate between meals, oral pilocarpine therapy is again initiated. After chronic KCS and successful parotid duct transposition, benefit to the eye becomes rapidly apparent. Corneal vascularization and pigmentation gradually decrease. Conjunctival exudates gradually decrease; their character changes from mucopurulent to seromucoid (Fig. 6.17). The surgical success rate of parotid duct transposition in the dog is high. Most investigators report 85–95% success rates with case follow-ups for as long as 5 years. Following surgery, patients with parotid duct transposition should be re-examined every 6 months.

Postoperative complications Most of the immediate postoperative surgical complications are related to the parotid duct’s small size. Transection and twisting of the parotid duct are obvious operative failures. Torsion of the duct greater than 180 may be manifested by intermittent, reduced, or absent secretions. Infections of the surgical wound after parotid duct transposition are rare, due to pre- and postoperative treatment with topical and systemic antibiotics. Absence of parotid secretions after a successful uncomplicated surgical technique and preoperative confirmation of parotid gland function for 3 or more days following surgery merits immediate surgical investigation. Postoperative focal stenosis of the parotid duct can occur in 1–8 weeks, associated with fibrosis. Parotid secretion is reduced or absent. To facilitate determination of the site of

Fig. 6.17 Miniature Schnauzer dog with bilateral parotid transposition of 3 years’ duration. Signs of the bilateral keratoconjunctivitis sicca have disappeared, and the dog is visual.

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obstruction, the surgeon may dilate the parotid duct proximal to the area of obstruction. Correction by careful removal of the fibrotic tissues surrounding the duct can be successful. Lack of parotid gland function can usually be detected preoperatively; loss of function postoperatively can be correlated to duct obstruction with subsequent pressure atrophy of the gland. The parotid gland may also undergo atrophy, perhaps associated with a generalized condition affecting all glandular tissues. About 10–20% of dogs with KCS also have xerostomia and are not candidates for parotid duct transplantation. Excessive saliva may be a problem in some dogs, but fortunately this is infrequent. In a few patients, ligation of smail branches of the parotid duct may eventually be necessary. In humans, partial resection of the parotid salivary gland has been performed to remedy this problem; however, it has not been reported in the dog, but seems possible. Expansion of the tear drainage apparatus is another possibility. Inadequate length of the parotid duct is not usually a problem in dogs, in contrast to humans. Elongation of the parotid duct by 1–2 cm can be achieved by construction of a tunnel of mucosa about the parotid duct papilla. Alternatively, dissection about the base of the parotid gland and rostral displacement can provide a marginal length parotid duct with several extra millimeters. White crystal-like precipitates occur infrequently postoperatively, but may occur more often than when parotid duct procedures were first performed in dogs. At the present time, the development of these crystals in dogs is the most frequent and often serious postoperative complication. Scrapings of these precipitates, as viewed by light microscopy, dissolve quickly in 0.5–1.0% EDTA solutions. These precipitates appear to be calcium carbonate, phosphate, oxalate, or a combination thereof. The precipitates occur on the corneal surface, conjunctivae, and nictitating membrane, and even adhere to the eyelid skin and hair, giving a ‘frosted appearance’ (Fig. 6.18).

Fig. 6.18 Occasionally after parotid duct transposition in the dog, precipitates of calcium oxalates, phosphates, and carbonates may form on the corneal and conjunctival surfaces, and even on the eyelid hair, giving a frosted appearance. These precipitates dissolve in 1% or 2% EDTA ointment, but once incorporated into the cornea or beneath the corneal epithelium do not usually respond to EDTA therapy. These precipitates seem associated with high rates of parotid secretion, and medical and/or surgical attempts to reduce the salivation rates may be beneficial.

Adaptations in large animals and special species

It appears that these precipitates are related to a high rate of parotid gland secretion: the higher the rate of parotid saliva formation, the higher the concentrations of these substances, and the greater the likelihood of their formation. If the cornea is ulcerated or has not epithelialized following a superficial keratectomy, deposition of this white material may be extensive. Use of 0.5% EDTA as a solution with a rinse cap, or preferably a 0.5–1.0% ointment, provides partial but not total removal of the precipitates. Frequent use of commercial eye washes with EDTA may also assist. Placement of the dog on a diet low in minerals for 1–2 months before parotid duct surgery, and maintenance thereafter, has been another approach. Surgical approaches to reducing the volume of salivary secretions are also possible and include: 1) a loose ligature using a non-absorbable suture along the middle of the transposed parotid gland’s duct; or, preferably, 2) two or three ligatures of accessory or feeder ducts at the level of the parotid gland. Both methods have successfully reduced the levels of salivary secretion, improved comfort, and reduced the amount of ocular irritation, but still maintained adequate Schirmer tear test levels. In addition, both methods can be repeated to lower further salivary secretion levels, if necessary.

Adaptations in large animals and special species The secretory abilities of the parotid gland vary by species. In ruminant species, parotid gland secretions are of very large quantities (as much as 50 L daily), and are critical to their rumination cycle and gastrointestinal function. Fortunately in the horse, the parotid salivary gland appears more limited in function and volume, rendering it useful for

surgical therapy of medically non-responsive keratoconjunctivitis sicca in horses. The horse parotid gland is still larger than its counterpart in ruminants, but apparently actively secretes only during chewing (the ruminant parotid gland continuously secretes).

Parotid duct transposition in the horse The parotid gland is located at the base of the ear, caudal to the mandible. The parotid duct arises from the combination of several collecting ductules at the base of the gland, and courses rostrad parallel to the facial vein. It continues anteriorly ventromedial to the mandible, and turns dorsally to pass the lateral mandible across the mandibular notch. Within this notch, the combination of the parotid duct, facial artery and vein can be palpated. From this notch, the parotid duct continues between the facial vein and masseter muscle to enter the oral cavity via a small papilla lying opposite the third cheek tooth. The surgical technique is modified from the dog and cat, by starting with a skin incision extending ventrally from the mandibular notch along the ventral aspect of the mandible to the base of the parotid duct. The parotid duct is identified and isolated from the base of the gland to within 4 cm of its oral papilla. Once adequate length is obtained, the duct is transected 4 cm from its papilla, and inserted through a subcutaneous tunnel to enter the lower conjunctival sac. The lumen of the distal duct is incised by scissors for about 3–4 mm, and the ends of the duct attached to the conjunctival mucosa with three simple interrupted absorbable sutures. Postoperative therapy is the same as for small animals. In one study, epiphora occurred during eating, but the previous eye irritation and signs of keratoconjunctivitis disappeared.

Further reading Small animals Baker GJ, Formston C: An evaluation of transplantation of the parotid duct in the treatment of keratoconjunctivitis sicca in the dog, J Small Anim Pract 9:261–268, 1968. Barnett KC: Imperforate and micro-lachrymal puncta in the dog, J Small Anim Pract 20:481–490, 1979. Betts DM: The surgical correction of parotid duct transposition failures, J Am Anim Hosp Assoc 13:695–700, 1977. Covitz D, Hunziker J, Koch SA: Conjunctivorhinostomy: a surgical method for the control of epiphora in the dog and cat, J Am Vet Med Assoc 171:251–255, 1977. Gelatt KN: Treatment of canine keratoconjunctivitis sicca by parotid duct transposition, J Am Anim Hosp Assoc 6:1–12, 1970. Gelatt KN, Guffy MM, Boggess TS: Radiographic contrast techniques for detecting orbital and nasolacrimal tumors in dogs, J Am Vet Med Assoc 156:741–746, 1970.

Gelatt KN, Cure TH, Guffy MM, Jessen CL: Dacryocystorhinography in the dog and cat, J Small Anim Pract 13:381–397, 1972. Giuliano EA, Moore CP: Diseases and surgery of the lacrimal secretory system. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 633–661. Giuliano EA, Pope ER, Champagne ES, et al: Dacryocystomaxillorhinostomy for chronic dacryocystitis in a dog, Vet Ophthalmol 9:89–94, 2006. Glen JB, Lawson DD: A modified technique of parotid duct transposition for the treatment of keratoconjunctivitis sicca in a dog, Vet Res 88:210–213, 1971. Grahn BH, Sandmeyer LS: Diseases and surgery of the canine nasolacrimal system. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 618–632. Guinan J, Willis AM, Cullen CL, Walshaw R: Post-enucleation orbital sialocele in a dog associated with prior parotid duct transposition, Vet Ophthalmol 10:386–389, 2007.

Gwin RM, Gelatt KN, Peiffer RL: Parotid duct transposition in the cat with keratoconjunctivitis sicca, J Am Anim Hosp Assoc 13:42–45, 1977. Hallstrom M: Transplantation av ductus parotideus som behandlingsmethod vid kerato-conjunctivitis sicca hos hund, Nord Vet Med 23:5–8, 1971. Harvey CE, Koch SA: Surgical complications of parotid duct transposition, J Am Anim Hosp Assoc 7:122–126, 1971. Kamiya S, Horiuchi T, Hatakeyama A, Abe K, Matumura T: Transplantation of the parotid duct into the conjunctival sac for the treatment of xerophthalmia, Jpn J Ophthalmol 3:189–196, 1959. Kaswan RL, Salisbury MA: A new perspective on canine keratoconjunctivitis sicca: treatment with ophthalmic cyclosporine, Vet Clin North Am: Small Anim Pract 20:583–613, 1990. Laing EJ, Spiess B, Binnington AG: Dacryocystotomy: a treatment for chronic dacryocystitis in the dog, J Am Anim Hosp Assoc 24:223–226, 1988.

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Lavignette AN: Keratoconjunctivitis sicca in a dog treated by transposition of the parotid salivary duct, J Am Vet Med Assoc 148:778–786, 1966. Long RD: The relief of epiphora by conjunctivorhinostomy, J Small Anim Pract 16:381–386, 1975. Moore CP: Dry eye syndromes: KCS and other tear deficient diseases, Transactions of the North American Veterinary Conference 14:560–562, 2000. Murphy JM, Severin GA, Lavach JD: Nasolacrimal catheterization for treating chronic dacryocystitis, Vet Med 72:883–887, 1977. Pope ER, Champagne ES, Fox D: Intraosseous approach to the nasolacrimal duct for removal of a foreign body in a dog, J Am Vet Med Assoc 218:541–542, 2001. Salisbury MA, Kaswan RL, Ward DA, et al: Topical application of cyclosporine in the management of keratoconjunctivitis sicca in dogs, J Am Anim Hosp Assoc 26:269–274, 1990. Schilke HK, Sapienza JS: 2008, Partial ligation of the transposed parotid duct at the level of the parotid gland for excessive salivary secretions in the Yorkshire terrier breed. In Proceedings of the 39th Meeting of the

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American College of Veterinary Ophthalmologists: Abstract 11. Schmidt G, Magrane WG, Helper LC: Parotid duct transposition: a follow-up study of 60 eyes, J Am Anim Hosp Assoc 6:235–241, 1970. Severin GA: Nasolacrimal duct catheterization in the dog, J Am Anim Hosp Assoc 8:13–16, 1972. Smythe RH: Veterinary Ophthalmology, ed 2, London, 1958, Baillie`re, Tindall and Cox, pp 206–207. Stanley RG: Failure of parotid duct transposition due to sialolith formation, Veterinary and Comparative Ophthalmology 7:26–127, 1997. Startup FG: Intra-canalicular gelatin implants in lacrimal punctum surgery, J Small Anim Pract 25:635–637, 1984. White RAS, Herrtage ME, Watkins SB: Endoscopic management of a cystic naso-lacrimal obstruction in a dog, J Small Anim Pract 25:729–735, 1984.

Large animals and special species Brooks DE, Matthews AG: Equine ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 1165–1274.

Burling K, Murphy CJ, da Silva Curiel J, Koblik P, Bellhorn RW: Anatomy of the rabbit nasolacrimal duct and its clinical implications, Progress in Veterinary and Comparative Ophthalmology 1:33–40, 1991. Maitchouk DY, Beuerman RW, Ohta T, Stern M, Varnell RJ: Tear production after unilateral removal of the main lacrimal gland in squirrel monkeys, Arch Ophthalmol 118:246–252, 2000. Mangan BG, Gionfriddo JR, Powell CC: Bilateral nasolacrimal duct atresia in a cria, Vet Ophthalmol 11:49–54, 2008. McIlnay TR, Miller SM, Dugan SJ: Use of canaliculorhinostomy for repair of nasolacrimal duct obstruction in a horse, J Am Vet Med Assoc 218:1323–1324, 2001. Millichamp NJ, Jacobson ER, Dziezyc J: Conjunctivoralostomy for treatment of an occluded lacrimal duct in a blood python, J Am Vet Med Assoc 189:1136–1138, 1986. Townsend WM: Food and fiber-producing animal ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 1275–1335. Wilkie DA, Rings DM: Repair of anomalous nasolacrimal duct in a bull by use of conjunctivorhinostomy, J Am Vet Med Assoc 196:1647–1650, 1990.

CHAPTER

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Surgical procedures for the conjunctiva and the nictitating membrane Kirk N. Gelatt1 and Dennis E. Brooks2 1

Small animals; 2Large animals and special species

Chapter contents Introduction

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Adaptations in large animals and special species

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Conjunctival anatomy

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SURGERIES OF THE NICTITANS

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Anatomy of the nictitans

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Surgical treatment of everted nictitans

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Bulbar/palpebral conjunctival biopsy (punch/snip)

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Surgical treatment for hyperplastic lymphoid follicles

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Surgical repair of conjunctival lacerations

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Surgical repair of conjunctival defects

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Surgical procedures for protrusion of the gland of the nictitating membrane or ’cherry eye’

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Adaptations in large animals and special species

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Surgical procedures for prominent/protruded nictitans

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Surgical treatment for symblepharon

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Nictitating membrane flaps

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Conjunctival grafts/transplantation

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Partial/complete excision of the nictitans

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Substitute materials for conjunctival grafts

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Adaptations in large animals and special species

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Introduction Conjunctival and nictitating membrane diseases occur frequently in all animals. In the dog, the majority of conjunctival inflammations are secondary, and bacteria isolated from these eyes usually yield a variety of normal residents of the conjunctival surfaces. In the cat, most conjunctival inflammations are primary, infectious, and associated with viruses, chlamydia, and mycoplasma. In horses, primary conjunctivitis is infrequent, but both the conjunctiva and the nictitans are often involved with neoplasia in older horses. In cattle, primary inflammations and neoplasia of the conjunctiva and nictitans are frequent. Surgery for conjunctival diseases in the dog and cat is infrequent except for excision of conjunctival masses, which are often combined with other surgical procedures involving the eyelids. The most frequent conjunctival surgical procedures are the several different types of conjunctival grafts or flaps for treatment of corneal ulcers that threaten the integrity of the globe, and the maintenance of vision. Fortunately, there is ample and mobile conjunctiva for the

construction of these grafts. The success rates for the different conjunctival autografts are very high (>90%), and their value in the overall clinical management of small animal patients is often understated. In horses and cattle, neoplasia is often treated with surgery, sometimes combined with cryotherapy or local chemotherapy. The nictitating membrane has several synonyms including membrana nictitans, palpebra tertia, plica semilunaris, third eyelid, and the haws. The nictitating membrane is a semilunar fold of conjunctiva, which also occurs in redimentary form in humans and non-human primates, that protrudes from the medial canthus and can extend over a significant portion of the cornea. It is more mobile in birds and cats, and in birds it is very thin and semitransparent. Diseases of the nictitating membrane are not infrequent in small animals. In dogs and cats, congenital, inflammatory, traumatic, and neoplastic disorders may be treated surgically. In cats, more frequently than in dogs, disorders of the nictitating membranes may also signal serious systemic diseases. In both horses and cattle, neoplasms are the most frequent surgical indications.

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Surgical procedures for the conjunctiva and the nictitating membrane

Movement of the nictitating membrane somewhat parallels its development in the different species. In dogs, the dorsolateral movement of the nictitating membrane appears passive and associated with movement of the retractor oculi muscle, and the shifting of the endorbita fascia and orbit fat pad. As the globe is retracted into the depths of the orbit, the orbital adipose tissues shift forward to push the base of the nictitating membrane anteriorly and protract the structure across the cornea. Fascial attachments in the canine nictitating membrane attach the base of the hyaline cartilage and the nictitans tear gland to the bulbar fascia, medial canthal ligament, and endorbita or periorbita fascia. In cats, movements of the nictitating membrane result from contraction of smooth muscles, and are associated with its sympathetic nerve supply. Stimulation of the preganglionic cervical sympathetic nerve produces frequencydependent contractions of the nictitating membrane. The feline nictitating membrane contains two thin sheets of muscle, named by Acheson in 1938 as the medial and inferior muscles (also called Mu¨ller’s muscles), that arise deeply within the orbit from the periorbital fascia covering the medial and ventral rectus muscles to insert into the adjacent sides of the T-shaped nictitans cartilage. Alpha1-adrenoceptor antagonists, whether selective or non-selective, produce a dose-dependent depression of the evoked nictitating membrane movements, suggesting that the feline nictitans contains mainly a1-adrenoceptors postsynaptically. In horses and cattle, movements of the nictitans result from contraction of the rectus and retractor oculi muscles which displace the orbital fat rostrally and protract the nictitans across the cornea in a more horizontal direction. In birds, the active movement of the nictitating membrane is highly developed, and is rapidly protracted over the cornea toward the lateral canthus by the pyramidalis muscle. Protraction of the third eyelid is accomplished by contraction of the striated pyramidalis muscle that originates in the posterior sclera and attaches to the nasal edge of the nictitans. The quadratus muscle forms a sleeve dorsal to the optic nerve through which the tendon of the pyramidalis muscle passes, allowing a pulley action of the quadratus muscle to amplify or modify action of the pyramidalis. Innervation of both muscles by the sixth cranial nerve is widely cited. The leading edge is pigmented and forms a marginal plait (plica marginalis). The avian nictitans can be very thin and difficult to appose by sutures after trauma.

tarsus, septum orbitale, and the endorbita. The collective conjunctiva is often referred to as the conjunctival sac. Traditionally the conjunctiva is divided macroscopically into palpebral, fornix, and bulbar components. The palpebral conjunctiva lines the inner aspects of the eyelids. The bulbar conjunctiva mucosa starts at the corneal epithelial layer at the limbus. It covers Tenon’s capsule or bulbar fascia, and extends to join the palpebral conjunctiva at the fornix or the conjunctival cul-de-sac. Tenon’s capsule or bulbar fascia is quite thin in cats, horses, and cattle but variable in dogs, sometimes 5 mm or more thick. Medially a conjunctival apex or fold, the nictitating membrane or third eyelid, divides the ventral conjunctival fornix into two parts: the outer or palpebral portion, and the deeper or bulbar component (Fig. 7.1). As the conjunctival fornices span the globe and eyelids for 360
, the fornices may be divided into dorsal, lateral canthal, ventral, and medial canthal parts. The dorsal conjunctival fornix is deeper than the ventral fornix, and this may be necessary to accommodate downward eye movements. The ventral conjunctival fornix is shallower and its primary function is as a collecting basin for the tears. The medial conjunctival fornix is divided into anterior and posterior fornices of the nictitating membrane. Medial movement of tears toward the upper and, more

C B

A

Conjunctival anatomy Conjunctival anatomy is similar in all mammals. The conjunctiva spans the eyelid margins to the limbus of the globe and is the major barrier to the external environment for the globe and orbit. The conjunctiva, as a mucous membrane, forms the first line of defense against the external elements. Its elastic nature accommodates both globe and eyelid movements. The conjunctiva rests on the endorbita or periorbita fascia; on the globe the conjunctiva is in intimate contact with the bulbar fascia (or Tenon’s capsule) and attaches at the limbus. As a result, the conjunctiva accommodates globe mobility and provides for nearly unrestricted ocular movements. The conjunctiva lining the inner aspects of the eyelids and fornix for 360
is next to the fibrous

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D E F

Fig. 7.1 Cross-section of the medial eyelids and anterior globe to demonstrate the palpebral conjunctiva (A), bulbar conjunctiva (B), and dorsal fornix (C) of the conjunctiva. The nictitating membrane (D) divides the medial lower conjunctival fornix into anterior or palpebral (E), and posterior or bulbar portions (F).

Anatomy of the nictitans

importantly, the lower lacrimal puncta by the eyelid is not understood, but it appears to be an active rather than a passive process. The palpebral conjunctiva originates at the eyelid margin (the margo-intermarginalis) and the orifices of the meibomian glands. The margo-intermarginalis is the last tissue that when contact occurs with the cornea and conjunctiva produces no damage; when the outer leading edge of the eyelid skin touches the cornea, as in entropion, corneal and conjunctival damage start! The palpebral conjunctival surface epithelium at the eyelid margin consists of nonkeratinized stratified epithelium, but changes after several millimeters from the lid margin into pseudostratified columnar epithelium. Immediately beneath the palpebral conjunctiva is the thicker connective tissue, the tarsal layer, which contains the sebum-producing tarsal or meibomian glands. Once the pseudostratified epithelial surface is established, conjunctival goblet cells begin to appear and are most numerous in the fornices. These goblet cells produce mucin, an important deep component of the preocular or precorneal film, and an essential lubricant to prevent eyelid trauma to the conjunctival and the corneal surfaces (Fig. 7.2). Mucin forms the innermost layer of the preocular (precorneal) film and ranges in thickness from 1 mm on the cornea to 2 mm or more on the conjunctival surfaces. Mucin, a hydrated glycoprotein, forms an interface between the larger aqueous portion of the preocular film and the hydrophobic corneal epithelium. A relatively small portion of mucin is water soluble and part of the middle or aqueous fraction of the preocular film. The goblet cell-derived mucin decreases the surface tension of the preocular film, enhances the stability of the preocular film, and aids in the coherence of the aqueous portion of the preocular film to the corneal and conjunctival epithelia. Mucin also coats and reduces the irregularities of the corneal epithelium to produce an optically smooth corneal surface. The palpebral conjunctiva is quite transparent and often allows visualization of impacted or inflamed meibomian (or Meibom) glands on the deep aspects of both eyelids. The bulbar conjunctiva consists of entirely pseudostratified epithelium, and is most firmly attached at the fornices and the limbus. About 3 mm from the corneal periphery,

the bulbar conjunctiva, Tenon’s capsule (orbital fascia), and the limbus become closely united. Because of its surface area and availability, the dorsal bulbar conjunctiva is the principal source of mucous membrane for graft construction and transplantation to the cornea. The bulbar conjunctiva contains few goblet cells. The limbal conjunctival cell may have special significance as a critical stem cell for conjunctival surgical procedures. Transplantation of limbal stem autografts to defects in the corneal epithelium in humans successfully re-establishes the corneal epithelial characteristics and clarity, and offers potential for animals. Normal corneal epithelial cells migrate centripetally from the periphery to the center of the cornea. The limbal cells appear to be the corneal epithelial stem cells and capable of additional cell multiplication and differentiation, and a terminal transparent cell. Epithelial cells from the limbus readily grow as explants; however, peripheral and central corneal explants are progressively less likely to grow as explants. The peripheral and, to a greater extent, the central corneal epithelial cells appear committed to terminal differentiation. As a result, both the limbal and conjunctival epithelia are excellent sources for autografts. Lymphoid follicles are scattered throughout the conjunctiva, but may be more numerous in the fornices. These lymphoid follicles, acting as regional lymph nodes, are the major defense for the conjunctival surfaces, and during inflammation increase both in size and number. Grossly lymphoid follicles appear as clear-to-translucent raised circular areas. The substantia propria of the conjunctiva consists of two layers: a superficial layer that contains lymphatic follicles and glands, and the deeper fibrous layer that attaches the conjunctiva to the orbital and eyelid fascia. The latter layer tends to be quite variable in dogs, and in certain breeds is sometimes quite thick; however, in contrast, it tends to be quite thin in cats, horses, and cows. In the preparation of bulbar conjunctival grafts, the thickness of this layer can contribute to excessive tension of the graft and retraction toward the limbus. The nerves and vessels of the conjunctiva are primarily in the deep layer, and are derived from the anterior ciliary arteries that are branches from the external ophthalmic arteries. Additional arterial branches arise from the superficial temporal, malar, and palpebral arteries. Venous drainage from the conjunctiva occurs to adjacent palpebral and malar veins that eventually join the facial vein, or deep into the orbit with the superficial angularis oculi vein to the orbital plexus and superficial temporal vein. The lymphatics of the conjunctiva are divided into superficial and deep systems. Lymphatic drainage from the medial aspects of the conjunctiva is to the submaxillary lymph nodes and laterally to the parotid lymph nodes.

Anatomy of the nictitans

Fig. 7.2 Photomicrograph of the canine palpebral conjunctiva near the fornix. The goblet cells (stained red), the primary source of mucin for the preocular film, are outlined by periodic acid–Schiff stain. 200.

The gross anatomy of the nictitating membrane is quite similar among mammals. Located in the medial canthus, the nictitating membrane is a roughly triangular-shaped fold of conjunctiva, with the base of the triangle consisting of its free or leading margin (Fig. 7.3). Both anterior (palpebral) and posterior (bulbar) surfaces are confluent with the

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Fig. 7.3 By distortion of the palpebral fissure, the canine globe retracts to partially protrude the nictitating membrane. Note its pigmented margin.

palpebral and bulbar conjunctival mucosa. Its free margin or border is usually pigmented in animals. When nonpigmented, the nictitans appears more prominent. Within the substance of the nictitating membrane is a hyaline T-shaped cartilage plate, which helps provide rigidity to the structure, assists conformation to the corneal curvature, and prevents disfigurement during movement (Fig. 7.4). The ’arms’ of the T-shaped cartilage are immediately under its leading margin, and are relatively thin and slender compared to the thicker stem or base. The superficial gland of the nictitating membrane in both dogs and cats surrounds the base of the nictitans cartilage and produces seromucoid tears. Both dogs and cats possess a single nictitans gland, but in some species such as birds, the third eyelid gland may have two divisions. The deeper avian third eyelid gland is referred to as the Harderian gland. In horses, the nictitans gland is quite large (19 mm anteroposterior  11 mm wide). In cattle, the triangular-shaped nictitans gland (41 mm long  26 mm wide) is in two parts, although it appears as one confluent structure: the anterior seromucoid nictitans gland which surrounds the cartilage shaft (serous-appearing acini, but periodic acid–Schiff positive), and the deeper Harderian gland, which also has two parts, and is also mucoid but periodic acid–Schiff negative.

C

The nictitans gland in small animals is an important accessory tear-producing gland providing about 25–40% of the total tears. Lymphoid follicles are usually present on the posterior or bulbar surface of the nictitans, appearing as raised translucent spots, and especially prominent in the horse. Lymphoid follicles are infrequent on the anterior or palpebral surface of the nictitating membrane and often signal chronic conjunctival irritation. The blood supply to the canine nictitating membrane is derived from a branch of the internal maxillary artery located within the space between the ventral and medial rectus muscles. Smaller branches are often located on both sides of the stem portion of the cartilage and should be avoided during surgery. Sensation is provided by the infratrochlear nerve branch of the ophthalmic nerve, a subdivision of the trigeminal nerve. The primary functions of the nictitating membrane are to assist in the protection of the cornea and provide the second largest portion of tears. Mucin from the third eyelid tears forms an essential part of the preocular film. Nictitating membrane movement may assist in the movement of tears to the medial canthus, and the ’pick-up’ of the tears by the lacrimal puncta. Loss of the nictitans results in a larger medial lacrimal lake or conjunctival sac and often chronic conjunctivitis due to the collection and impaired drainage of tears from this area. The nictitating membrane is an essential component of the conjunctiva as well as the tearproducing system. Total excision of the nictitating membrane should be reserved for extensive neoplastic involvement of this structure.

Bulbar/palpebral conjunctival biopsy (punch/snip) Biopsy of the conjunctiva may be indicated for diagnosis of non-specific diffuse and focal conjunctival inflammations (Fig. 7.5), and for possible neoplasia in all animal species. For biopsies of suspected conjunctival inflammations,

A

B

D

Fig. 7.4 The important surgical anatomy of the nictitating membrane includes the leading margin (A), its base (B), the T-shaped hyaline cartilage (C), and the superficial gland of the nictitans (D).

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Fig. 7.5 Aged mixed-breed dog with episcleritis. Located beneath the dorsal bulbar conjunctiva, the inflammatory mass is raised and bright red. A wide excisional biopsy was performed.

Surgical repair of conjunctival lacerations

selection of the ventral conjunctiva may be more rewarding. Focal swellings, such as conjunctival cysts, parasitic granulomas, nodular granulomatous episclerokeratitis, proliferative keratoconjunctivitis of Collies, and nodular fasciitis, can be biopsied or removed for histologic examination. In contrast to the majority of eyelid neoplasms in the dog, primary conjunctival neoplasms may be invasive locally and should be widely excised. Hemangiomas, hemangiosarcomas, angiokeratomas, viral papillomas, squamous cell carcinomas, and malignant melanomas have been reported in the dog. In the cat, the most frequent conjunctival neoplasm is squamous cell carcinoma. Neoplasms of the conjunctiva affect the dorsal to dorsolateral limbal area most frequently, suggesting solar (ultraviolet) radiation may play an important role in their genesis. If a conjunctival neoplasm penetrates the anterior orbital fascia, intraorbital extension is likely and the clinical appearance of the neoplasm may be deceptive. In the clinical assessment before excision, involvement of the deeper layers of the conjunctiva should be determined by ultrasonography or other imaging procedures. If the mass involves the superficial layers of the conjunctiva, it is usually easily manipulated and moves with the conjunctival mucosa. If the tumor has extended into the deeper submucosa or even infiltrated the periorbital fascia, the tumor usually remains fixed as the surrounding conjunctiva is manipulated. In horses and cattle, solitary masses of the conjunctiva are assumed to be neoplastic until proven different histologically. In both species, squamous cell carcinomas are the most frequent neoplasms, affecting the eyelid margin, nictitans, and limbus. Because of malignancy and infiltration of adjacent tissues, surgery is often combined with other treatment modalities, such as cryotherapy. Sedation or short-acting general anesthesia is usually necessary for conjunctival biopsy. Topical anesthesia, such as 0.5% proparacaine or 0.5% tetracaine, can also be used. The eyelids are not usually clipped or prepared for surgery. The conjunctival surfaces, including the fornices, are cleansed with sterile cotton-tipped applicators and 0.5% povidone– iodine solution. The elastic and accessible conjunctiva can be easily biopsied. Small biopsies less than 1 cm do not require sutures and readily heal by secondary intention. The eyelids are retracted with a small wire speculum, conjunctival area to be biopsied is elevated by small thumb forceps, such as the Bishop–Harmon, and the conjunctiva excised by small tenotomy scissors. If the conjunctival defect is greater than 1 cm, the mucosa edges are apposed with 4-0 to 7-0 simple interrupted or continuous absorbable sutures. Postoperative treatment usually consists of topical antibiotics or antibiotics/corticosteroids administered three or four times daily for several days.

Surgical repair of conjunctival lacerations Conjunctival lacerations are infrequent and usually combined with lacerations of the eyelids, cornea, and sclera. The presence of bulbar conjunctival lacerations signals the need for a complete eye examination. Bulbar conjunctival lacerations may mask more serious and vision-threatening full-thickness scleral lacerations and intraocular damage.

Small conjunctival lacerations less than 1 cm will usually heal by secondary intention. These lacerations should be carefully examined to exclude any intraocular damage, and any foreign material removed manually or irrigated from the tissues. Topical antibiotic solutions are administered several times daily for 5–7 days, or until the conjunctival epithelium has bridged the wound. Larger conjunctival lacerations are usually apposed by sutures. Palpebral conjunctival wounds often involve the full-thickness eyelids. Large bulbar conjunctival lacerations should be approached with caution, as intraocular tissue involvement is likely. If hyphema is present with a bulbar conjunctival laceration, intraocular damage has occurred, and careful examination of the entire globe is warranted. Both direct and indirect trauma can result in intraocular hemorrhage and inflammation. Large conjunctival lacerations (>1 cm) are best treated by apposition with sutures. After short-acting general anesthesia, the conjunctival surfaces are carefully cleaned with cotton-tipped applicators and, if necessary, with serrated thumb forceps. Any foreign material should be removed and, if possible, identified. Vegetative material will often provoke an acute and intense inflammation. Fungal organisms may also be introduced into the tissues. Debridement of conjunctival tissues, like that of the eyelids, should be minimal to preserve as much of the conjunctiva as possible. Small thumb forceps with 1  2 teeth and a small Castroviejo needle holder are used. Simple interrupted absorbable sutures (usually 5-0 to 7-0) are used for apposition. Some chemosis is anticipated postoperatively. Topical antibiotics, often combined with corticosteroids, are instilled four to six times daily for 5–7 days. The ointment form of medication may be more advantageous as drug contact time is prolonged, and the ointment coats the conjunctival and suture surfaces to act as a lubricant. If the conjunctival swelling is excessive, hot and cold packs to the area may promote local circulation and reduce the swelling. Systemic antibiotics and corticosteroids are also added to the topical therapy for more serious conjunctival lacerations. Topical and systemic (oral) non-steroidal anti-inflammatory agents can also be added. Conjunctival healing after lacerations is usually uneventful. Focal scar tissue formation is usually minor and not sufficient to restrict globe mobility or eyelid movements. Palpebral conjunctival lacerations usually signal full-thickness eyelid perforations. In most small animals, full-thickness eyelid lacerations are repaired by two layers of sutures: one layer for the eyelid skin and orbicularis oculi muscle, and the second and deeper layer for the tarsus and palpebral conjunctiva. Both layers may be apposed by 4-0 to 6-0 simple interrupted sutures, absorbable sutures for the deep layer and non-absorbable sutures for the muscle and skin layer. The deep layer of the tarsus and palpebral conjunctiva may also be apposed with a simple continuous suture. The suture apposing the eyelid margin is most important and is often a figure-of-eight stitch that either avoids the eyelid margin with its knot or is temporarily positioned in the opposite eyelid to provide some tension on the healing conjunctiva and eyelid tissues. Postoperative treatment varies with the depth and extent of the palpebral conjunctival and eyelid lacerations. Often topical antibiotics and corticosteroids are supplemented

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with systemic antibiotics and corticosteroids. The eyelids after trauma and laceration apposition may become quite swollen. The swelling may elicit self-trauma by the patient. Accordingly, an E-collar is often used to ensure the patient cannot damage the postoperative area. The skin sutures are removed in 7–14 days, sometimes at two different times.

Surgical repair of conjunctival defects Conjunctival defects may occur after the excision of large conjunctival dermoids (Fig. 7.6) and neoplasms, after loss from severe trauma, and extensive chemical burns. Fortunately, large conjunctival defects are infrequent in animals and may be repaired by a number of techniques. In contrast to the lid tumors in most species, conjunctival neoplasms tend to be more aggressive clinically and merit larger incisional margins during attempted excision. Small conjunctival defects (1 cm) should be apposed by sutures. For bulbar conjunctival defects of about 2 cm or larger, the adjacent conjunctiva may be undermined and shifted to cover the defect. For larger defects, autografts of bulbar conjunctiva from the opposite fellow eye or the buccal mucosa may be transplanted. The mucosa is usually harvested free-hand, must be thin, and 1–3 mm larger than the defect to compensate for tissue shrinkage. The edges of the transplant are carefully apposed to the wound with 4-0 to 7-0 simple interrupted absorbable sutures. Often an incomplete temporary tarsorrhaphy is performed after conjunctival transplantation to prevent eyelid trauma and apply pressure to the surgical site to retard swelling. Autografts of conjunctiva and buccal mucosa to the conjunctiva in small animals are highly successful. When the conjunctival wound or autograft edges involve the limbal area, the conjunctival margin is apposed to the limbus by sutures to avoid overgrowth or migration onto the cornea.

Carcinoma in situ of the conjunctiva can be excised with sedation, an auriculopalpebral nerve block, and topical anesthetic in a good horse.

Surgical treatment for symblepharon Symblepharon is the adhesion of bulbar to palpebral conjunctiva, the adhesion of the palpebral conjunctiva to the cornea, or the adhesion of the bulbar conjunctiva to the cornea. Symblepharon can also involve the nictitating membrane. Symblepharon is rare in dogs, but more frequent in cats. In horses, symblepharon may follow trauma, and either no surgical correction or improper surgical alignment. In dogs, symblepharon may develop after trauma, surgery, and chemical burns to the cornea and conjunctiva. In cats with ocular herpes (FHV-1), symblepharon may develop usually involving the cornea and the bulbar conjunctiva, the palpebral conjunctiva, or a combination of both conjunctivae (Fig. 7.7). Symblepharon associated with FHV-1 can be corrected successfully in cats, but since these corneal and conjunctival inflammations are often chronic, symblepharon formation may recur. Symblepharon affecting the cornea produces disfigurement and, if extensive, impairment of vision. Adhesions involving the bulbar and palpebral conjunctivae may shallow the conjunctival fornix, impair the drainage of tears, produce chronic conjunctivitis, and retard ocular motility. The objectives for the surgical correction of symblepharon are to excise the fibrous adhesions between the conjunctiva and cornea, and to restore viable epithelial surfaces to the palpebral and bulbar conjunctivae, and to the cornea. Various conformers, symblepharon lenses, and silicone strips are available to physically separate the healing conjunctival surfaces and help establish and maintain the conjunctival fornix. These temporary implants are generally retained in position by complete temporary tarsorrhaphies for a few weeks for the epithelial healing to be completed. If any of

Adaptations in large animals and special species Surgical resection alone of conjunctival squamous cell carcinoma may be adequate if clean margins can be obtained. Small tumors or carcinoma in situ of the conjunctiva or third eyelid may also be effectively treated with simple excision.

Fig. 7.6 Dermoid in a puppy affecting only the palpebral conjunctiva. Treatment is excision of the mass.

162

Fig. 7.7 Symblepharon in a 2-year-old, short-haired, domestic cat. The symblepharon involves the lateral cornea, bulbar and palpebral conjunctiva. The patient has recurrent conjunctivitis and keratitis associated with feline herpes virus (FHV-1).

Conjunctival grafts/transplantation

these corneal or conjunctival structures is not covered with epithelium postoperatively, adhesions will recur. After general anesthesia, clipping of the eyelid hair, and surgical preparation of the eyelids, the area is draped for aseptic surgery. The conjunctiva is thoroughly cleaned with sterile saline and all foreign material removed by cottontipped applicators. After placement of a wire speculum to retract the eyelids, the conjunctiva adhered to the cornea is removed by superficial lamellar keratectomy. The periphery of the corneal lesion is incised by the Beaver No. 6400 microsurgical blade to the level of the superficial stroma (Fig. 7.8a). After lifting the edge of the incision with thumb forceps with 1  2 fine teeth jaws, the adherent conjunctiva is excised from the corneal surface (Fig. 7.8b). If the symblepharon continues into the conjunctiva, the incision is continued and the affected conjunctiva excised (Fig. 7.8c). Once the conjunctiva is freely moveable, its edge is apposed to the limbus with 5-0 to 7-0 simple interrupted absorbable sutures. If a defect remains in the bulbar and/or palpebral conjunctiva, its edges are apposed with 5-0 to 7-0 simple interrupted absorbable sutures. To cover the healing cornea and prevent the development of new adhesions between the cornea and conjunctiva, a plastic methyl methacrylate corneal protector (Crouch corneal protector; Storz, St Louis, MO) may be inserted or amniotic membrane apposed by sutures. A soft corneal contact lens may be used instead of the thicker corneal protector (Fig. 7.8d). If considerable adhesions are present between the bulbar and palpebral conjunctivae, a thin strip of silicone sheeting is fashioned to fill the area and secured in position with 4-0 to 7-0 simple interrupted non-absorbable sutures as well as 5-0 to 7-0 simple mattress sutures placed through the silicone strip and the full-thickness eyelid with the suture knots on the external lid surface

(Fig. 7.8e). To retain the corneal contact lens and reduce eyelid movements, a partial temporary tarsorrhaphy is performed with 4-0 to 6-0 simple mattress sutures positioned at one-half thickness of the eyelids (Fig. 7.8f). For details on how to perform the temporary tarsorrhaphy, see Chapter 5. After recovery from general anesthesia, an E-collar is placed on the animal to prevent self-mutilation of the surgical site. Postoperatively, topical antibiotic solution is instilled on the eye four to six times daily. Systemic antibiotics are also administered. Once corneal epithelialization is complete, as evidenced by the lack of topical fluorescein, topical corticosteroids are added to reduce scar tissue formation. After 2–4 weeks, the tarsorrhaphy sutures are released to remove the corneal contact lens. About 2 weeks later, the fornix silicone strip and sutures are removed. Topical antibiotics/ corticosteroids are continued for another 7–10 days. This procedure provides good results in dogs and cats in which the symblepharon was secondary to trauma or chemical burns, provided the contact lens is retained in position for several weeks to permit complete epithelialization of the apposing conjunctival surfaces. This method is less successful in cats when the symblepharon appears secondary to chronic feline herpes virus infections, because with recurrent or chronic FHV-1 the corneal and conjunctival epithelia may be damaged again and re-adhesion occurs.

Conjunctival grafts/transplantation Conjunctival grafts or flaps were first performed in humans in 1860 (Teale) and 1884 (Bock) for the treatment of symblepharon. Conjunctival autografts for the treatment of corneal ulcerations in humans for the past several decades

A

B

C

D

E

F

Fig. 7.8 Surgical treatment of symblepharon in the cat. (a) The corneal portion of the symblepharon is excised by superficial keratectomy. The periphery of the corneal lesion is incised by Bard–Parker No. 15 or Beaver No. 6400 blade to the level of the superficial stroma. (b) With fine teeth thumb forceps, the edge of the corneal incision is elevated, and the adherent conjunctiva is dissected from the anterior corneal stroma. (c) Excision of the adherent conjunctiva is continued onto the affected bulbar and palpebral conjunctival surfaces. (d) After apposition of the remaining conjunctiva to the limbus with 5-0 to 7-0 simple interrupted absorbable sutures, a corneal protector is positioned on the cornea to cover the corneal stroma and attempt to prevent re-adherence of the conjunctiva. (e) A strip of silicone sheeting is inserted into the lower conjunctival fornix to maintain the separation between the ventral bulbar and palpebral conjunctiva, and secured with 5-0 to 7-0 simple mattress sutures placed full-thickness through the eyelids. (f) A partial temporary tarsorrhaphy is performed to protect the surgical sites, retain the corneal protector during the epithelialization of the corneal wound, and maintain the silicone sheeting in the fornix to separate the healing conjunctival surfaces.

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have been replaced by partial- and full-thickness keratoplasty. The major reason is the high visual acuity in humans and the absolute need for a clear cornea. Nevertheless, conjunctival autografts are still used in humans for fungal keratitis, selected herpes simplex ulcerations, and chemical burns of the cornea. Reports of bulbar and palpebral conjunctival grafts and conjunctival keratoplasty first appeared in the veterinary medical literature more than 50 years ago (Uberreiter 1937, Shuttleworth 1939, Stern 1950, Livingston 1950, Henderson 1951, Dimic 1957, and Berge and Westhues 1956). Most reports described advancement bulbar conjunctival grafts, complete bulbar conjunctival grafts, and palpebral conjunctival grafts. In veterinary ophthalmology the routine use of keratoplasty has not yet occurred, but the development of conjunctival autografts for the surgical management of corneal ulceration has been continuously refined. As a result, more transparent corneas now result. Further improvements may follow in the future using porcine small intestinal submucosa (available commercially) and amniotic membranes (not available commercially), rather than conjunctival grafts. Because the veterinary ophthalmologist is concerned first for the preservation of the globe and second for clinical vision in animals, the cornea need not be perfectly and totally clear. As each animal has ample bulbar and palpebral conjunctivae for temporary or even permanent transplantation to the cornea, availability and host acceptance are not limiting factors. Treatment of deep corneal ulcerations, descemetoceles, and perforated corneal ulcers with conjunctival autografts in small animals usually halts progression and initiates healing of the corneal ulcer, transplants epithelium, fibroblasts and blood vessels to a weakened cornea, and maintains vision.

Conjunctival autografts Conjunctiva to conjunctiva Conjunctival autografts are used infrequently, because canine and feline conjunctival defects usually heal by secondary intention, and transposition to other areas in the same eye or between eyes is seldom indicated. Nevertheless, destruction of large areas of the conjunctiva after trauma, chemical burns, and loss after conjunctival neoplasm excision may require transposition of conjunctival tissues from other conjunctival sites. Thin mucosal grafts can be easily constructed from the dorsal bulbar conjunctiva because this is the most accessible and the largest source. Most grafts are performed free-hand, because the conjunctival defects are usually irregular in shape and size. Transplantation to the ventral bulbar and palpebral conjunctival areas is more difficult, and construction of the ventral fornix requires long-term conformers. Grafts from the dorsal bulbar and palpebral conjunctivae are more convenient. The upper conjunctival fornix provides primarily for ocular mobility, but not for the collection and maintenance of tears. Conjunctival autografts are performed under general anesthesia and routine surgical preparation of the eyelids and conjunctival surfaces. Conjunctival grafts must be thin and devoid of most of the underlying connective tissues. Most conjunctival grafts are either free-hand island or pedicle types. Pedicle grafts are preferred if sufficient adjacent

164

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Fig. 7.9 An autogenous pedicle bulbar conjunctival graft is used to cover significant defects following tumor excision. (a) Preparation of the site in the dorsolateral conjunctiva to receive an autogenous pedicle conjunctival graft. The surgical defect resulted from previous excision of a hemangioma. The adjacent area for the pedicle bulbar conjunctival autograft is outlined. (b) Completion of the pedicle conjunctival graft. The graft edges are apposed with 5-0 to 7-0 simple interrupted absorbable sutures.

conjunctiva is available. Mucous membrane grafts should be free of pigmentation. The conjunctival graft site must be carefully prepared, and any necrotic or potentially infected tissues removed. The adjacent bulbar conjunctiva is incised by small tenotomy scissors to produce a pedicle flap to cover the surgical defect (Fig. 7.9a). The thin conjunctival pedicle should be 1–2 mm larger than the graft site to compensate for graft shrinkage. As the scissors undermine and separate the conjunctival mucosa from Tenon’s capsule, the scissors’ tips should be plainly visible when the graft is sufficiently thin. Once fitted to the graft site, the edges of the graft and conjunctival mucosa are carefully apposed to ensure epithelium to epithelium apposition with 5-0 to 7-0 simple interrupted absorbable sutures (Fig. 7.9b). A partial temporary tarsorrhaphy can be used to decrease eyelid trauma, and provide pressure to facilitate apposition of the graft to the underlying Tenon’s capsule.

Buccal mucosa autografts to conjunctiva The buccal mucosa is a nearly unlimited potential graft source for the conjunctiva. The buccal mucosa is thicker than the conjunctiva and often pigmented. In construction of buccal mucosa grafts, as much as possible of the submucosal tissues should be dissected from the graft to provide a very thin mucosa graft. Like autogenous conjunctival grafts, buccal mucosa grafts are performed free-hand, their shape and size being dependent on the conjunctival defect. After transposition, the buccal mucosa will become white for several days and pink color will gradually return as the graft revascularizes. Partial temporary tarsorrhaphies can assist with graft transposition by providing a protective cover to the graft site, and counterpressure to assist graft establishment and vascularization.

Conjunctival autografts to cornea Conjunctival autografts are frequently used in small animal ophthalmology in clinical management of deep corneal ulcers, descemetoceles, and perforated corneal ulcers (Figs 7.10–7.12). Conjunctival autografts consist of either bulbar or palpebral conjunctival mucosa with epithelium and connective tissue (fibroblasts, blood vessels, and lymphatics). These autografts can be transposed and sutured onto the

Conjunctival grafts/transplantation

Fig. 7.10 Extensive keratomalacia in a young dog. This patient is a candidate for a conjunctival autograft.

Fig. 7.11 Deep central corneal ulcer in a brachycephalic dog. Note the steep sides of the corneal ulcer and the lack of corneal vascularization. A conjunctival autograft is recommended.

Fig. 7.12 Central descemetocele in a brachycephalic dog. The center of the corneal defect is clear and did not retain topical fluorescein. A conjunctival autograft is recommended.

cornea to provide additional support and tissue for a cornea weakened by deep ulceration, descemetocele, or perforation with or without iris prolapse. The transplanted conjunctival autograft provides additional tissues and no risk of host rejection. Conjunctival autografts provide sufficient tissue to strengthen a weakened cornea and prevent staphyloma formation. If additional strength is indicated, a frozen section of sterile cornea or sclera is positioned in the corneal defect before the conjunctival graft is applied. Conjunctival grafts provide new and often highly viable epithelium. When harvested from the limbal area, the transplanted

conjunctival epithelium is also a stem cell capable of additional generation and transition into corneal epithelium. The conjunctival autograft contains blood vessels and lymphatics to offer significant antibacterial, antifungal, antiviral, antiprotease, and anticollagenase effects. With conjunctival transplants, leukocytes, antibodies, serum, and a2-macroglobulin (thought to be the anticollagenase factor) are immediately incorporated into the corneal ulcer bed. Because of the conjunctival blood vessels, systemic antibiotics can enter the ulcer site in higher levels. The fibrovascular or deeper layer of the conjunctival transplant offers immediate fibroblasts and collagen to begin rebuilding the corneal stroma (Fig. 7.13). Conjunctival autografts from either bulbar or palpebral conjunctiva should be thin, and not include Tenon’s capsule or the bulbar fascia. The inclusion of Tenon’s capsule creates a thicker than necessary graft, and may contribute to surgical failure by increasing tissue contraction and tension by the transplanted conjunctiva. The scar will be more prominent with a thick autograft. Transpalpebral conjunctival autografts contain limited portions of the fibrous tarsal layer which may be necessary to maintain the graft base from the deeper aspects of the eyelid to the corneal surface. As a general guide, if the surgeon can visualize the ophthalmic scissors beneath the conjunctival graft as it is being prepared, the graft is sufficiently thin. Conjunctival autografts are more difficult to perform than nictitating membrane flaps, but are easier than corneoconjunctival and corneoscleral transpositions, and the different types of keratoplasty procedures. Conjunctival autografts are indicated for progressive and medically non-responsive corneal ulcers, fungal corneal ulcers, deep stromal corneal ulcers, descemetoceles, ’leaking’ corneal ulcers (positive Seidel test), perforated corneal ulcers, and perforated corneal ulcers with iris prolapse. Some ophthalmic instrumentation is essential to perform these grafts and usually includes: an eyelid speculum, Beaver No. 6400 or 6700 microsurgical blade, Beaver scalpel handle, small tenotomy or Steven’s scissors, both small serrated and 1  2 teeth thumb forceps to handle the conjunctiva, ophthalmic needle holder usually with a lock (to accommodate 5-0 to 7-0 ophthalmic sutures), and suture tying thumb forceps. Some magnification (5–10) for the operative procedure is highly recommended. There are several different types of conjunctival autograft (Table 7.1). The divisions are based on the source of the mucosa (bulbar, tarsopalpebral, or corneoconjunctival) and the type of graft (advancement, bridge, complete, island (free), or pedicle). The dorsal bulbar conjunctiva is the most frequent source of mucosa, because of its accessibility and large surface area. The transpalpebral graft is usually constructed from the upper eyelid and sufficient tissue is available for any size corneal defect. Generally, the more central the corneal defect, the more critical the conjunctival grafting procedure. The different types of conjunctival autograft have different clinical characteristics that influence their clinical use (Table 7.2). The larger the surface area of the cornea covered by the conjunctival graft, the greater the postoperative impairment to patient’s vision, the greater the barrier to postoperative intraocular examination, and, at least theoretically, the greater impediment for the corneal and intraocular

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A

B

Fig. 7.13 (a) Descemetocele in a dog treated by a pedicle conjunctival graft (6 weeks postoperative). (b) Pedicle bulbar conjunctival graft in a cat with a deep stromal corneal ulcer (immediate postoperative).

Table 7.1 Types of conjunctival autograft for corneal defects

Position of corneal defect

Type of conjunctival autograft

Peripheral

Paracentral

Central

Corneoconjunctival, bulbar

Sliding/pedicle

þþþ

þþ

þ

þþþ

þþ

þþ

Complete (360 )

þ

þþ

þþþ

Island

þ

þþþ

þþþ

Pedicle

þþþ

þþþ

þþþ

Island

þ

þþþ

þþþ

Pedicle

þ

þþþ

þþþ

Advancement (hood)


Tarsopalpebral

þþþ most used; þþ occasionally used; þ infrequently used.

Table 7.2 Clinical characteristics of conjunctival grafts

Type of graft Characteristics

Advancement

Bridge

Complete

Island (bulbar/TP)

Pedicle (bulbar/TP)

Barrier to eye exam

Partial

Partial

Total

Partial

Partial

Barrier to eye drugs

Minor

Minor

Major

Minor

Minor

Difficult to perform

Low

Moderate

Moderate

Low

Moderate

Dehiscence potential

Low

Low

Medium

Medium

Medium

Maintenance of viability

High

High

High

Moderate

Moderate

Obstructs vision

No

Little

Total

Little

Little

Surgical trauma

Low

Moderate

High

Little

Moderate

Suture patterns

Simple

Simple

Simple and mattress

Simple

Simple

TP, tarsopalpebral.

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Conjunctival grafts/transplantation

penetration of most ophthalmic drugs. In those types of graft used to cover the central cornea, and for the more serious corneal ulcers, these techniques are often more difficult to perform. Attachment of the conjunctival graft to the progressive central corneal ulceration must be exact. Magnification provided by a head loupe or preferably the operating microscope is necessary for those types of conjunctival autograft that are apposed by sutures directly to the adjacent corneal epithelium and stroma. Preparation for surgery for the different types of conjunctival autograft is similar. Once under general anesthesia, the eyelids are carefully clipped and the eyelid skin prepared for surgery. The conjunctival surfaces are carefully cleaned of any debris with sterile cotton-tipped applicators. Dilute solutions of 0.5% povidone–iodine are used to treat the surfaces of both the conjunctiva and cornea to reduce the overall microbial population, and then rinsed from the eye with sterile saline. A lateral canthotomy may be indicated to increase exposure of the surgical site and facilitate the surgery for most dogs except the brachycephalic breeds.

Complete (360
) bulbar conjunctival autograft (Gundersen type) The complete, 360
, or Gundersen-type conjunctival autograft has been used extensively in veterinary ophthalmology since its first description nearly 50 years ago, but has now been partly replaced by conjunctival grafts that only partially cover the cornea. In this graft nearly all of the bulbar conjunctiva is separated from the underlying Tenon’s capsule to cover the entire cornea. The graft covers the corneal defect but is not apposed directly by sutures. Because the entire cornea is covered, patient vision, examination of the

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eye, and the intraocular penetration of topical drugs through both the vascularized mucosa and the cornea is reduced. With this graft, systemic as well as topical administration of drugs is recommended. Of all of the different types of conjunctival graft, the complete 360
conjunctival graft provides the maximum support for the entire cornea. Corneal defects involving the central and paracentral areas of the cornea are treated with this type of conjunctival graft. For the 360
fornix-based conjunctival graft, the dorsal bulbar conjunctiva is elevated by fine teeth thumb forceps and incised by scissors at the limbus (Fig. 7.14a). The bulbar conjunctiva is separated from the underlying Tenon’s capsule by alternating blunt–sharp dissection by small tenotomy scissors with blunt tips. For a reasonably thin conjunctival graft, the scissors’ tips should be easily observed through the thin mucosa (Fig. 7.14b). To facilitate dissection, saline can be injected subconjunctivally to help separate the bulbar conjunctiva from Tenon’s capsule. Some hemorrhage is expected and depends on the extent of conjunctival hyperemia associated with the corneal ulceration and secondary iridocyclitis. If the surgical dissection plane enters Tenon’s capsule, additional hemorrhage results. The bulbar conjunctiva is dissected for 360
about the limbus. The most difficult area is usually under the nictitating membrane (Fig. 7.14b). As the cornea measures about 15  16 mm in the dog, and 16  17 mm in the cat, in vertical and horizontal diameters, respectively, adequate amounts of bulbar conjunctiva necessitate 8–10 mm of dissection from the limbus for 360
. As the different rectus muscles in the dog and cat insert 6–10 mm from the limbus, preparation of the conjunctival graft requires surgical dissection immediately beneath the bulbar conjunctiva and not on the sclera.

C

D Fig. 7.14 In the 360
, or Gundersen-type, conjunctival graft, (a) The dorsal bulbar conjunctiva is elevated by fine 1  2 thumb forceps and incised by tenotomy scissors. (b) A thin bulbar conjunctival graft is constructed by careful separation from the underlying Tenon’s capsule. The tips of the tenotomy scissors should be visible under the conjunctival mucosa. The bulbar conjunctiva is incised at the limbus for 360
and separated from Tenon’s capsule for approximately 10–12 mm posterior to the limbus. (c) Once the bulbar conjunctival graft has been constructed, its dorsal and ventral edges are apposed with 5-0 to 7-0 absorbable simple interrupted or simple mattress sutures, or a combination of both suture patterns. (d) Once completed, the 360
bulbar conjunctival graft covers the entire cornea.

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Modified complete (360
) bulbar conjunctival graft with two suture lines

Fig. 7.15 A complete bulbar conjunctival graft 4 weeks postoperatively. The entire cornea was covered by bulbar conjunctival mucosa, but this is now retracting and several sutures are missing.

The conjunctival graft must be thin to minimize traction and excessive pressure on the sutures postoperatively. When properly prepared, the loosened edges of the bulbar conjunctival graft should rest on the central cornea and not retract spontaneously to the limbus. The edges of the bulbar conjunctiva are apposed horizontally with 5-0 to 7-0 absorbable simple interrupted or simple mattress sutures (Fig. 7.14c). Usually four to six sutures are necessary to appose the dorsal and ventral conjunctival edges. Simple interrupted mattress sutures are recommended if the graft is thicker than desirable or additional traction on the suture line is anticipated. A pursestring stitch has also be used but is not recommended as this produces additional tension on the graft as all edges are pulled to the center of the cornea. Once completed, the 360
bulbar conjunctival graft covers the entire cornea (Fig. 7.14d). The transposed conjunctival mucosa is not usually sutured directly to the corneal defect, but can be if perforation is likely or the deep corneal ulcer is already leaking aqueous humor (Fig. 7.15). As these grafts completely cover the cornea, vision in the eye is obscured and intraocular inspection is not possible.

A

B

The complete or 360
bulbar conjunctival graft has been modified to include two suture lines instead of a single suture line. The major reason for failure of the complete or 360
bulbar conjunctival graft is the premature retraction of the conjunctiva from the central cornea, and the failure of the sutures to hold the dorsal and ventral conjunctival edges together. In this technique a ‘relief incision’ of the dorsal bulbar conjunctiva is performed to lessen the ‘pressure’ on the sutures apposing the upper and lower edges of the graft. In this technique, a wide 10–15 mm strip of dorsal bulbar conjunctiva is prepared by incisions at the dorsal limbus for 180
, and parallel to the limbus 10–15 mm for 180
(Fig. 7.16a). Beyond the second incision, additional bulbar conjunctival mucosa is separated from Tenon’s capsule to eventually slide ventrally toward the limbus. The conjunctival graft must be thin and the tips of the curved blunt-tipped tenotomy scissors should be clearly visible through the thin graft. The surgical plane is in the subconjunctival fascia above Tenon’s capsule to avoid the deeper dorsal extraocular muscle insertions. Both edges of the wide strip of dorsal bulbar conjunctiva are apposed to the adjacent loosened conjunctiva by 5-0 to 7-0 simple interrupted absorbable sutures (Fig. 7.16b). The ventral 180
of the bulbar conjunctiva is prepared as described in the previous procedure to separate at least 8–10 mm of thin ventral conjunctival mucosa from Tenon’s capsule (Fig. 7.16c). The presence of a double rather than a single suture line substantially reduces the likelihood of suture failure, but increases the time required to prepare this graft.

Advancement (hood or 180
) bulbar conjunctival graft The advancement (hood or 180
) bulbar conjunctival graft is very similar to the complete 360
technique, except that only the dorsal or lateral bulbar conjunctiva is transposed onto the cornea. This method is most useful for dorsal and lateral paracentral and peripheral corneal defects. Advancement bulbar conjunctival grafts are difficult, but

C

Fig. 7.16 The modified complete bulbar conjunctival graft is a modified very wide bridge graft. (a) In the modified complete bulbar conjunctival graft, a wide strip (10–15 mm) of dorsal bulbar conjunctiva is constructed by tenotomy scissors. The bulbar conjunctival graft should be sufficiently thin to permit visualization of the scissors’ tips through the mucosa while performing the initial 360
peritomy starting at the limbus. (b) The dorsal aspects of the dorsal bulbar conjunctival graft are positioned over the center of the cornea and apposed to the limbus with 5-0 to 7-0 simple interrupted absorbable sutures. The remaining exposed surgical wound thereby provides a relief incision. (c) The ventral edge of the wide strip of dorsal bulbar conjunctiva is apposed with 5-0 to 7-0 simple interrupted absorbable sutures to the edge of the ventral bulbar conjunctiva. Hence, with two lines of sutures instead of a single row to appose the complete bulbar conjunctival graft, and the 10–15 mm from the relief incision, the possibility of general suture failure and dehiscence is reduced.

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Conjunctival grafts/transplantation

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B

C

Fig. 7.17 Most advancement (hood or 180
) bulbar conjunctival grafts are performed in the dorsal or lateral quadrants because of accessibility. (a) The bulbar conjunctiva is incised at the limbus with small tenotomy scissors and separated for 180
from the underlying Tenon’s capsule. (b) The advancement bulbar conjunctival graft is positioned over the paracentral corneal defect, and its edges apposed to the corneal defect and adjacent areas with 5-0 to 7-0 simple interrupted absorbable sutures. (c) Postoperative appearance of an advancement or hood conjunctival graft several weeks after surgery. As this graft does not obscure vision, it can be left permanently in situ.

not impossible, to prepare from the medial bulbar conjunctiva beneath the nictitating membrane or from the ventral bulbar conjunctiva. Advancement grafts permit patient vision and intraocular examinations, and appear to impact minimally on corneal and intraocular drug penetration. If the advancement graft has limited-to-no impact on vision and the central cornea, it may be left permanently in position. The dorsal or lateral bulbar conjunctiva is incised by small curved blunt-tipped tenotomy scissors at the limbus for 180–200
and dissected toward the conjunctival fornix for about 10–12 mm (Fig. 7.17a). The bulbar conjunctiva is separated primarily by blunt dissection from the underlying Tenon’s capsule, and should be sufficiently thin to allow visualization of the scissors’ tips under the mucosa. The graft is manipulated to cover the corneal defect without excessive traction, and apposed to the central edge of the corneal ulcer with 5-0 to 7-0 simple interrupted absorbable sutures (Fig. 7.17b). Additional sutures are positioned along the leading edge of the conjunctival graft to the cornea to provide additional support for the graft and decrease the possibility of suture failure at the corneal ulcer site. One or more additional sutures can be added to attach the conjunctival graft to other areas of the corneal defect, especially at the limbus. Conjunctival graft adhesion will occur only at the corneal ulcer site. Once suture removal occurs, the areas of the conjunctival graft covering the cornea with epithelium will not adhere. Depending on the pre-existing disease, advancement bulbar conjunctival grafts usually do not interfere with vision and can be left permanently in situ (Fig. 7.17c). An example is use of a permanent advancement graft to strengthen the postoperative corneoscleral wound after excision of a limbal or epibulbar melanoma in a dog or cat.

bulbar conjunctival graft is recommended for central, dorsal paracentral, and lateral paracentral corneal defects. The bridge of conjunctiva is usually prepared from the dorsal bulbar conjunctiva because of its accessibility and quantity. Two parallel bulbar conjunctival incisions are performed by small curved blunt-tipped tenotomy scissors at the limbus and about 10–12 mm toward the conjunctival fornix (Fig. 7.18a). The conjunctival graft should be sufficiently thin to permit visualization of the scissors underneath. The bridge of bulbar conjunctiva is manipulated across the cornea and its edges apposed to the underlying corneal defect and adjacent normal cornea with 5-0 to 7-0 simple interrupted absorbable sutures. Additional sutures may be used about the corneal defect to ensure graft adherence to the corneal ulcer edges and base (Fig. 7.18b). Often a temporary partial tarsorrhaphy is also used to prevent excessive lid trauma to the graft and its suture, but still accommodate topical medication and limited vision.

Pedicle bulbar conjunctival graft Pedicle bulbar conjunctival grafts are becoming more popular in small animal ophthalmology because of their minimal effect on vision, intraocular examination, and drug penetration into the anterior segment. Their preparation is not difficult, but adequate corneal bed preparation is critical. All suspect necrotic corneal tissue must be excised by sharp dissection from the corneal ulcer to ensure graft apposition to the ulcer base and edges, and for maintenance of the surrounding sutures. The pedicle graft must be of sufficient size to cover the entire corneal ulcer; it is usually constructed 1–2 mm wider than the diameter of the corneal defect.

Bridge bulbar conjunctival graft The bridge (or bipedicle) bulbar conjunctival graft is a further modification of the complete bulbar conjunctival graft with two suture lines. The approximate width of this bridge of bulbar conjunctiva should be 10 mm or more to ensure its vitality. As the bridge of dorsal bulbar conjunctival mucosa is perfused at both ends, ischemia of the graft is less likely than with pedicle grafts. Sutures may be used to attach the corneal defect to the bridge of conjunctival mucosa. As with the other incomplete conjunctival grafts, the impact on vision, intraocular examination, and corneal and intraocular drug penetration is only partial. The bridge

A

B

Fig. 7.18 Bridge bulbar conjunctival graft. (a) A 10 mm or wider strip of thin dorsal conjunctiva is constructed with small tenotomy scissors. The dotted lines indicate the extent of the bridge of mucosa. (b) After placement on the cornea, the bridge bulbar conjunctival graft is apposed to the corneal defect and other edges of the graft to the cornea by 5-0 to 7-0 simple interrupted absorbable sutures.

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B

D

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Fig. 7.19 Pedicle bulbar conjunctival graft. (a) The corneal ulcer is carefully debrided to remove all suspect necrotic and/or infected tissues. (b) The dorsolateral bulbar conjunctiva is most accessible and the graft’s base is usually lateral or at the 12 o’clock position. The dotted line indicates the outline for the pedicle graft. (c) A pedicle strip of thin bulbar conjunctiva is prepared primarily by small tenotomy scissors. (d) After preparation of the bulbar conjunctival pedicle graft, its end is trimmed by scissors to conform to the ventral edge of the corneal ulcer. The pedicle graft should lie flat on the corneal surface, and be neither stretched nor excessive in length. (e) The entire tip of the pedicle is apposed to the corneal ulcer by 5-0 to 7-0 simple interrupted absorbable sutures. At least one suture is carefully positioned between the dorsal edge of the corneal ulcer and the pedicle; this suture is positioned along the long axis of the graft to minimize its effect on the graft’s blood supply.

Pedicle bulbar conjunctival grafts may be used for central, paracentral, and peripheral corneal defects. The recipient bed for the pedicle graft is prepared in the corneal ulcer. Debridement of the ulcer’s edges and base with the Beaver No. 64 blade should remove all necrotic tissues (Fig. 7.19a). The tissues are usually transparent to opaque and partially liquefied or very soft. The pedicle graft is usually prepared from the dorsal bulbar conjunctiva because of improved exposure. The size and shape of the pedicle are outlined on the dorsolateral bulbar conjunctiva (Fig. 7.19b). The pedicle edges include the dorsolateral limbus and toward the fornix. The pedicle should be approximately 1–2 mm wider than the corneal defect. The pedicle base is constructed to be slightly wider than its tip to ensure adequate perfusion of the pedicle’s tip. The bulbar conjunctiva is incised and separated from the underlying Tenon’s capsule by alternating blunt–sharp dissection by small curved blunt-tipped tenotomy or Steven’s scissors

Fig. 7.20 Three-week postoperative appearance of an established bulbar conjunctival pedicle graft in a dog.

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(Fig. 7.19c). Once prepared, the conjunctival pedicle graft is placed on the cornea and its tip trimmed to match the edge of the ventral corneal defect (Fig. 7.19d). The pedicle graft should not be stretched or excessively slack, and rotated less than 45
from the vertical. A single suture is placed along the long axis of the pedicle graft in the dorsal corneal defect edge to ensure contact between the corneal ulcer base and the graft. The remaining tip of the pedicle graft and then the sides are gradually spread and apposed directly to the corneal defect edges with 5-0 to 7-0 simple interrupted absorbable sutures (Fig. 7.19e). The conjunctival wound created by the construction of the conjunctival pedicle graft is apposed with 5-0 to 7-0 simple interrupted absorbable sutures (Fig. 7.20).

Pedicle tarsopalpebral conjunctival graft Pedicle tarsopalpebral conjunctival grafts from the upper eyelid offer another source, the tarsopalpebral conjunctiva, for an autogenous mucosa transplant for corneal defects. The pedicle of the tarsopalpebral conjunctiva is directly apposed to the central corneal defect. This method may be used when dorsal bulbar conjunctiva is not available or diseased. As movement between the eye and upper eyelid is unavoidable, a partial temporary tarsorrhaphy for 2–4 weeks is recommended after placement of the tarsopalpebral conjunctival graft. The corneal ulcer is carefully debrided to remove all the potentially necrotic tissues and prepare a bed for the conjunctival graft. The upper eyelid is grasped and everted with a chalazion or entropion clamp (Fig. 7.21a). The clamp facilitates graft construction and provides hemostasis. The

Conjunctival grafts/transplantation

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Fig. 7.21 Tarsopalpebral conjunctival graft in the dog or cat. (a) The upper eyelid is clamped and everted with a chalazion forceps. A small transpalpebral conjunctival graft is prepared by incision with the Beaver No. 6400 blade. (b) The tarsopalpebral conjunctival graft is apposed to the central corneal ulcer by at least three 5-0 to 7-0 simple interrupted absorbable sutures. After apposition of the graft to the corneal ulcer, a partial temporary tarsorrhaphy is performed to cover the graft and reduce eyelid movements.

tarsoconjunctiva is incised to prepare a pedicle graft that is about 1 mm larger than the corneal defect. The length of the pedicle graft should be sufficient to span the corneal surface and upper eyelid without traction and restriction of eyelid movements. The tarsopalpebral conjunctiva is elevated from the underlying tarsus and orbicularis oculi muscle layer by sharp dissection with a scalpel or tenotomy scissors. The tarsopalpebral conjunctival graft with the epithelial layer exposed is attached to the corneal defect with at least three 5-0 to 7-0 simple interrupted absorbable sutures (Fig. 7.21b). The sutures should be placed to a depth of one-half to two-thirds thickness of the viable cornea surrounding the graft. A partial temporary tarsorrhaphy may be used to restrict eyelid movement, but still allow topical medication, patient vision, and eye examinations. Excessive manipulation of the eyelids postoperatively should be avoided.

postoperative period as with the other conjunctival grafts. Like the other partial conjunctival grafts, preservation of the patient’s vision, unimpaired drug penetration into the cornea and anterior segment, and postoperative eye examinations are facilitated. However, unlike the other conjunctival grafts, improvement of blood supply of the corneal ulcer area is not rapid, which may be very important in septic corneal ulcers. The surgical technique is quite simple. The corneal ulcer is carefully debrided and all possible necrotic tissues excised. With the upper eyelid everted and clamped with a 9 mm chalazion clamp, a circular section of transpalpebral conjunctiva is harvested by a razor blade held by the Castroviejo blade breaker (Fig. 7.22a). An alternative procedure utilizes dorsal bulbar conjunctiva. Incision with the Beaver No. 6400 microsurgical blade is usually less satisfactory. The graft’s base is undermined at the level of the mid tarsus with Steven’s tenotomy scissors (Fig. 7.22b). The graft should be about 10% larger than the corneal wound to compensate for graft shrinkage. After trimming to conform to the wound shape, the tarsoconjunctival graft is apposed to the corneal wound with either 8-0 to 9-0 nylon or simple interrupted absorbable sutures (Fig. 7.22c). Critical to the success of this type of graft is the meticulously closely placed sutures; often 15–20 sutures are employed for exact apposition between the free graft and the corneal wound edges (Fig. 7.23). The palpebral or bulbar conjunctival wound is allowed to heal by secondary intention. Without a blood supply, island grafts will rapidly blanch and remain white until vascularization from the cornea occurs within 10–14 days. Graft subsistence is apparently derived from the adjacent corneal stroma, aqueous humor, and tears. Central island grafts in corneas with no or very limited vascularization require additional time for the vascular supply to develop to the graft.

Corneoconjunctival autograft Island tarsopalpebral conjunctival graft Island tarsopalpebral conjunctival grafts have been used in dogs and cats. The free or island grafts have been useful for the surgical management of deep corneal ulcers, descemetoceles, and corneal perforations. These grafts with no blood supply are apposed directly to central or paracentral corneal defects. There is no need to trim these grafts in the

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The corneoconjunctival graft is a modified sliding conjunctival graft that transplants adjacent peripheral cornea and the attached bulbar conjunctiva into the central corneal wound. Another modification is corneoscleral transposition in which the adjacent cornea and sclera are shifted into a corneal defect. These methods permit transplantation of autogenous cornea from an adjacent healthy area in the

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Fig. 7.22 Island or free transpalpebral conjunctival graft. (a) An 8–9 mm circular section of tarsopalpebral conjunctiva is incised from the upper eyelid, grasped and clamped by a chalazion forceps. (b) The graft is separated from the deeper layers of the tarsus by scissors. The graft should be 1 mm larger than the corneal defect to compensate for tissue shrinkage. (c) The island tarsopalpebral conjunctival graft is apposed to the edges of the carefully debrided corneal ulcer by 15–20, 8-0 to 9-0 simple interrupted sutures with either non-absorbable or absorbable material. These sutures are meticulously placed to prevent any interruptions between the graft and corneal ulcer surfaces.

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Fig. 7.23 One month postoperative appearance of an island or free transpalpebral conjunctival graft in a dog. Both graft and cornea contain numerous blood vessels.

Fig. 7.24 Corneal sequestrum involving the deeper corneal stroma in a short-haired domestic cat. After excision of the sequestrum, the corneal defect will be filled with a corneoconjunctival transposition.

same eye and usually yield less central corneal scarring. Their use in infected and progressive bacterial corneal ulcers should be delayed until the infectious and melting (protease) process has been resolved. Their use in fungal infected corneas is not recommended. Transposition of a normal healthy cornea into an infected environment will not be successful. Corneoconjunctival transposition has been used successfully for treatment of deep corneal ulceration, descemetocele, and feline corneal sequestration affecting the deeper layers of the cornea (Fig. 7.24). Corneoscleral transposition is indicated for full-thickness defects of the cornea and is presented in Chapter 8. After surgical preparation and placement of a lightweight eyelid speculum, a lateral canthotomy is performed to improve exposure. The corneal ulcer site is carefully

debrided to remove all potentially infected and/or necrotic tissue. Often the corneal bed is enlarged 1 or 2 mm for adequate removal of all suspect tissues. The sliding graft of cornea and conjunctiva is then prepared. Extending from the corneal wound dorsally, two partial-thickness, slightly diverging corneal incisions are created by the Beaver No. 6400 microsurgical blade (Fig. 7.25a). Once the limbus is traversed, the dissection plane is altered to subconjunctiva, and the bulbar conjunctiva is incised by the scalpel blade or small tenotomy scissors. The edge of the corneal transposition is elevated by small thumb forceps, and, by sharp dissection with the Beaver No. 6400 microsurgical blade or a corneal lamellar knife-dissector, the corneal epithelium and about one-half of the thickness of the stroma are

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D Fig. 7.25 Corneoconjunctival transposition. (a) The corneal bed is carefully prepared to remove any diseased tissues. Two slightly diverging corneal stromal incisions with the Beaver No. 6400 blade are extended dorsally to the limbus. (b) The pedicle of anterior corneal stroma and epithelium is carefully separated from the deeper stroma by sharp dissection. (c) The dissection is continued by small tenotomy scissors between the bulbar conjunctiva and Tenon’s capsule for a sufficient length to accommodate ventral sliding into the corneal defect. (d) The end and sides of the corneoconjunctival pedicle are apposed by 5-0 to 7-0 simple interrupted absorbable sutures.

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Conjunctival grafts/transplantation

Fig. 7.26 One-month postoperative appearance of a corneoconjunctival graft. The portion of the graft at the center of the cornea will remain clear.

carefully incised to the limbus (Fig. 7.25b), usually using the base of the corneal defect as a reference. The dissection is continued by scissors into the subconjunctival space, separating the bulbar conjunctiva from the underlying Tenon’s capsule (Fig. 7.25c). When the subconjunctival attachments of the conjunctival mucosa have been separated, the entire graft can be positioned into the corneal defect and trimmed, if necessary, to fill the corneal wound. The transplanted cornea should be 0.5–1 mm wider than the corneal defect to compensate for shrinkage of the grafted corneal tissue. The edges of the entire corneoconjunctival graft are carefully apposed to the corneal wound with 5-0 to 7-0 simple interrupted absorbable sutures (Figs 7.25d and 7.26).

Postoperative patient management, success rates, and potential complications The postoperative management of all of the conjunctival grafts is similar. Often a partial temporary tarsorrhaphy is used at the conclusion of the graft procedure to reduce eyelid trauma to the surgical site, reduce exposure, provide pressure on the graft site, permit topical medication, allow patient vision, and facilitate daily ophthalmic examinations. An E-collar or other restraint device is also recommended to prevent self-trauma to the eye and surgical site by the small animal patient. Although inconvenient, these protective collars should be worn by the patient for approximately 2 weeks or until the conjunctival graft appears well established. Topical medications are directed at the corneal ulcer, tear film proteases, and secondary anterior uveitis. Topical and often systemic antibiotics are administered to either treat corneal sepsis or prevent secondary corneal infection. Topical mydriatics, such as 1% atropine, are instilled a few times to initiate and maintain mydriasis, but prolonged and excessive topical atropine can reduce tear production by 50% or more. Topical antiproteases such as autologous serum and/ or EDTA are used to reduce tear film protease activity to allow for faster healing. Tear film proteases will attack absorbable sutures to cause premature graft retraction. Topical and systemic treatments are usually administered for 5–10 days; thereafter only topical medications are continued until the graft is established. Topical antibiotics/ corticosteroids and/or cyclosporine may be administered about 20–30 days postoperatively to reduce corneal scarring and pigmentation. Suture removal is generally not necessary unless nonabsorbable sutures are employed. The complete,

advancement, and pedicle conjunctival grafts are usually trimmed and the limbal base severed by scissors under topical anesthesia about 4–6 weeks postoperatively. Trimming of the conjunctival graft that is adherent to the corneal wound is not usually necessary unless excessive and protruding mucosa are present. In time, these conjunctival grafts will gradually conform to the corneal curvature, and the majority will become pigmented. The success rates for conjunctival grafts in all animal species are quite high. In one study in which 90% of the conjunctival grafts were pedicle, the overall success rate in dogs as judged by structural integrity of the cornea was 91%. The success rate for the free or island tarsopalpebral conjunctival graft in dogs and cats was 98%. There are several reasons for conjunctival graft failures and most are related to: 1) technique; 2) inadequate corneal wound preparation; and 3) aqueous humor leakage under these grafts (Box 7.1). Adequate corneal wound debridement cannot be overemphasized, as the presence of necrotic and infected tissues within the corneal bed can contribute to graft dehiscence. Bacterial wound infections of the surgical site and suture failures are infrequent. Aqueous humor appears toxic to conjunctival fibroblasts; leakage of aqueous humor under these grafts causes graft thickening and seems to prevent permanent apposition of the graft to the base of the corneal wound. Seidel’s tests should be performed pre- and postoperatively to detect corneal perforations. Circumferential sutures placed at one-half to two-thirds thickness of the cornea seem to offer the best technique to minimize this complication. Sutures within a conjunctival graft should be placed radially and along the long axis of the pedicle graft not only to avoid blood vessel occlusion, but also to provide the optimum apposition of the graft to the corneal wound. In deep or perforated corneal ulceration, failure of a conjunctival graft should not prevent the placement of another conjunctival graft to maintain corneal integrity and hopefully preserve vision.

Permanent conjunctival grafts Conjunctival grafts are usually employed as temporary transplants to strengthen a weakened cornea. Within 4–6 weeks, the base of the conjunctival graft is severed. However, the advancement and pedicle bulbar conjunctival grafts may be left in position permanently with their bases not transected for selected chronic and/or recurrent conditions, such as keratoconjunctivitis sicca and feline corneal sequestration.

Box 7.1

Causes of conjunctival graft failures

1. Incomplete corneal site preparation and debridement of necrotic and/or septic tissues 2. Incomplete covering of the surgical site 3. Aqueous humor leakage from deep or perforated corneal ulcers 4. Graft direction is greater than 45
from the vertical 5. Excessive stretching of the graft 6. Wound infection 7. Suture and/or knot failure 8. Infarction of conjunctival graft vessels

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Depending on the size and position of the conjunctival graft and pupil size, vision may still be present. The persistent corneal edema in phthisis bulbi (results from intraocular pressure below 5 mmHg) and corneal endothelial dystrophy (results from defective corneal endothelia) can be permanently and totally covered by a thin complete bulbar conjunctival graft. These grafts can reduce corneal edema, prevent the formation of painful vesicles, and, if thin enough, can permit limited clinical vision in small animals.

Substitute materials for conjunctival grafts There are patients in which adequate and viable conjunctiva may not be available for grafting to corneal defects. Most of these patients have had previous conjunctiva and/or lid surgeries, and the dorsal conjunctiva is scarred or of inadequate amount to perform the surgery. Pedicle bulbar grafts may be constructed from the ventral conjunctiva, but the surgery is more difficult and the amount of available conjunctiva quite limited. Fortunately, there are both experimental and commercially available alternatives. These include the porcine small intestinal submucosa (SIS) graft which is available commercially, and the amniotic graft, available experimentally. Both grafts have been covered with pedicle conjunctival grafts in some patients while in other patients they are the sole ‘patch’ to cover the corneal defect. Both grafts seem to tolerate placement in uncontrolled septic corneal ulcers; in these patients covering these avascular grafts with a pedicle bulbar conjunctival graft is recommended.

Porcine small intestinal submucosa (SIS) grafts The SIS graft provides a scaffold for corneal healing as well as additional strength to the overlying bulbar conjunctival graft. Rabbit corneal SIS graft studies suggest that the graft collagen sheet is actually incorporated into the healing process. The SIS graft is derived from the porcine jejunum and is composed of three distinct layers: 1) tunica muscularis mucosa; 2) tunica mucosa; and 3) the stratum compactum layer of the tunica mucosa. Following processing and mechanical debridement, a few remaining endothelial cells and fibrocytes are lyzed with a hypotonic wash, leaving a sheet of collagen with a smooth surface (stratum compactum) and a rough surface (tunica muscularis mucosa). The SIS graft is sterilized by ethylene oxide, and supplied commercially as either 7  10 mm sheets, or 10 mm and 15 mm diameter ophthalmic discs. The SIS graft is a biomaterial consisting primarily of proteins and, to a lesser extent, carbohydrates and lipids. Closer analyses of the SIS graft indicate that it has ideal qualities for corneal replacement and healing, and consists of collagen (types I, III, and VI), glycosaminoglycans (hyaluronic acid, chondroitin sulfate A and B, heparin, and heparin sulfate), and other glycoproteins (fibronectin), as well as fibroblastic growth factor (FGF-2) and transforming growth factor b (TGF-b). The SIS graft is acellular, biodegradable, non-immunogenic, and xenogeneic. By providing a scaffold for healing, the results are more like regeneration, rather than replacement and scar formation. In rabbits

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and dogs, after lamellar corneal transplantation with SIS grafts, re-epithelialization occurred after 7 and 14 days, respectively. After debridement of the septic corneal ulcer, the SIS graft is carefully trimmed and ‘fitted’ to cover in excess of 1– 1.5 mm of the entire corneal ulcerative bed. After securing the graft to the ulcer’s edges with several 7-0 to 9-0 simple interrupted absorbable sutures, the entire SIS graft is covered with a bulbar pedicle conjunctival graft. SIS grafts have been reported in dogs, cats, rabbits, and horses. SIS grafts have been reported to fill the limbocorneal defect after limbal melanocytoma excision and covered with bulbar conjunctiva, for full-thickness corneal ulcerative disease in dogs and covered with conjunctival grafts, after corneal ulcers and corneal sequestra in cats and not covered with conjunctival grafts, and after corneal ulceration and corneal stromal abscess formation in horses and covered with conjunctival grafts. These grafts are convenient to use, are commercially available and ready for use, avoid potential virus transmission as is possible with feline-based grafts, and are easy to handle during surgery. If placed in an uncontrolled septic corneal ulcer, covering with a conjunctival graft is highly recommended. If used alone and successful, it appears that the SIS graft-treated corneal defects are more translucent than those treated with pedicle bulbar conjunctival grafts.

Amniotic grafts as conjunctival substitutes Amniotic grafts have been reported to repair deep corneal ulcers in horses and for experimentally induced full-thickness corneal defects dogs. The amniotic grafts for both the horse and dog studies were harvested from normal equine placenta and are not available commercially. In the dog study, after harvest, the amniotic grafts were preserved in 98% sterile glycerol (full-thickness scleral grafts are commonly preserved in glycerol). The equine amniotic graft is obtained aseptically as a 5 mm2 section of amnion after death or cesarean section. After harvest, the tissues are preserved in 98% sterile glycerol; immediately before use the tissue is rehydrated in sterile saline solution.

Other tissues for conjunctival substitutes The equine pericardium has also been used in surgery to correct canine lateral canthal entropion, deep corneal ulcerations in dogs, fill the orbital cavity of dogs after enucleation, and as a scleral graft. Equine renal capsule grafts have also been used to cover large corneal defects in dogs.

Adaptations in large animals and special species Conjunctival grafts or flaps are used frequently in equine ophthalmology for the clinical management of deep, melting, and large corneal ulcers, descemetoceles, and for perforated corneal ulcers with and without iris prolapse. Conjunctival flaps are best mobilized from the bulbar conjunctiva. We do not recommend using the conjunctiva near the nictitans, as nictitans movement postoperatively can put tension on the graft and result in premature graft release. Conjunctival grafts can be

Adaptations in large animals and special species

transposed and sutured onto the cornea to provide sufficient tissue to strengthen most weakened corneas, but are not as strong as corneal grafts (Fig. 7.27). Conjunctival autografts contain limbal stem cells, blood vessels, and lymphatics to offer significant antibacterial, antifungal, antiviral, antiprotease, and anticollagenase effects. With conjunctival grafts, polymorphonuclear leukocytes, antibodies, serum, and a2macroglobulins are immediately placed in the corneal ulcer bed. Systemic antibiotics can enter the ulcer site in higher levels through leakage from the conjunctival graft vasculature. The fibrovascular or deeper layer of the conjunctival transplant offers immediate fibroblasts and collagen to begin rebuilding of the corneal stroma. Conjunctival grafts usually result in various sizes and degrees of corneal scars. Scarring can be minimized by removal of necrotic cornea by keratectomy prior to graft placement. Postoperative topical corticosteroids can reduce this postoperative scar tissue formation to a minimum, but corneal scarring after conjunctival grafts should be anticipated. Conjunctival autografts are more difficult to perform than nictitating membrane flaps, but are simpler than corneoconjunctival and corneoscleral transpositions, and penetrating

keratoplasty surgeries. They are easier to perform in the horse than in other species as the horse has a great deal of very mobile conjunctiva. To perform optimal conjunctival grafts in horses, general anesthesia is recommended. Magnification using a head loupe, head-mounted telescope or the operating microscope is recommended. Ophthalmic instruments and suture sizes are identical to those in small animals. Conjunctival autografts from either bulbar or palpebral conjunctiva should be thin, and should not include Tenon’s capsule or the bulbar fascia. Tenon’s capsule should be stripped or cut from the graft such that the graft lies over the corneal defect prior to suture placement. The inclusion of Tenon’s capsule may contribute to surgical failure by increasing the traction on the transplanted conjunctival graft. Conjunctival flaps should have tension-relieving sutures placed at the limbus to prevent the graft pulling off the ulcer bed prematurely. Conjunctival pedicle grafts utilizing bulbar conjunctiva from the dorsal or temporal quadrants are my preference as the conjunctiva in those areas is surgically available, and the pedicle flaps cover only the ulcer surface to allow postoperative observation of the pupil and anterior chamber as the graft does not

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Fig. 7.27 Examples of bulbar conjunctival grafts in the horse. (a) Acute corneal ulceration with central descemetocele in a young Thoroughbred foal. Note the diffuse corneal edema and peripheral corneal vascularization. (b) Same eye 2 weeks postoperatively after successful treatment with a pedicle bulbar conjunctival graft. The ocular and corneal inflammation have markedly regressed. (c) Postoperative appearance (4 weeks) of a combination of bridge (horizontal) and pedicle (6 o’clock position) bulbar conjunctival grafts in an adult horse with a deep central corneal ulcer. (d) Three day postoperative appearance of a dehisced or failed pedicle bulbar conjunctival graft in a deep corneal ulcer infected with a combination of b-Streptococcus and Pseudomonas spp. in a adult horse. The loose end of the unsuccessful pedicle graft as well as the remaining corneal absorbable sutures are still present.

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cover the entire cornea. If possible, melting ulcers should be stabilized with medical therapy prior to graft placement in order to prevent protease digestion of absorbable sutures holding the conjunctival graft in place. Temporary tarsorrhaphies are performed concurrently with conjunctival grafts to minimize blinking movements to the corneal sutures and allow quick graft adherence to the stroma.

Surgery for aberrant conjunctival overgrowth in rabbits Aberrant conjunctival overgrowth, pseudopterygium or precorneal membranous occlusion is a recently described conjunctival disease which appears unique to this species. The disease is characterized by proliferation of the bulbar and palpebral conjunctiva in a circular manner which eventually nearly totally occludes the corneal surface (Fig. 7.28). This aberrant conjunctiva does not adhere to the cornea. It can affect one or both eyes in young and adult rabbits, and the dwarf breeds may be predisposed. Surgeries used to treat this condition include: 1) simple resection; 2) repositioning of conjunctiva to the limbus; 3) dividing the aberrant conjunctiva into medial and lateral portions, and relocation to the fornix; and 4) centrifugal incisions of the aberrant conjunctiva to the limbus and transpalpebral fixation of the conjunctiva. In the last technique, the conjunctival overgrowth is divided into six more-or-less equal sections and incised to the limbus. With simple mattress non-absorbable sutures placed through the base of the eyelid, the tip of each conjunctival section is retracted into the conjunctival fornix. Postoperative treatment usually consists of topical antibiotics and corticosteroids for several days. Topical cyclosporine may delay or prevent recurrence. The transpalpebral method of fixation of the aberrant conjunctiva to the conjunctival fornix seems the most effective procedure at this time.

SURGERIES OF THE NICTITANS Surgeries of the nictitans are common in small animal practice, and may be used to treat primary nictitans diseases, as well as diseases of the adjacent conjunctiva and cornea. Excision of the entire nictitans is not recommended except for

Fig. 7.28 Rabbit with aberrant conjunctiva. The proliferative conjunctival overgrowth is attached at the limbus but is not adhered to the conjunctiva, and totally surrounds the cornea.

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generalized and advanced third eyelid neoplasia. In the past 10–15 years, several surgical procedures have evolved to treat the prolapsed nictitans gland or ’cherry eye’, and preserve as much as possible tear production in the dog. Surgeries of the nictitans in horses and cattle most often involve neoplasia. Squamous cell carcinomas are the most frequent neoplasms in both species, and with the often considerable involvement the entire nictitans must be removed. In addition, neoplasia of the nictitans of both of these species has a greater tendency to infiltrate the deeper orbital tissues and necessitate exenteration of the entire orbit.

Surgical treatment of everted nictitans Occasional malformations of the nictitating membrane cartilage occur, usually resulting in eversion of its leading margin (Fig. 7.29). Infrequently, the abnormality results in an inversion or an inward scroll-like deformity of the cartilage. The condition usually presents unilaterally, but bilateral involvement may occur eventually. Eversion of the third eyelid cartilage usually affects the large and giant breeds of dogs, including the Great Dane, St Bernard, German Shepherd, Weimaraner, Newfoundland, German Shorthaired Pointer, many retriever breeds, and English Bulldog. Inheritance has been suggested in the German Shorthaired Pointer. Eversion of the nictitating membrane cartilage may also occur after trauma and surgery. Eversion of the nictitans usually occurs in dogs during the first year of life. The condition also occurs in cats. Clinical signs consist of a raised pink deformity of the medial canthus, which upon closer inspection is the curled nictitans with its posterior leading margin exposed. Secondary chronic conjunctivitis and epiphora may be present. The defect affects the upper portion of the stem of the T-shaped cartilage resulting in a U-shaped abnormality that reflects forward from the leading margin of the nictitans (Fig. 7.30). Microscopic examination of affected areas of the cartilage reveals no abnormalities, although this area is probably the weakest part of the cartilage. Suggested cause(s) include prominence of the nictitans, cartilage defect, and adherent conjunctival surfaces.

Fig. 7.29 Eversion of the nictitating membrane in a Great Dane puppy. With eversion of the leading margin, the posterior or bulbar aspect of the nictitans becomes visible.

Surgical treatment for hyperplastic lymphoid follicles

Fig. 7.30 Curled section of the hyaline cartilage excised to treat eversion of the nictitating membrane. Scale in millimeters.

Surgical treatment for eversion of the nictitating membrane cartilage consists of local excision of the affected cartilage without disturbing the pigmented margin (Fig. 7.31a). Surgical trauma to the pigmented margin may result in the loss of pigment to this area. After excision of the ’curled’ cartilage, the leading margin of the nictitating membrane should re-establish in its normal position and conform to the corneal curvature (Fig. 7.31b). After general anesthesia, the corneal and conjunctival surfaces are carefully cleansed with sterile cotton-tipped applicators and the area irrigated with 0.5% povidone–iodine.

The eyelid hair is not usually clipped. After draping, the nictitating membrane is protracted by thumb forceps, being careful to avoid the leading margin. A small linear incision through the bulbar surface of the mucosa is performed with small tenotomy scissors directly over the involved cartilage (Fig. 7.32a). By careful blunt–sharp dissection, the scroll-like section of the nictitating membrane cartilage is removed (Fig. 7.32b). The surgical wound is not usually apposed and is allowed to heal by secondary intention. If apposition by sutures is preferred, a 50 to 7-0 simple continuous suture or simple interrupted absorbable sutures are placed submucosally and the knots buried to avoid suture contact with the cornea. The immediate postoperative appearance is usually a slightly swollen but normal-appearing nictitating membrane (Fig. 7.32c). Postoperative medical treatment consists of topical antibiotics/ corticosteroids several times a day for 5–7 days. Recurrence after surgical correction is most unlikely.

Surgical treatment for hyperplastic lymphoid follicles Limited numbers of lymphoid follicles occur normally on the deep or bulbar surface of the nictitating membrane. In chronic inflammation there may be abundant numbers of lymphoid follicles on both surfaces (Fig. 7.33). Mechanical debridement of excessive lymphoid follicles with dry cotton gauze or a blunt scalpel blade is sometimes indicated if topical antibiotic/corticosteroid therapy has been unsuccessful. Use of silver nitrate or

Fig. 7.31 Results of surgical correction of the everted nictitating membrane in a dog. (a) Preoperative appearance of an everted nictitating membrane in a German Shepherd dog. (b) Immediate postoperative appearance after excision of the affected cartilage portion.

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Fig. 7.32 Technique for surgical correction of the everted nictitating membrane. (a) To correct the everted nictitating membrane, the nictitans is protracted to expose its bulbar (deep) surface. With tenotomy scissors, a small linear incision is made through the mucosa directly over the affected cartilage. (b) By blunt–sharp scissor dissection, the scroll-like section of cartilage is isolated and excised. (c) With the defective area of cartilage removed, the nictitating membrane leading margins will return to normal position.

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Fig. 7.35 Protrusion of the gland of the nictitating membrane in a young Miniature Poodle dog. Note the smooth surface of the prolapsed gland.

Fig. 7.33 Excessive lymphoid follicles on the bulbar (deep) surface of the nictitating membrane.

copper sulfate crystals to chemically destroy these follicles is not recommended because additional conjunctival and/or corneal damage may result if these compounds contact their surface. After topical anesthesia, the nictitating membrane is protracted with thumb forceps to expose the excessive lymphoid follicles on the palpebral and/or bulbar surfaces. With a blunt scalpel blade or a section of dry surgical sponge wrapped around a small curved hemostat, the surface is vigorously rubbed to rupture and remove the follicles (Fig. 7.34). Limited hemorrhage may occur. After scraping of the lymphoid follicles, topical antibiotics/corticosteroids are usually administered three or four times a day for several days.

Surgical procedures for protrusion of the gland of the nictitating membrane or ’cherry eye’ Protrusion of the gland of the nictitating membrane is not infrequent in dogs and most affected animals are less than 1 year of age (Fig. 7.35). Although usually presented with a unilateral protrusion of the nictitans gland, the condition may eventually become bilateral. The condition occurs most commonly in the American and English Cocker Spaniel, English Bulldog, Beagle, Pekingese, Boston Terrier, Basset

Fig. 7.34 To remove most of the lymphoid follicles, carefully scrape the area with a dull Beaver No. 6400 microsurgical blade.

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Hound, Lhasa Apso, and Shih Tzu. The condition occurs infrequently in young cats and mainly in the Burmese breed. Although protrusion and prolapse of the nictitating membrane gland is a relatively common condition in the dog, the pathogenesis of the condition has not been determined.

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Is the adenitis primary to the development of the gland enlargement and protrusion or secondary? Are fascial abnormalities present that attach the cartilage and/or gland to the periorbital fascia and predispose to the condition? Are specific pathogens involved in this adenitis? With protrusion and enlargement of the third eyelid gland, are there simultaneous changes occurring in the lacrimal gland?

The occurrence of keratoconjunctivitis sicca in dogs after this condition would certainly suggest that both the lacrimal and the nictitans tear glands are eventually involved. As the pathogenesis of the protrusion of the nictitating membrane gland is revealed, medical and/or surgical treatment strategies may become further refined. Protrusion of the superficial gland of the nictitating membrane results from hypertrophy and hyperplasia of the gland sufficient to extend beyond the leading margin of the nictitans (Fig. 7.36). Secondary epiphora, conjunctivitis, an obvious mass at the medial canthus, and local irritation are the usual presenting clinical signs (Fig. 7.37). Microscopic examination of affected glands usually reveals dacryoadenitis, but detailed studies and isolates for viral and other pathogens have not been reported.

Fig. 7.36 Protrusion of the gland of the nictitating membrane in a Boston Terrier dog as viewed from its posterior surface. Part of the swollen gland extends from the base of the nictitans.

Surgical procedures for protrusion of the gland of the nictitating membrane or ’cherry eye’

Box 7.2 •

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Fig. 7.37 Chronic protrusion of the gland of the nictitating membrane in a mixed breed dog. Note the lymphoid follicles on the surface of the swollen gland.

Topical antibiotics or antibiotic/corticosteroid therapy may be used to treat early and mild cases. Reduction in the local inflammation and edema of the conjunctiva may result in the gland returning to its normal size and position. Unfortunately, topical medical treatment is often unsuccessful, and surgical treatment of the prolapsed gland of the nictitans is necessary. The standard procedure for surgical treatment of the prolapsed third eyelid gland prior to about 1980 was conservative excision of the prolapsed portion of the gland to preserve as much as possible of this important tear source. As indicated earlier, the gland of the nictitating membrane in both the dog and cat provides about 25–40% of the total tears. Although protrusion of the nictitating membrane gland and keratoconjunctivitis sicca occur in many breeds of dogs, the interrelationships of these two conditions is poorly understood. One study involving 33 dogs with protrusion of the third eyelid gland for at least 2 years that had had either excision (partial) of the nictitans gland or surgical replacement, suggested that keratoconjunctivitis sicca developed in 48% of the eyes treated by excision of the gland, in 43% of the eyes with prolapsed glands left untreated, and in 14% of the eyes treated with surgical replacement of the gland. In the most frequently affected breeds, i.e., American Cocker Spaniel, Lhasa Apso, and English Bulldog, keratoconjunctivitis sicca developed in 47.3% of all affected eyes: 59% of eyes treated by gland excision, 17% of eyes treated with gland replacement, and 75% of eyes with the nictitans gland left prolapsed. Several procedures have been developed to treat protrusion of the nictitating membrane and still retain this tear gland (Box 7.2). These methods may be arbitrarily divided into those that retract or anchor the prolapsed gland via its cartilage, and those that cover (envelope or imbrication) the prolapsed gland with adjacent mucosa to force it into a normal position. Those methods that attempt to anchor the cartilage and retract the prolapsed gland prevent normal movements and protraction of the nictitating membrane. The surgical procedures that incise the bulbar (or deep aspects) of the nictitating membrane surface and cover the prolapsed gland with adjacent conjunctival mucosa risk

Surgical procedures for replacement of the canine prolapsed gland of the nictitating membrane

Posterior nictitans anchoring or tacking approach – To ventral oblique muscle (Albert, Garrett, Whitley) – To ventral equatorial sclera (Gross) – To ventral periorbital fascia (Blogg) Anterior nictitans anchoring or tacking approach – To ventral periorbital rim (Kaswan and Martin) Intranictitans anchoring of glands (Plummer et al) Imbrication or mucosa envelope: scarification and cover with adjacent conjunctival mucosa (Moore) Envelope or mucosa pocket: cover with adjacent mucosa (Morgan/Moore)

direct damage to the ducts of the third eyelid gland, and have generally been replaced by the anterior approach. The excretory ducts of the nictitans gland exit the gland and emerge in the middle section of the bulbar mucosa surface. Hence, any surgical technique to treat this condition should have three goals: 1) adequately replace the prolapsed gland behind the nictitans leading margin; 2) result in no postoperative limitations on nictitating membrane movements; and 3) produce no damage or loss of glandular tissues including the excretory ducts. One method may not achieve all of these goals equally nor be effective in treating all degrees of third eyelid gland protrusion: those procedures that effect anchoring the nictitans cartilage more deeply may be more successful for the more extensive and chronic gland prolapses; the pocket methods may be more effective in puppies and for mild protrusions of the third eyelid gland. The surgical procedures will be divided based on entry to the prolapsed nictitans gland: 1) from the posterior or bulbar surface of the nictitans to anchor the cartilage base to the ventral epibulbar fascia, ventral equatorial sclera, or ventral oblique muscle; 2) from the anterior or palpebral surface of the nictitans to anchor the nictitans cartilage to the periosteum of the orbital rim; 3) intranictitans anchoring or tacking of the gland; and 4) partial-to-complete covering of the prolapsed gland with adjacent conjunctival mucosa (pocket and imbrication methods). For all of these surgical procedures, surgical preparation is limited. After the onset of general anesthesia, the eyelid hair is not usually clipped, but thoroughly cleansed with surgical soap and irrigated with sterile saline. The conjunctival and corneal surfaces are cleansed with sterile cotton-tipped applicators to remove any exudates and debris, and rinsed with 0.5% povidone–iodine solution. A small wire eyelid speculum is placed to retract the eyelids.

Posterior (bulbar) nictitans anchoring approach For the posterior nictitans anchoring approach, the posterior conjunctival fornix behind the nictitating membrane is incised, an anchor suture is positioned into the deeper fascial or ocular tissues, and the gland is retracted by suture. The anchoring suture retracts the prolapsed gland into position, but prevents normal nictitans movements thereafter.

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Surgical procedures for the conjunctiva and the nictitating membrane

Recent studies indicate that the posterior surface of the nictitans gland contains ductules from the underlying secretary gland; therefore, to maintain tear secretion, the nictitans gland and its posterior surface should not be separated. Also, the posterior methods are more difficult to perform than the anterior approach, and the anchoring suture is more likely to retract from the orbital or globe base. As a result, the anterior methods are more popular. In the anchoring procedures by Blogg, Gross, and others, the nictitating membrane is protracted by thumb forceps to expose its deep or bulbar surface and the prolapsed gland (Fig. 7.38a). By Bard–Parker No. 15 scalpel or Beaver No. 6400 microsurgical blade, an incision is made starting at the limbus and extending to the posterior aspects of the prolapsed gland (Fig. 7.38b). The gland is thoroughly separated from its conjunctival and periorbital fascial attachments by blunt-tipped tenotomy scissors. The globe is then rotated by thumb forceps to expose the bulbar conjunctival fornix. By blunt dissection with tenotomy scissors, the deeper

aspects of the incision are exposed to reveal the ventral sclera close to the equator of the globe, the ventral oblique muscle, or strong periorbital fascia (Fig. 7.38c). A 4-0 monofilament nylon (or other non-absorbable) suture with a cutting needle is placed through the dorsal portion of the gland and then 6–10 mm into the peribulbar area to anchor to the ventromedial equator, periorbital fascia, or the ventral oblique muscle (Fig. 7.38d). The more extensive the nictitans gland protrusion, the deeper the site for the anchoring suture. As the suture is tied, the gland should return to its approximate normal position (Fig. 7.38e). The conjunctival mucosa incision is apposed with a 5-0 to 6-0 simple continuous absorbable suture (Fig. 7.38f,g). A modification of this procedure reduces the possibility of disturbing the gland and its posterior ductules, but is more difficult. The initial incision extends from the ventromedial limbus to the posterior aspects of the gland, and then is continued to encircle the gland’s posterior surface (Fig. 7.39a). Using tenotomy scissors, the gland is isolated

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Fig. 7.38 Posterior nictitans anchoring method for treating gland protrusion. (a) The bulbar surface of the nictitans is exposed to reveal the extent of the gland prolapse. (b) The mucosa is incised by a Beaver No. 6400 microsurgical blade from posterior of the gland to the medioventral conjunctival fornix and then to the limbus. Unfortunately, this may damage the majority of the nictitans gland’s ducts. (c) The basal portion of the gland and the nictitans cartilage are carefully separated from their fascial attachments by scissor dissection. By blunt dissection with tenotomy scissors, the anchor site (the ventral sclera, ventral oblique muscle or periorbital fascia) is isolated. (d) A 4-0 green monofilament nylon suture with a reverse-cutting needle is passed through the prolapsed portion of the gland and the anchor site. (e) As the suture is tightened and tied, the gland should return to its original position. (f) The conjunctival mucosa is apposed with a 5-0 to 6-0 simple continuous suture. The knots are buried to prevent corneal contact. (g) Cross-section of the completed surgery: (A) eyelid; (B) nictitans cartilage; (C) nictitans’ tear gland; (D) orbital bony rim; (E) deep anchor of the green non-absorbable suture.

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Surgical procedures for protrusion of the gland of the nictitating membrane or ’cherry eye’

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Fig. 7.39 A modification of the posterior anchoring procedure attempts to retain as much of the prolapsed gland posterior mucosa and secretory ductules as possible. Because of the limited surgical exposure, large prolapses may not be candidates for this procedure. (a) The initial conjunctival incision by a Bard– Parker No. 15 scalpel blade extends from the ventromedial limbus to encircle the prolapsed gland. (b) The fascial attachments beneath the gland that attach to the stem of the nictitans cartilage are carefully transected by blunt scissor dissection. The ventral sclera, periorbital fascia or the ventral oblique muscles are also isolated. (c) A 4-0 green monofilament nylon suture with a cutting needle is used to encircle the gland and its deep orbit anchor. (d) As the suture is tied, the gland should shift to deep within the posterior nictitans fornix. (e) The conjunctival wound is closed with the nictitans gland posterior mucosal surface within its center with several 5-0 to 6-0 simple interrupted absorbable sutures. The knots of these sutures should not touch the cornea.

and the deeper ventral sclera exposed (Fig. 7.39b). A 4-0 monofilament nylon suture with a cutting needle is carefully positioned in the dorsal aspects of the prolapsed gland and then into the ventromedial equator, periorbital fascia, or ventral oblique muscle (Fig. 7.39c). As the knot is tied, the gland is positioned deep in the posterior conjunctival fornix (Fig. 7.39d). The conjunctival wound is apposed with the prolapsed gland and its mucosa in its center with several 5-0 to 6-0 simple interrupted absorbable sutures (Fig. 7.39e). The knots should not touch the corneal surface.

Anterior nictitans anchoring approach The anterior nictitans anchoring technique differs from the posterior anchoring technique by using the conjunctival fornix in front of the nictitans or the medial lower eyelid. The suture is still embedded beneath the conjunctival mucosa over the nictitans gland. If the anchoring point is more anterior of the current nictitans base, as the suture to retract the gland is tightened the nictitans may be displaced more anteriorly. In this approach, the nictitans is protracted by forceps to expose its palpebral surface and the palpebral conjunctival fornix at its base. A ventral linear incision of the anterior mucosa of the nictitans is performed with small tenotomy scissors (Fig. 7.40a). A 3-0 to 4-0 monofilament nylon suture is carefully placed in the periosteum of the ventromedial orbital rim and then directed dorsally to exit the top of the prolapsed nictitans gland (Fig. 7.40b). The suture is reintroduced into its exit hole and directed to the opposite side of the top of the prolapsed gland (Fig. 7.40c). The suture is then redirected into its second exit hole to emerge in the incision (Fig. 7.40d). As the suture is tied, the prolapsed gland should gradually

return to its normal position behind the leading margin (Fig. 7.40e). The conjunctival wound is apposed with a 5-0 to 6-0 simple continuous suture (Fig. 7.40f,g).

Intranictitans tacking procedure This new procedure, developed by the Florida veterinary ophthalmologists, utilizes the suture anchoring technique around the entire nictitans tear glands, but limits the surgery (essentially placement of a single suture) to only the nictitans, thereby permitting nictitans movements postoperatively. Imperative in this procedure is the base of the nictitans cartilage when the single suture enters and exits the nictitans, thereby providing an excellent strong base to anchor to the gland. This suture must pierce and not encircle the shaft of the nictitans cartilage during its insertion and egress to avoid the small blood vessels which parallel the shaft’s sides. This procedure involves no conjunctival mucosal incisions, and does not restrict nictitans movements postoperatively. A 4-0 nylon suture with a three-eighths circle 13 mm reverse P-3 cutting needle is passed from the anterior surface of the third eyelid through the base of the cartilage to the posterior aspect and tunneled circumferentially beneath the conjunctiva over and around the prolapsed nictitans gland. The suture is then passed back through the base of the cartilage shaft to the anterior surface of the nictitans. It is gradually tightened to compress the prolapsed gland into its normal position and tied with a surgeon’s knot (Fig. 7.41).

Conjunctival mucosa envelope procedure The conjunctival mucosa may be used to cover the prolapsed nictitans gland permanently and apply pressure to

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Surgical procedures for the conjunctiva and the nictitating membrane

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Fig. 7.40 Anterior nictitans anchoring (or tacking) technique. (a) The nictitans is protracted by thumb forceps to expose its palpebral (anterior) surface and the conjunctival fornix. A linear incision of the conjunctival mucosa is performed by small tenotomy scissors. (b) A 3-0 to 4-0 green monofilament nylon suture with a reverse-cutting needle is secured first in the periosteum of the ventromedial orbital rim and then directed dorsally to exit at the top of the gland. (c) Through the same suture hole, the needle is reinserted to exit at the opposite side of the gland. (d) The suture is then reinserted again to exit in the incision. (e) As the suture is tightened and tied, the prolapsed gland should return to its original position. (f) The conjunctival mucosal wound is apposed with a 5-0 to 6-0 simple continuous absorbable suture. (g) As viewed in cross-section, the suture is secured in the distal position of the prolapsed nictitating membrane gland and ventral periorbital fascia or the periosteum of the ventral orbital rim. Lower eyelid (A), cartilage of the nictitans (B), prolapsed gland of the nictitating membrane (C), the ventral orbital bony rim (D), and the deep anchor of the nylon suture (E).

maintain the gland protrusion behind the leading margin of the nictitating membrane. The imbrication or envelope method has been reported to be most successful for young puppies (10–12 weeks old) and for acutely prolapsed nictitans glands that are not large. The mucosa over the prolapsed gland is lightly scarified with a Bard–Parker No. 15 scalpel or Beaver No. 6700 microsurgical blade (Fig. 7.42a). The more extensive the scarification, the greater the permanent adhesions that develop postoperatively. With a 6-0 to 7-0 absorbable suture, two 4 mm bites on the ventral aspects of the gland and a larger 6–8 mm bite on the dorsal side of the prolapsed gland is performed (Fig. 7.42b). As the suture is tied, a sterile cotton-tipped applicator is used to depress the gland as the conjunctival mucosa is pulled over the prolapsed gland.

Conjunctival mucosa pocket procedure The conjunctival pocket method is recommended for older dogs and for chronic prolapses of the nictitans gland. Some

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veterinary ophthalmologists use this technique for all nictitans gland prolapses. In this procedure, the adjacent conjunctiva is incised into two 120–140
sections and apposed by sutures over the prolapsed gland. The open ends of the two conjunctival flaps allow the nictitans gland’s tears to continue to exit onto the corneoconjunctival surfaces. The nictitating membrane is protracted by thumb forceps to reveal the bulbar surface and the prolapsed gland (Fig. 7.43a). With the Beaver No. 6400 microsurgical blade, the mucosa above (about 2–3 mm from the leading margin) and below (next to the prolapsed gland and toward the bulbar conjunctival fornix for 6–10 mm) the prolapsed gland is incised for about 1 cm (120–140
). The ends of the two incisions should not connect to each other (Fig. 7.43b). The conjunctival mucosa overlying the prolapsed gland is left undisturbed. After careful dissection of the submucosa layer about both incisions by tenotomy or Steven’s scissors, the conjunctival incisions are apposed with a 5-0 to 6-0 simple continuous absorbable suture (Fig. 7.43c). If the tension

Surgical procedures for protrusion of the gland of the nictitating membrane or ’cherry eye’

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Fig. 7.41 Intranictitans tacking technique for nictitans prolapsed gland. (a) The 4-0 green nylon suture with a three-eighths circle 13 mm reverse P-3 cutting needle is first placed through the base of the cartilage of the third eyelid. (b) The suture is tunneled subconjunctivally around the gland on the posterior face of the nictitans. The needle must exit and re-enter the subconjunctival space at each corner for proper placement of the suture around the gland. (c) With the same suture exit and re-entry sites, no suture is exposed to irritate the corneal surface. (d) With the suture around the gland, the suture is passed back through the nictitans cartilage to its anterior surface. (e) The two ends of the suture are carefully tightened and tied to achieve the desired reduction of the prolapsed gland. (f) Side view of the prolapsed gland with its anchoring suture through the nictitans cartilage. (Reproduced with permission from Plummer CE, Ka¨llberg ME, Gelatt KN et al 2008 Intranictitans tacking for replacement of prolapsed gland of the third eyelid of dogs. Veterinary Ophthalmology 11:228–233.)

on the suture appears extensive because of a large glandular prolapse, 4-0 to 5-0 simple interrupted absorbable sutures are recommended. The knots are carefully buried to avoid corneal contact. Both ends of the incisions are left open to accommodate continued tear production by the nictitans gland (Fig. 7.43d,e).

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Fig. 7.42 The conjunctival mucosa envelope procedure is used to treat prolapsed nictitating membrane glands in young puppies. (a) The mucosa over the gland protrusion is lightly scarified by scraping with the Bard–Parker No. 15 scalpel or Beaver No. 6700 microsurgical blade. (b) With a 6-0 to 70 absorbable suture, two 4 mm bites of mucosa ventral of the gland and a single 6–8 mm bite anterior to the gland are used to appose the mucosa.

Postoperative treatment and complications Postoperative therapy after these procedures to reposition the gland of the nictitating membrane usually consists of topical antibiotics or antibiotics/corticosteroids three to four times daily until the prolapsed gland has reduced to about normal size, and supplemented for several days with an oral non-steroidal anti-inflammatory, such as carprofen (4 mg/kg PO q24h; RimadylW; Pfizer Animal Health, Exton, PA), and an E-collar or other restraint device. The surgical procedures that anchor the prolapsed nictitans gland to the retrobulbar sites are more difficult because of the more limited exposure, and may exhibit more lid or conjunctival swelling. With prolapsed glands that are chronic and large, the swelling within the gland may require several weeks to approximate normalcy. Long-term postoperative problems associated with the anterior and posterior anchor methods include entropion, restriction of movements by the nictitans, and re-prolapse if suture failure occurs or the anchor site is inadequate. Anchoring to the anterior periosteum has been associated with a mild anterior displacement of the nictitans base. Long-term postoperative complications after the envelope and pocket procedures avoid suture and/or wound failure

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Fig. 7.43 Conjunctival mucosa pocket procedure to treat nictitans gland protrusion. (a) The nictitans is protracted by thumb forceps to reveal its bulbar (deep) surface and the affected gland. (b) Two semicircular (140–160
) mucosal incisions are performed with the Bard–Parker No. 15 or Beaver No. 64 blade. (c) After separation from the submucosa, the two edges of the mucosa are pulled over the gland and apposed with a 5-0 to 6-0 simple continuous absorbable suture. (d) With both ends of the conjunctival mucosa open (see arrows), secretions from the nictitans glands can exit. (e) Immediate postoperative view of a patient with conjunctival mucosal pocket procedure. Note the central continuous suture and that both ends of the ‘pocket’ are open.

when the prolapsed glands are very large, there is limited distortion and displacement of the nictitans base, and there are limited-to-no movement restrictions that are associated with the anchoring methods. Recurrence of gland prolapse after either of these two groups of procedures does not preclude an additional technique several weeks later to effect resolution. In the most recent report, using the intranictitans tacking procedure, all prolapsed glands returned to normalcy in 14 of 15 eyes. This technique, once mastered, requires little time as no tissue incisions are required. The basic histopathology of these prolapsed nictitans glands is poorly understood; however, many biopsies indicate acute dacryocystitis, with both intra- and extra-gland inflammation. The condition of the fellow tear gland in the same eye, the lacrimal gland, is unknown at this date. Dogs with prolapse of the nictitans gland and treated by these surgical procedures, only medically, or no therapy, are predisposed to keratoconjunctivitis sicca months to years later. In the study involving 33 dogs of all breeds with protrusion of the third eyelid glands for at least 2 years previously, keratoconjunctivitis sicca developed in 48% of the eyes treated by excision of the gland, in 43% of the eyes with prolapsed glands and no therapy, and in 14% of the eyes treated with these techniques to replace the gland. As a result, continued postoperative clinical monitoring of these dogs with periodic Schirmer tear tests is recommended as the development of keratoconjunctivitis sicca months-toyears after prolapse of the nictitans gland is significantly higher than in the general canine population (5.6% in dogs without gland prolapse).

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Surgical procedures for prominent/ protruded nictitans Prominent and protruding nictitating membranes are infrequent in small animals, and are usually secondary to other orbital, ophthalmic, and systemic diseases. However, occasionally in the large and giant breeds of dogs, bilateral prominent and protruding nictitating membranes occur (Fig. 7.44). In some of these animals, the defect appears more obvious by the absence of pigmentation of the nictitans leading margins. Surgical reduction of the overall size of the nictitans can be performed to not affect tear formation by the nictitans gland, maintain the integrity of the medial conjunctival fornix, and re-establish normalappearing nictitating membranes. Removal of just the leading margins of the nictitans is not recommended as the shape and the appearance of the

Fig. 7.44 Bilateral prominent nictitating membranes in a 2-year-old dog.

Nictitating membrane flaps

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Fig. 7.45 Surgical reduction of protracted nictitating membrane. (a) An enlarged nictitans can be reduced by a full-thickness excision of a section just behind the leading margin. The dotted lines are the nictitans cartilage. (b) After the full-thickness excision, the nictitans posterior and anterior surfaces are apposed with a submucosa 5-0 to 6-0 simple continuous absorbable suture and a mucosa 5-0 to 6-0 simple continuous absorbable suture, respectively.

structures are markedly altered. Total removal of the nictitating membrane will result in medial canthal disfigurement, and the development of a chronic conjunctivitis or keratoconjunctivitis because of the loss of the nictitans tear gland, and an excessively large medial conjunctival fornix. The recommended procedure to reduce the overall size of the nictitating membrane is achieved by full-thickness excision of the nictitans just below the leading margin but above the thicker portion of the cartilage that surrounds the tear gland (Fig. 7.45a). Part of the upper stem of the nictitans cartilage is removed to accommodate the reduction. Wound closure consists of two layers of simple continuous absorbable sutures involving the deeper or bulbar submucosa, and the anterior or palpebral submucosa and mucosa (Fig. 7.45b).

Nictitating membrane flaps The nictitating membrane flap has been popular for the treatment of canine and feline corneal diseases, and is relatively easily performed by most small animal practitioners. The nictitating membrane flap can be quickly performed with a minimum of ophthalmic instrumentation. The nictitating membrane is used as a flap to strengthen a weakened cornea, but generally not to graft submucosa or mucosa to corneal defects. Nictitating membrane flaps are generally indicated for neuroparalytic and neurotropic keratitis, temporary exposure keratitis, corneal erosions (Fig. 7.46), superficial corneal ulcers, after corneal laceration repair (Fig. 7.47), acute keratoconjunctivitis sicca, and for corneal vesicles associated with corneal edema (Fig. 7.48). Conjunctival grafts have largely

Fig. 7.46 The healing of a recurrent corneal erosion can be assisted by a temporary nictitating membrane flap.

Fig. 7.47 In this cat with focal corneal edema, a nictitating membrane flap can provide temporary support.

Fig. 7.48 The painful vesicles that can form with corneal endothelial dystrophy can be treated temporarily with a nictitating membrane flap.

replaced the nictitating membrane flap for the surgical treatment of deep and leaking corneal ulcerations, descemetoceles, and corneal perforations with iris prolapse. The nictitating membrane flap, used to cover the corneal surface, provides a number of benefits. The corneal surface is warmed by the flap and the increased temperature promotes higher cellular metabolic rates. The bulbar nictitans surface is rich with lymphoid follicles; scarification will provide serum, inflammatory cells, fibroblasts, and blood directly to the cornea. The nictitans flap obstructs light entering the eye and promotes mydriasis. The flap reduces the evaporation of tears from the corneal surface. It provides support to a weakened cornea and helps prevent distortion of the central cornea. The flap also protects the healing corneal epithelium from the trauma associated with normal eyelid movements.

Nictitating membrane flap–conjunctival fornix The nictitating membrane flap to cover the cornea is secured to either the dorsolateral conjunctival fornix or the dorsolateral episclera. When secured to the conjunctival fornix, extra long sutures may be used that permit occasional release to examine and treat the protected cornea. The conjunctival fornix method does not accommodate concurrent eye movements as with the episcleral technique. In the episcleral method, the securing sutures must be carefully placed and should not penetrate the sclera which may produce intraocular hemorrhage. For nictitating membrane flaps, surgical preparation is usually minimal. The eyelids are clipped and carefully cleaned with surgical soap and water for the conjunctival fornix procedure. The corneal and conjunctival surfaces are fully cleansed with sterile cotton-tipped applicators to remove all debris and exudates. Both corneal and conjunctival surfaces are rinsed with 0.5% povidone–iodine solution.

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D Fig. 7.49 Securing the nictitating membrane temporarily to the dorsolateral conjunctival fornix. (a) One tip of the thumb forceps is placed above and the other tip below the eyelid margin. The forceps tips, inserted as far as possible, indicate the position of the conjunctival fornix (arrowed) and where the sutures should traverse the eyelid. (b) The first 2-0 to 3-0 non-absorbable suture is placed through the eyelid stent (a rubber band is illustrated), through the eyelid, and into the conjunctival fornix. The needle and suture are then extended to the dorsal surface of the leading edge of the nictitating membrane to penetrate its full thickness. (c) At least two horizontal mattress sutures are pre-placed, and the part of both sutures that penetrates the leading edge of the nictitating membrane should incorporate the upper stem of the nictitans cartilage. (d) After placement of both sutures, they are tightened to secure the nictitans in the dorsolateral conjunctival fornix. Leaving the suture ends long permits occasional adjustments and lowering of the flap for inspection and medication of the eye.

Securing the nictitating membrane to the dorsolateral conjunctival fornix is the most frequent and easiest procedure using two to four interrupted mattress sutures. Old intravenous tubing, buttons, suture foam or holders, or rubber band stents can be used on the eyelid surface to distribute suture tension and prevent eyelid necrosis. All sutures must be pre-placed to ensure proper placement and tied once all are positioned. The nictitating membrane is protracted by thumb forceps and its dorsolateral movement ascertained. The extent of the dorsolateral conjunctival fornix is determined by thumb forceps with one tip above and one tip below the eyelids (Fig. 7.49a). Two to four 2-0 to 3-0 non-absorbable sutures are carefully pre-positioned through the dorsolateral eyelid and the conjunctival fornix and the leading margin of the nictitans (Fig. 7.49b). The sutures must traverse the outer portion of the leading margin to reduce its eversion, and part of at least two sutures are placed through the upper stem of the T-shaped hyaline cartilage for maximal holding ability (Fig. 7.49c). After all sutures are pre-placed, they are carefully tightened and tied (Fig. 7.49d). Often the suture ends are left long to permit occasional release to inspect and medicate the eye.

Nictitating membrane flap – Blogg and Helper modification Similar to a modification of the technique reported in a large number of cattle in the 1970s, Blogg and Helper describe a method that uses a single suture to secure the nictitans to the dorsolateral conjunctival fornix in small animals. A 2-0 double-armed suture is passed through the palpebral (or anterior) surface of the nictitating membrane

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to encircle the upper stem of the T-shaped nictitans hyaline cartilage at a point one-half to one-fourth of the distance between the leading margin and its base (Fig. 7.50a). The nictitans bulbar surface is not penetrated to avoid suture contact with the cornea. Both sutures are then passed through the dorsolateral conjunctival fornix and a rubber band or button stent. The nictitans is protracted until its leading margin is at the limbus or within the conjunctival fornix, but not so tight that compression or distortion occurs (Fig. 7.50b).

Nictitating membrane flap – episcleral fixation The nictitating membrane flap can also be secured to the dorsolateral episclera. This procedure allows simultaneous eye and nictitans movements, but is more difficult to

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Fig. 7.50 Helper–Blogg modification of the nictitating membrane flap. (a) A double-armed, single suture is used to encircle the middle portion of the stem of the T-shaped nictitans cartilage. (b) Both ends of the suture are continued to the dorsolateral conjunctival fornix and upper eyelid. A section of old intravenous tubing or rubber band stent helps distribute the suture pressure over a larger area of the eyelids.

Partial/complete excision of the nictitans

Partial/complete excision of the nictitans

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Fig. 7.51 The nictitating membrane flap can also be secured to the dorsolateral episclera and conjunctiva. (a) Two to four 1-0 to 2-0 interrupted mattress non-absorbable sutures are pre-placed full thickness behind the leading margin of the nictitating membrane and firmly in the dorsolateral episclera and bulbar conjunctiva. (b) After all sutures are positioned, they are tightened and tied.

perform. The ’holding’ power of the episclera and dorsolateral conjunctiva are more limited, and penetration of the sclera during suture placement may cause intraocular hemorrhage. The site of the dorsolateral conjunctiva and episcleral fixation to accommodate the sutures emerging from the nictitans is about 2–4 mm from the limbus. Two to four 1-0 to 2-0 simple mattress non-absorbable sutures are pre-placed through the nictitating membrane and the dorsolateral bulbar conjunctiva and episclera (Fig. 7.51a). At least one suture should be secured to the stem portion of the T-shaped nictitans cartilage. After pre-placement of all sutures, they are tightened and tied (Fig. 7.51b). Adequate suture placement in the dorsolateral bulbar conjunctiva, episclera, and Tenon’s capsule is critical to the flap’s success: sutures placed too superficial will prematurely tear from the area; sutures placed too deep may penetrate the sclera and produce intraocular hemorrhage.

Postoperative management and complications The nictitating membrane flaps are usually left in position for 10–14 days. An E-collar or other restraint device is recommended to prevent the animal damaging the eye and surgical site. Postoperative medications are directed at the underlying corneal disease, and usually include topical antibiotics and mydriatics. The thick and vascular nictitans probably impairs the delivery of many medications to the corneal surface. As a result, systemic medications are often added to those administered topically. Complications associated with nictitating membrane flaps include eyelid necrosis related to the sutures, corneal irritation from suture contact, membrane cartilage deformation, and protrusion for several days after release. Often eyelid swelling is present preoperatively and with the conjunctival fornix technique will occur postoperatively. The correct position of the nictitans flap is critical to its success with all of these techniques. If suture contact occurs with the cornea, the patient will demonstrate considerable pain and blepharospasm. Periodic postoperative examinations are recommended to check the position of the flap daily or every other day. With long sutures, the position of the nictitans flap can be adjusted to accommodate changes in the corneal disease and the eyelids.

Partial-to-complete excision of the nictitating membrane is reserved for advanced and invasive neoplasia in small animals. The most common reported nictitating membrane neoplasm in the dog is the adenocarcinoma (Fig. 7.52). In the cat, the most frequent nictitans neoplasm is the squamous cell carcinoma. Both neoplasms are locally invasive, occur most frequently in older animals, and have postoperative recurrence rates as high as 70%. Nictitating membrane neoplasms often extend both outward and inward through the periorbital fascia to gain entry into the anterior orbit. Orbital radiology and ultrasonography are recommended for nictitating membrane neoplasms to thoroughly evaluate the potential surgical site. The surgical procedure for excision of the nictitating membrane with advanced neoplasia must occasionally be converted during surgery into an exenteration. For complete excision of the nictitating membrane, the eyelid hair is clipped, and cleaned with surgical soap. The conjunctival surfaces, fornices, and the corneal surfaces are cleaned with sterile cotton-tipped applicators, and all debris and exudates removed. The corneal and conjunctival surfaces are irrigated with 0.5% povidone–iodine solution, and then rinsed with sterile saline. After placement of a small wire eyelid speculum, the nictitans is protracted and inspected carefully. Two curved hemostats are carefully placed at the base of the nictitans to slightly overlap to facilitate excision and to provide hemostasis. With Metzenbaum scissors, the nictitans is excised, including the entire cartilage and gland (Fig. 7.53a) The adjacent mucosa on each side of the hemostats is apposed with a 2-0 to 4-0 simple continuous absorbable suture (Fig. 7.53b). When a continuous suture is used, the hemostats are left in place when the suture is being positioned. Once the suture is placed, the hemostats are slowly released and retracted from the incision. The suture is then tightened and its ends tied. An alternative method does not use hemostats, but instead consists of blunt–sharp dissection by small tenotomy scissors; hemostasis is maintained by cautery and vessel ligation. For partial excision of the third eyelid, its outer portion may be excised immediately above the base of the T-shaped

Fig. 7.52 Adenocarcinoma of the nictitating membrane gland in a 10-yearold American Cocker Spaniel. Complete excision of the nictitating membrane at its base is recommended for this type of neoplasm.

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A

B

Fig. 7.53 Removing the entire nictitating membrane. (a) Two curved hemostats or Carmalt forceps are positioned and slightly overlapped at the base of the nictitating membrane, which is then excised with Metzenbaum scissors. (b) The conjunctival mucosa edges are apposed with a 2-0 to 4-0 simple continuous absorbable suture that is pre-placed loosely with the forceps in place. As the forceps is carefully removed, the sutures are tightened.

cartilage and the gland of the nictitans. This method preserves tear formation and the reduced medial lacrimal lake, but results in some disfigurement with the loss of the leading margin. The mucosa edges should be apposed to prevent exposure of the cartilage with a 5-0 to 6-0 simple continuous absorbable suture. Postoperative management after excision of the nictitating membrane consists of topical antibiotics/corticosteroids, and systemic antibiotics administered for 7–10 days. With the loss of the nictitans, tear formation should be carefully monitored and, if signs of keratoconjunctivitis sicca begin to appear, topical cyclosporine (2% solution twice daily) or oral pilocarpine (2% solution, two drops well mixed in the food twice daily for a 15 kg dog; reduce the dose for smaller animals) initiated. Because of an enlarged lacrimal lake in the medial canthus created by the loss of the nictitans, chronic conjunctivitis may develop. Intermittent administration of topical antibiotics/corticosteroids may be necessary indefinitely.

Adaptations in large animals and special species Nictitating membrane flaps provide more support to the diseased cornea than the temporary complete tarsorrhaphy in horses. Nictitating membrane flaps are used to cover and

protect a weakened cornea, but are not usually a source of tissues for the cornea. Nictitating flaps in large animals are recommended for superficial corneal diseases including corneal erosions, neuroparalytic and neurotropic keratitis, temporary exposure keratitis, and superficial corneal ulcers, and to reinforce a bulbar conjunctival graft. In one study, nictitating membrane flaps were used as an alternative to complete temporary tarsorrhaphies for the treatment of advanced infectious keratoconjunctivitis and ulcerative keratitis in 1845 cattle, with 96% success (Anderson et al). This same technique can also be used for small animals as reported by Blogg and Helper (1989; see earlier section for a description of the technique). In range beef cattle, a ‘single catch’ is often a limitation to optimal therapy; as a result, the eye examination, administering topical, subconjunctival or systemic antibiotics, and nictitating flap surgery is performed with the animal restrained in a catch chute. Absorbable sutures are preferred as, once the cow is released, re-examination and suture removal are unlikely. After a subcutaneous ring block of both eyelids and the base of the nictitans, the nictitating flap is performed using a single mattress 0 chromic gut suture (non-absorbable can also be used) with a slightly curved cutting needle. The needle is directed through the dorsolateral upper lid and into the conjunctival fornix. After exiting the lid, the needle is placed through the palpebral surface of the nictitans and under or circumventing the stem of its cartilage, just beneath its extensions. The suture is again positioned through the upper conjunctival fornix and upper eyelid and securely tied, protracting the leading margin of the nictitans onto the dorsolateral bulbar conjunctiva. With an absorbable suture, the nictitans flap will remain in position for 7–14 days. Partial-to-complete excision of the nictitans is performed not infrequently in large animals. Squamous cell carcinomas may occur in both horses and cattle, and can expand into sizeable masses, which can readily invade the deeper medial orbit. Small masses which can be manually elevated above the subcutaneous tissues may be excised; often the surgical wound is not apposed by sutures. Larger masses which invade the nictitans cartilage and gland result in total excision of the nictitans using the same procedure as in small animals.

Further reading Small animals: conjunctiva Barros PSM, Safatle AMV, Malerba TA, Burnier M Jr: The surgical repair of the cornea of the dog using pericardium as a keratoprosthesis, Brazilian Journal of Veterinary Research and Animal Science 32:251–255, 1995. Barros PSM, Garcia JA, Laus JL, Ferreira AL, Gomes TLS: The use of xenologous amniotic membrane to repair canine corneal perforation created by penetrating keratectomy, Vet Ophthalmol 1:119–123, 1998. Blogg JR, Stanley RG, Dutton AG: Use of conjunctival pedicle grafts in the management of feline keratitis nigrum, J Small Anim Pract 30:678–684, 1989.

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Bussieres M, Krohne SG, Stiles J, Townsend WM: The use of porcine small intestinal submucosa for the repair of full-thickness corneal defects in dogs, cats and horses, Vet Ophthalmol 7:352–359, 2004. Carter JD: Medial conjunctivoplasty for aberrant dermis of the Lhasa apso, J Am Anim Hosp Assoc 9:242–244, 1973. Featherstone H, Sansom J, Heinrich C: Intestinal submucosa in two cases of feline ulcerative keratitis, Vet Rec 146:136–138, 2000. Featherstone H, Sansom J, Heinrich C: The use of porcine small intestinal submucosa in ten cases of feline corneal disease, Vet Ophthalmol 4:147–153, 2001.

Gundersen T: Conjunctival flaps in the treatment of corneal diseases with reference to a new technique of application, Arch Ophthalmol 60:880–888, 1958. Hakanson NE, Merideth RE: Conjunctival pedicle grafting in the treatment of corneal ulcers in the dog and cat, J Am Anim Hosp Assoc 23:641–648, 1987. Hakanson N, Lorimer D, Merideth RE: Further comments on conjunctival pedicle grafting in the treatment of corneal ulcers in the dog and cat, J Am Anim Hosp Assoc 24:602–605, 1988. Henderson W: The repair of corneal injuries in the dog by conjunctival keratoplasty, Vet Rec 63:240–241, 1951.

Further reading Hendrix DVH: Canine conjunctiva and nictitating membrane. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 662–689. Mannis MJ: Conjunctival flaps, Int Ophthalmol Clin 28:165–168, 1988. Moore CP: Qualitative tear film disease, Vet Clin North Am Small Anim Pract 20:565–581, 1990. Moore CP: Surgery of the conjunctiva. In Bojrab MJ, editor: Current Techniques in Small Animal Surgery, ed 3, Philadelphia, 1990, Lea and Febiger, pp 18–56. Moore CP, Constantinescu GM: Surgery of the adnexa, Vet Clin North Am Small Anim Pract 27:1011–1066, 1997. Ollivier FJ, Kallberg ME, Plummer CE, et al: Amniotic membrane transplantation for corneal surface reconstruction after excision of corneolimbal squamous cell carcinomas in nine horses, Vet Ophthalmol 9:404–413, 2006. Parshall CJ: Lamellar corneal–scleral transplantation, J Am Anim Hosp Assoc 9:220–277, 1973. Peiffer RL, Gelatt KN: Complete bulbar conjunctival flap in the dog, Canine Practice 2:15–18, 1975. Peiffer RL, Gelatt KN, Gwin RM: Tarsoconjunctival pedicle grafts for deep corneal ulceration in the dog and cat, J Am Anim Hosp Assoc 13:387–391, 1977. Pirie CG, Dubielzig RR: Feline conjunctival hemangioma and hemangiosarcoma: a retrospective evaluation of eight cases (1993–2004), Vet Ophthalmol 9:227–232, 2006. Pirie CG, Knollinger AM, Thomas CB, Dubielzig RR: Canine conjunctival hemangioma and hemangiosarcoma: a retrospective evaluation of 108 cases (1989– 2004), Vet Ophthalmol 9:215–226, 2006. Roberts SR: The conjunctival flap operation in small animals, J Am Vet Med Assoc 22:86–90, 1953. Scagliotti RH: Tarsoconjunctival island graft for the treatment of deep corneal ulcers, descemetocoeles, and perforations in 35 dogs and 6 cats, Semin Vet Med Surg 3:69–76, 1988. Stern AI: Conjunctival flap operation, J Am Vet Med Assoc 117:44–45, 1950. Tsuzuki K, Yamashita K, Izumisawa Y, Kotani T: Microstructure and glycosaminoglycan ratio of canine cornea after reconstructive transplantation with glycerin-preserved porcine amniotic membranes, Vet Ophthalmol 11:222–227, 2008. Vanore M, Chahory S, Payen G, Clerc B: Surgical repair of deep melting ulcers with porcine small intestinal submucosa (SIS) graft in dogs and cats, Vet Ophthalmol 10:93–99, 2007. Wagner J, Nasisse M, Davidson M: A retrospective study of conjunctival flaps in 67 dogs and 17 horses (1987–1991), Abstract Verterinary Pathology 29:476, 1992. Williams DL: Laboratory animal ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 1336–1369.

Small animals: nictitating membrane Barnett KC: Diseases of the nictitating membrane of the dog, J Small Anim Pract 18:101–108, 1978. Blogg JR: Surgical replacement of a prolapsed gland of the third eyelid (’cherry eye’): a new technique, Aust Vet J 9:75, 1979. Bromberg NM: The nictitating membrane, The Compendium 2:627–632, 1980. Brooks DE: The canine conjunctiva and nictitans. In Gelatt KN, editor: Veterinary Ophthalmology, ed 2, Philadelphia, 1991, Lea and Febiger, pp 290–306. Constantinescu GM, McClure RC: Anatomy of the orbital fasciae and the third eyelids in dogs, Am J Vet Res 51:260–263, 1990. Dugan SJ, Severin GA, Hungerford LL, Whiteley HE, Roberts SM: Clinical and histologic evaluation of the prolapsed third eyelids gland in dogs, J Am Vet Med Assoc 201:1861–1867, 1992. Gelatt KN: Surgical correction of everted nictitating membrane in the dog, Vet Med 67:291–292, 1972. Gross SL: Effectiveness of a modification of the Blogg technique for replacing the prolapsed gland of the canine third eyelid, Transactions of the American College of Veterinary Ophthalmologists 14:38–42, 1983. Helper LC, Blogg R: A modified third eyelid flap procedure, J Am Vet Med Assoc 19:955–956, 1983. Kaswan RL, Martin CL: Surgical correction of third eyelid prolapse in dogs, J Am Vet Med Assoc 186:83, 1985. Moore CP: Imbrication technique for replacement of prolapsed third eyelid gland. In Bojrab MJ, editor: Current Techniques in Small Animal Surgery, ed 3, Philadelphia, 1990, Lea and Febiger, pp 126–128. Moore CP, Constantinescu GM: Surgery of the adnexa, Vet Clin North Am Small Anim Pract 27:1011–1066, 1997. Moore CP, Frappier BL, Linton LL: Distribution and course of ducts of the canine third eyelid gland: effects of two surgical replacement techniques, Veterinary and Comparative Ophthalmology 6:258–264, 1996. Morgan RV: To excise or not to excise, Progress in Veterinary and Comparative Ophthalmology 3:109–110, 1993. Morgan RV, Duddy JM, McClurg K: Prolapse of the gland of the third eyelid in dogs: a retrospective study of 89 cases (1980–1990), J Am Anim Hosp Assoc 29:56–60, 1993. Ojay E, Milinsky HC: Surgical correction of unpigmented prominent membrana nictitans, J Am Vet Med Assoc 144:857, 1964. Peruccio C: Surgical correction of prominent third eyelid in the dog, Calif Vet 4:24–25, 1981. Petersen-Jones S: Repositioning prolapsed third eyelid glands while preserving secretory function, J Small Anim Pract 13:202–203, 1991.

Plummer CE, Ka¨llberg ME, Gelatt KN, et al: Intranictitans tacking for replacement of prolapsed gland of the third eyelid of dogs, Vet Ophthalmol 11:228–233, 2008. Quinn AJ: Lacrimal apparatus and nictitating membrane. In Bojrab MJ, editor: Current Techniques in Small Animal Surgery, ed 3, Philadelphia, 1990, Lea and Febiger, pp 82–86. Richards DA: An adjustable suture: a technique for altering the tension of stitches postoperatively, especially in third-lid flaps, Vet Med 68:881–883, 1973. Stanley RG, Kaswan RL: Modification of the orbital rim anchorage method for surgical replacement of the gland of the third eyelid in dogs, J Am Vet Med Assoc 205:1412–1414, 1994. Startup FG: Corneal ulceration in the dog, J Small Anim Pract 25:737–752, 1984. Wilcock B, Peiffer RL: Adenocarcinoma of the gland of the third eyelid in seven dogs, J Am Vet Med Assoc 193:1549–1550, 1988.

Large animals and special species: conjunctiva and nictitans Allgoewer I, Malho P, Schulze H, Schaffer E: Aberrant conjunctival stricture and overgrowth in the rabbit, Vet Ophthalmol 11:18–22, 2008. Anderson JF, Gelatt KN, Farnsworth RJ: A modified membrana nictitans flap technique for the treatment of ulcerative keratitis in cattle, J Am Vet Med Assoc 168:706–709, 1976. Brooks DE, Matthews AG: Equine ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2007, Blackwell, pp 1165–1274. Dugan SJ: Ocular neoplasia, Vet Clin North Am 8:609–626, 1992. Dugan SJ, Curtis CR, Roberts SM, Severin GA: Epidemiologic study of ocular/adnexal squamous cell carcinoma in horses, J Am Vet Med Assoc 198:251–256, 1991. Hendrix DVH: Equine ocular squamous cell carcinoma, Current Techniques in Equine Practice 4:87–94, 2005. Kainer RA, Stringer JM, Lueker DC: Hyperthermia for treatment of ocular squamous cell tumors in cattle, J Am Vet Med Assoc 176:356–360, 1980. King TC, Priehs DR, Gum GG, Miller TR: Therapeutic management of ocular squamous cell carcinoma in the horse: 43 cases (1979– 1989), Equine Vet J 23:449–452, 1991. Lavach JD, Severin GA: Neoplasia of the equine eye, adnexa and orbit, J Am Vet Med Assoc 170:202–203, 1977. McCalla TL, Moore CP, Collier LL: Immunotherapy of periocular squamous cell carcinoma with metastasis in a pony, J Am Vet Med Assoc 200:1678–1681, 1992. Millichamp NJ: Conjunctiva. In Auer JA, Stick JA, editors: Equine Surgery, ed 2, Philadelphia, 1999, WB Saunders, pp 465–471.

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Mosunic CB, Moore PA, Carmicheal KP, et al: Effects of treatment with and without adjuvant radiation therapy on recurrence of ocular and adnexal squamous cell carcinoma in horses: 157 cases (1985–2002), J Am Vet Med Assoc 225:1733–1738, 2004. The´on AP, Pascoe JR, Carlson GP, Krag DN: Intratumoral chemotherapy with cisplatin in oily emulsion in horses, J Am Vet Med Assoc 202:261–267, 1993. The´on AP, Pascoe JR, Meagher DM: Perioperative intratumoral administration

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of cisplatin for treatment of cutaneous tumors in equidae, J Am Vet Med Assoc 205:1170–1176, 1994. The´on AP, Pascoe JR, Madigan JE, Carlson G, Metzger L: Comparison of intratumoral administration of cisplatin versus bleomycin for treatment of periocular squamous cell carcinomas in horses, Am J Vet Res 58:431–436, 1997. Townsend WM: Food and fiber–producing animal ophthalmology. In Gelatt KN,

editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 1275–1335. Wilkie DA, Burt JK: Combined treatment of ocular squamous cell carcinoma in a horse, using radiofrequency hyperthermia and interstitial 198Au implants, J Am Vet Med Assoc 196:1831–1833, 1990. Witt RP: Treating ocular carcinoma in cattle, Vet Med Small Anim Clin 79:1087–1089, 1984.

CHAPTER

8

Surgery of the cornea and sclera Kirk N. Gelatt1 and Dennis E. Brooks2 1

Small animals; 2Large animals and special species

Chapter contents Introduction

191

Surgery for corneal lacerations

210

Surgical anatomy

192

Surgery for corneal foreign bodies

214

Surgical pathophysiology

193

Corneal adhesives

215

Preoperative treatment considerations

194

Corneal grafts/keratoplasty

216

Surgical instrumentation for corneal and scleral surgeries

195

Thermokeratoplasty

228

Surgical procedures for superficial corneal diseases

196

Surgical treatment of limbal and scleral diseases

229

Surgical procedures for deep corneal ulcerations

201

Adaptations for large animals and special species

232

Introduction Corneal diseases occur frequently in the dog and cat. In the dog, corneal diseases may be primary or secondary to other ophthalmic diseases. Secondary corneal diseases occur frequently in the brachycephalic breeds and with keratoconjunctivitis sicca. In dogs, the common causes of corneal diseases are trauma, inflammations and ulcerations, degenerations, and dystrophies. Congenital abnormalities and neoplasia of the canine cornea are infrequent. In cats, corneal diseases are common, and are usually associated with inflammations, trauma, and sequestration (corneal black spot, corneal mummification). In both cats and dogs, trauma of the cornea occurs most frequently in animals under 1 or 2 years of age. Corneal diseases cause varying degrees of opacification. Invasion of blood vessels, pigment cells, neoplastic cells, lipid material, and leukocytes from the limbus reduce corneal transparency. Edema results from local corneal inflammation or impaired corneal endothelia that can no longer remove fluids from the cornea. With reduction in corneal transparency, vision can be gradually impaired; with total corneal opacification, vision can be lost temporarily or permanently. Treatment of corneal diseases in dogs and cats is quite successful using medical, surgical, and a combination of these therapies. Corneal diseases are often noticed early by the pet’s owner because of the onset of pain, blepharospasm, photophobia, conjunctival hyperemia and chemosis, tearing, and rubbing of the eyelids. As a result, the possibility of successful

treatment is higher. Medical treatment of corneal diseases usually involves the direct instillation of drugs on the affected tissue. Topical drugs include solutions, suspensions, and/or ointments. When corneal diseases are progressing or are unusually severe, the topical route may be supplemented with drugs provided systemically and subconjunctivally. Corneal penetration by most antibiotics is limited by the lipophilic corneal epithelium. Chloramphenicol is still the antibiotic of choice when the epithelium is intact, and therapeutic levels of antibiotic are necessary in the cornea and anterior chamber. With corneal ulceration, the epithelial barrier is markedly reduced, and the administration of broad-spectrum topical antibiotics is recommended. The most frequently used topical antibiotics include gentamicin, chloramphenicol, tobramycin, the fluoroquinolones and the combination of neomycin, polymyxin B, and bacitracin. In corneal diseases with vascularization of the cornea and/or secondary iridocyclitis, systemic antibiotics are often indicated and are highly successful. Surgical treatment of corneal diseases in the dog and cat is often the primary modality. The normal cornea, exposed suddenly to trauma or ulceration, often requires several days to initiate satisfactory inflammatory and healing responses. In the meantime, the infectious agents, proteases, and collagenases (from bacteria and damaged corneal cells) can cause rapid degradation of the cornea, and threaten the integrity of the cornea and maintenance of vision. Surgical treatment can jump-start the healing process and markedly reduce the length of the lag phase for healing, as well as provide vital structural corneal support. Corneal surgery

8

Surgery of the cornea and sclera

includes partial keratectomy (or removal for treatment or biopsy), keratotomies (single or multiple incisions), transposition (movement from one site to another), primary closure for small corneal ulcers and lacerations, and transplantation (autogenous and homologous) or grafting of corneal tissues to replace cornea lost to disease.

Surgical anatomy Dog and cat corneal anatomy Dog and cat corneas are relatively large compared to those of humans, probably to assist in night vision. Animals with large corneas are typically nocturnal, as large corneas allow greater amounts of light to enter the pupil during reduced illumination. Most animal corneas are roughly elliptical in shape with the vertical diameter slightly less than the horizontal diameter. The normal dog cornea measures 12–16 mm vertically and 13–17 mm horizontally, and is 0.45–0.55 mm thick centrally and 0.50–0.65 mm thick peripherally. The normal cat cornea measures 15– 16 mm vertically and 16–17 mm horizontally, and is about 0.58 mm thick centrally and peripherally. Corneal measurements, both diameters and thicknesses, have not been established for different ages and the different breeds in either the dog or cat. The cornea, along with the sclera, forms the fibrous tunic of the globe (Fig. 8.1). The zone where the cornea gradually

Central (axial) cornea Pupil

becomes opaque and changes to sclera is the limbus. The limbus is sufficiently forward of the aqueous humor filtration angle or the iridociliary cleft (or ciliary cleft) to prevent direct visualization of the aqueous outflow pathways. Dog and cat corneas are divided into axial (central) and peripheral, with the central area most important for vision. Often the cornea is divided into quadrants. The central cornea is generally the thinnest and most often affected with ulcerations. Dog and cat corneas have four different microscopic regions. From external to internal, these subdivisions include: 1) epithelia with basal membrane; 2) thick stromal layer; 3) Descemet’s membrane; and 4) the posterior single layer endothelia. A modified anterior region of the corneal stroma, Bowman’s membrane, is absent in the dog and cat, but present in humans and most birds. The epithelial layer is normally about 5–7 cells thick and consists of: 1) outer two to three layers of non-keratinized squamous cells; 2) middle two to three layers of polyhedral or wing cells; and 3) a single layer of basal columnar cells that are positioned on a basement membrane (Fig. 8.2). The apparent turnover of corneal basal epithelia is about 7 days. The basement membrane, produced by the basal corneal epithelia, attaches the basal epithelial cells via hemidesmosomes to the anterior stroma. Defects in the canine basal corneal epithelia and basement membrane are thought to contribute directly to the development of recurrent corneal erosions. The corneal stroma, or substantia propria, accounts for about 90% of the corneal thickness, and consists of parallel

Peripheral (para-axial) cornea

Anterior chamber

Limbus

Anterior chamber angle

Sclera

Posterior chamber Lens Iris Zonules A

Ciliary body (pars plicata)

B

Fig. 8.1 The surgical and microanatomy of the dog and cat cornea. (a) The anatomic relationships of the cornea to the other tissues in the anterior segment of the eye. (b) The microscopic layers of the dog and cat cornea include: (A) epithelium; (B) stroma; (C) Descemet’s membrane; and (D) the endothelium. H & E, 25
.

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Surgical pathophysiology

(mean), respectively. Corneal endothelial count varies by age, and a count of 3216 cells/mm2 has been reported in the horse.

Bovine corneal anatomy The oval cornea of the adult cow is roughly pear-shaped and measures 22–24 mm vertically and 27–32 mm horizontally. Its thickness also varies with the center thicker (range from center and periphery: 0.75 to 0.85 mm). The radius of curvature for the bovine cornea varies from 14.7 mm (vertically) and 16.8 mm (horizontally).

Surgical pathophysiology Fig. 8.2 The epithelial layer is usually five to seven cells thick. The basal epithelia are secured to the anterior stroma by a basement membrane. H & E, 100
.

bundles of collagen fibrils, few fibrocytes (also called keratocytes), and a matrix of glycosaminoglycans. The arrangement of these fibrils and the matrix of glycosaminoglycans become distorted with disease and is the basis of corneal opacification. Corneal sensory nerves, distributed from the mid posterior stroma from the ophthalmic branch of the trigeminal nerve, eventually terminate in subepithelial plexuses to provide free nerve endings in the epithelial wing cell layer. As a result, superficial corneal ulcers are usually more painful in dogs than ulcerations involving the deep corneal stroma. Corneal sensitivity may be reduced in the brachycephalic breeds, possibly predisposing the cornea to damage. Descemet’s membrane is the basement membrane produced by the posterior cells, the endothelia. Descemet’s membrane, a relatively thick basement membrane that increases in thickness with aging, is clear and somewhat elastic. Surgical repair is necessary to prevent imminent corneal rupture when exposed Descemet’s membrane or a descemetocele is clinically visible. The single layer of endothelia forms the posterior layer of the cornea, and consists of hexagonal-shaped cells that interdigitate with each other laterally with different cell junctions, including zonulae occludentes, maculae adherentes, and nexi. These metabolically active cells are the principal site for removal of water from the cornea via an NaþKþ ATPase ‘pump’. Surgical and traumatic damage, as well as aging and decreased numbers of endothelia, alter this state of ‘deturgescence’, and edema of the cornea may result.

Equine corneal anatomy The oval adult equine cornea measures 26–28 mm vertically and 32–38 mm horizontally, with a radius of curvature of about 17 mm. The thickness also varies, with the center measuring as thin as 0.56 mm and the periphery 0.8 mm. Corneal thickness measurements can vary by the in-vivo or in-vitro method used (direct measurement in fixed tissue), ultrasonography or ultrasound pachymetry and specular microscopy. Ultrasonic pachymetry of the central equine cornea reveals 785  2.98 mm to 858 mm (mean). Dorsal and lateral measurements are 932.5 mm (mean) and 879.5 mm

Diseases alter corneal transparency. Invasion of the cornea with blood vessels from the limbus and bulbar conjunctiva; accumulation of extracellular and intracellular fluids and edema; infiltration with the different types of leukocyte; migration of pigment cells from the limbus, conjunctiva, and anterior synechiae; and deposition of lipid, cholesterol, and calcium products all reduce the cornea’s ability to transmit images. Fortunately, dog and cat corneas have considerable capacity for repair and the reestablishment of transparency. Corneal nutrition is from three sources: precorneal/preocular film, limbal vasculature, and the aqueous humor posteriorly. The corneal epithelia respond quickly to damage by undergoing mitosis and sliding of new wing cells into the corneal defect. The entire cornea can be re-epithelialized in 7–10 days, although firm adhesion of the new epithelia by hemidesmosomes requires several weeks. New corneal epithelium is usually semipermeable to topical fluorescein, staining a faint green. During the corneal ulcerative process, proteases, collagenases, and other enzymes are released from degenerating corneal cells, leukocytes, and certain bacteria. These enzymes degrade the collagen fibrils and glycosaminoglycans, potentiating the ulcer’s progression even in the absence of sepsis. Superficial corneal ulcers are often more painful than deeper ulcerations. Both the corneal epithelium and anterior corneal stroma possess pain and pressure receptors that are part of the long ciliary nerves that arise from the ophthalmic branch of the trigeminal (fifth) nerve. Not only does pain occur from stimulation of these nerve endings, but also an axonal reflex that results in a secondary iridocyclitis (reflex miosis, conjunctival and anterior uveal hyperemia), and altered blood–aqueous barrier (aqueous flare). Hence, corneal ulceration commonly causes secondary iridocyclitis, which requires treatment concurrent with the corneal ulcer therapy. As the corneal ulcer is being rapidly covered by healing epithelia, the corneal stroma has a slower and longer repair phase. Often the stroma is invaded by blood vessels from the limbus and bulbar conjunctiva, as well as leukocytes from tears, blood vessels, and limbus. Fibroblasts, converted from keratocytes and histiocytes, slowly produce new collagen fibrils and local glycosaminoglycans matrix. This process takes several weeks to a few months. Following deep keratectomy, complete recovery of corneal stroma to normal thickness may take months, and the stroma may not totally

193

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return to normal thickness. It has been suggested that the limit of three superficial keratectomies for the dog appears related to failure of total stromal regeneration. After superficial keratectomy, the new collagen fibrils may not perfectly realign with adjacent normal corneal lamellae, resulting in variable amounts of scarring. Fortunately, scarring after superficial keratectomies in the dog and cat is limited. In fact, if one ranks the tendency for corneal scarring among animals, it appears that the cat and cow have the least tendency, the dog ranks in the middle, and the horse has the greatest tendency for corneal scarring after disease or surgery. Resolution of the corneal blood vessels after stromal repair requires several weeks, often resulting in ghost vessels that can be observed years later by biomicroscopy. Chronic corneal irritation in animals usually results in invasion of the cornea with melanocytes from limbus and bulbar conjunctiva, epithelial cells, and histiocytes. This intracellular melanin pigment, observed clinically as brown-to-black areas in the cornea, appears histologically in the corneal basal and wing cell layers, and in anterior corneal stroma. Once the canine cornea becomes pigmented, the opacification from this pigmentation is difficult to eliminate medically or excise surgically, but can usually be controlled sufficiently to allow clinical vision. Repair of defects in Descemet’s membrane depend on the formation of new basement membrane by corneal endothelium and requires several weeks. Posterior endothelial regeneration is influenced by animal species and age: in young animals the defect is covered by new corneal endothelia derived primarily by mitosis; in older animals these defects are covered primarily by endothelial cell enlargement by adjacent cells. In older animals, it appears that Descemet’s membrane progressively thickens. Once Descemet’s membrane is cut, the membrane curls and retracts. The exposed posterior stroma is rapidly covered with a fibrin clot. Adjacent endothelial cells, by either mitosis or enlargement, cover the fibrin clot, and over several weeks produce a new Descemet’s membrane. The rabbit corneal endothelia seem to rapidly undergo mitosis and slide to cover areas on Descemet’s membrane or posterior stroma within days. Regeneration of endothelia in the dog and cat is poorly understood. Like children, the puppy and kitten corneal endothelia demonstrate remarkable and rapid regeneration by mitosis. However, the density of corneal endothelia in the dog gradually declines with age, suggesting that regeneration is not occurring. The occurrence of persistent corneal edema and primary endothelial dystrophies in dogs indicate that regeneration of corneal endothelial cells in older animals does not occur. The normal cornea also becomes slightly thicker in older dogs, presumably from less effective corneal dehydration associated with decreased numbers of corneal endothelia. The density of corneal endothelial cells in the dog, critical to maintain a cornea devoid of edema, ranges from 1200 to 1500 cells mm2, with 2500–3000 cells mm2 being normal. In corneal tissue banks for humans, at least 2000 cells mm2 is considerable essential for corneal donor tissue for corneal transplantation. Because of limited numbers of endothelial cells in older dogs, corneal edema is more apt to occur after cataract surgery. Cataract surgery in dogs generally results in the loss of 10–20% of the corneal endothelia. Hence, in very

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old dogs having cataract surgery, damage to the corneal endothelium during phacoemulsification must be considered seriously, and more postoperative corneal edema is expected.

Preoperative treatment considerations The preoperative treatment of corneal diseases in animals depends on the condition. With limbal and corneal neoplasms, dermoids, focal corneal lipidosis, and corneal cysts, treatment of the cornea prior to surgery is not usually necessary. In contrast, corneal inflammations, foreign bodies, ulcerations, and partial and full-thickness lacerations may require adequate preoperative treatment to ensure the success of the surgical procedure, especially if entry into the anterior chamber is likely. With corneal defects, i.e., ulcerations, descemetoceles, corneal ulcerations with iris prolapse, corneal foreign bodies, and partial-to-full-thickness lacerations, topical and systemic antibiotics are indicated to prevent the infectious process from spreading intraocularly.

Dog and cat Topical antibiotics most frequently include chloramphenicol, gentamicin, tobramycin, and the combination of neomycin, polymyxin B, and bacitracin. Most often the bacteria recovered from corneal ulcers by culture are Staphylococcus and Streptococcus spp., which are sensitive to most antibiotics. Systemic antibiotics, such as amoxicillin or cephalexin, are administered when corneal disease is advanced and integrity of the globe threatened. With inflammatory corneal diseases, secondary involvement of the anterior uvea is common. Miosis, flare in the anterior chamber, fibrin formation, lowered intraocular pressure, photophobia, and swelling of the iris and ciliary body usually accompany corneal ulcerations and lacerations. Instillations of iridocycloplegics, such as 1% atropine or 0.3% scopolamine with 10% phenylephrine, are indicated to reduce ocular pain, decrease the likelihood of posterior synechiae and cataract formation, and retract the iris from full-thickness axial corneal wounds. The physical objective of mydriatic treatment is to moderately dilate the pupil, but still permit some iris movement that discourages the formation of posterior synechiae. The strong iridocycloplegics, such as 1–3% atropine, are long acting and can markedly decrease aqueous tear production. An acutely dry cornea does not heal readily! As the pupil size can be ascertained daily through most corneas, the intensity and concentration of mydriatic(s) can be adjusted quickly to maximize therapeutic effects and minimize side effects. Corneal ulcers in the dog occasionally progress even though sepsis is not demonstrable. This expansion of the edges of the corneal ulcer may result from the local release of proteases, collagenases, and other enzymes liberated by dying corneal and inflammatory cells. Specific treatment to combat this effect may be achieved by topical 5.0% acetylcysteine or preferably autogenous serum. Non-steroidal anti-inflammatory drugs (NSAIDs) such as flunixin meglumine (0.5 mg/kg IV; BanamineW, ScheringPlough, Kenilworth, NJ) or carprofen (2 mg/kg PO; RimadylW, Pfizer Animal Health, Exton, PA) are used in the

Surgical instrumentation for corneal and scleral surgeries

dog to reduce postoperative iridocyclitis, pain, and conjunctival and eyelid swelling. These drugs may mimic the effects of steroids on the eye but with few side effects; however, like corticosteroids, they appear to delay corneal vascularization. The dog and cat eyes rotate during gas anesthesia ventromedially, and collapse once the anterior chamber has been opened. The use of non-depolarizing neuromuscular blocking agents such as atracurium (0.2 mg/kg IV; GlaxoWellcome Research, Triangle Park, NC) paralyzes the animal, including the extraocular muscles. As a result, the eye position remains normal and the lack of extraocular muscle tone reduces intraocular tissue displacement once the anterior chamber is entered. Because of the paralysis of all striated musculature, including the muscles associated with breathing, artificial ventilation in these anesthetized patients is essential until the drug-induced paralysis ceases or is reversed (see Chapter 3). With general anesthesia, loss of tear production, and lack of the protective blink reflex, the cornea quickly dries. During surgery, the corneal surface should be intermittently irrigated with lactated Ringer’s solution or balanced saline solution.

Horse Preoperative treatment is not uncommon in horses, and often directed at the primary corneal disease. Although the most common topical antibiotics for the horse include the triple antibiotics (neomycin, bacitracin, and polymyxin) and gentamicin or tobramycin, ciprofloxacin may have the greatest activity and least number of resistant organisms. Topical gentamicin, perhaps because of its high frequency of use as the first-line topical antibiotic for nearly four decades, has been reported to now encounter the highest number of resistant Pseudomonas and Streptococcus organisms. As a result, intensive or progressive corneal ulcers in the horse should be cultured, if possible, to help guide antibiotic therapy. Mydriasis is often indicated for horses with corneal diseases to reduce the ocular pain, dilate the pupil, and stabilize the blood–aqueous barrier. Of the species requiring mydriatics, the horse appears the most sensitive to the systemic effects of atropinization. Hence, mydriatics are administered to effect (a maximally dilated pupil) for a day or two, and then reduced to maintain the dilated pupil to minimum levels. Close daily observation of the horse for intestinal motility and output of feces is important. Any decrease in intestinal motility or apparent abdominal distress should initiate immediate reduction or cessation of topical anticholinergic mydriatic therapy. Antifungal medications are important in the horse because of the not-infrequent fungal involvement in corneal disease in many areas of the world. Natamycin, also known as pimaricin, (5%) is the only commercially available antifungal agent in the United States; its reported activity is for Fusarium and some Aspergillus species. Other antifungals must be individually prepared and include miconazole (1%), fluconazole (0.2%), voriconazole (1%), itraconazole (1%), and amphotericin (0.15%). These topical antifungals are often administered for several weeks. The search for effective systemic antifungals continues! The horse eye is characterized by a profound inflammatory response which often must be medically controlled in

order to treat the infectious agents, but prevent excessive inflammation which can cause anterior and posterior synechiae formation, secondary cataracts, and phthisis bulbi (destruction of the ciliary body with markedly reduced aqueous formation rates, intraocular pressure less than 5 mmHg, cataract formation, and retinal detachment). Topical and systemic corticosteroids must be administered carefully in the horse, as potential adverse effects are not infrequent. Topical and especially systemic non-steroidals, such as flunixin meglumine (1 mg/kg PO, IV, or IM q12h) are effective in controlling secondary uveitis, reducing uveal exudation, and relieving ocular discomfort. For horses with severe corneal disease, the subpalpebral medication system to administer medications to the eye is most useful when the medications are delivered to the eye six to eight times daily for many weeks.

Cattle Generally economics preclude preoperative treatments in cattle. However, for highly valuable cattle, therapy similar to the horse can be used. Systemic antibiotics and other drugs are often different between horses and cattle, and drug residues in milk and meat may be important in cattle.

Surgical instrumentation for corneal and scleral surgeries Small animals The investment in surgical instruments depends on the expertise of the veterinary surgeon and the anticipated patient load with corneal surgical diseases (see Table 1.4, p. 12). Magnification is essential for corneal surgeries. Head loupes can provide magnification at levels of 2.5 to 4
; the operating microscope provides at least 10
and is generally preferred. With considerable corneal surgery and keratoplasty, the operating microscope is recommended. Either standard or microsurgical instruments may be used, or a combination of both sizes. Minimal instruments include the following.

•

•

•

For exposure of the cornea and a possible lateral canthotomy: tenotomy or Steven’s scissors, eyelid speculum, tissue forceps (Bishop–Harmon), and needle holder (standard; with lock: Castroviejo). For additional information on lateral canthotomy, see Chapter 2. For corneal tissues: Colibri and tying forceps (with 1
2 teeth), Beaver scalpel handle and blades (Nos 6400, 6500, and keratome), corneal scissors (right and left handed), iris scissors, disposable electrocautery, Martinez corneal dissector, associated cannulas, needle holder (microsurgical size and without lock), and a set of corneal trephines (at 0.5 mm increments). The diamond knife is very useful for corneal surgery and can provide exact control of the depth of the corneal incision in increments of 0.2, 0.3, 0.4, 0.5, 0.6 and 0.8 mm. For keratoplasty, additional instruments include corneal cutting block (often TeflonW) and punch. At least one or two different sizes of Flieringa rings are useful for corneal transplantation, and are temporarily sutured to the bulbar conjunctiva and episclera to prevent collapse of the globe (see Chapter 1).

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Both absorbable and non-absorbable 6-0 to 10-0 sutures are used for corneal surgeries. The least reactive suture is the non-absorbable nylon, and is essential for keratoplasty, but removal of the sutures is usually necessary. Absorbable sutures, such as polyglactin 910 or polyglyconate, are the usual choices with either reverse cutting or spatula needles. Suture techniques include simple interrupted, simple continuous, double saw-tooth, and others. Ideally a corneal stitch should be 75–90% of the corneal thickness with ‘bites’ about 2 mm of tissue for maximum tissue holding (especially with edematous corneal tissue).

Large animals The ophthalmic surgical instrumentation for performing corneal or corneoscleral surgeries in large animals is identical to that for small animals. For these surgeries using limited magnification, standard size instruments are most useful; if the operating microscope is used as well as general anesthesia, microsurgery ophthalmic instruments are often employed.

Surgical procedures for superficial corneal diseases Superficial corneal diseases are usually confined to corneal epithelia and anterior stroma, and may be treated surgically. For instance, corneal dermoids generally extend into the anterior stroma and may involve adjacent bulbar conjunctiva (Fig. 8.3). Treatment is superficial keratectomy. Corneal lipidosis often affects the anterior corneal stroma, and may be removed by superficial keratectomy. Recurrent corneal erosions in the dog appear related to corneal epithelial dystrophy and defects in the basement membrane which result in defective adhesion during healing of these superficial erosions and frequent recurrences (Fig. 8.4). Several surgical procedures, including superficial keratectomy, have been used to treat this condition. The superficial keratectomy procedure may be used for corneal sequestra in cats limited to the anterior corneal stroma.

Fig. 8.3 Corneal dermoid in a St Bernard puppy. Covered with long coarse hair, that is highly irritating, the congenital mass involves the lateral cornea, limbus, and bulbar conjunctiva. Recommended treatment is superficial keratectomy.

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Fig. 8.4 Recurrent corneal erosion in a 5-year-old Boxer dog. The raised epithelial rim or lip, which stains with rose Bengal, surrounds the erosion (also stains with fluorescein).

In this section, surgical techniques that involve corneal epithelium and anterior aspects of the corneal stroma are presented and include: 1) superficial keratectomy (partial and complete); 2) superficial punctate, grid or linear keratotomy; and 3) corneal biopsy.

Superficial keratectomy (partial and complete) Keratectomy may prove useful in the early stages of ulcerative keratitis when infection is confined to the corneal epithelium and anterior third or half of the cornea stroma, and in later stages of stromal keratitis when the epithelium has healed. Removing necrotic tissue by keratectomy speeds healing, minimizes scarring, and decreases the stimulus for keratitis and iridocyclitis. In superficial keratectomy the corneal epithelia and variable amounts of anterior stroma are excised. The procedure may involve the entire cornea or only part of the cornea. The thickness of stroma removed depends on the corneal disease. When the superficial keratectomy is limited to the outer one-third of the cornea, the postoperative wound is treated medically as a corneal ulcer. However, when the partial superficial keratectomy extends for more than one-half to two-thirds of the corneal stroma, the defect is covered with a conjunctival graft. While regeneration of corneal epithelia appears complete after superficial keratectomy, total recovery of the corneal stromal thickness is questionable. A single cornea subjected to three superficial keratectomies appears to have a stroma of about one-half to two-thirds normal thickness thereafter. Indications for superficial keratectomies include corneal dermoid, chronic superficial keratitis (pannus), pigmentary keratitis, chronic and recurrent corneal erosions, corneal and/or limbal neoplasia, ulcerative keratitis with sequestration in cats (Fig. 8.5), corneal superficial dystrophies (usually lipidosis and calcification), and superficial corneal foreign bodies. In some of these diseases, the cause(s) has not been determined, and although the involved corneal tissue(s) appears completely excised, recurrence may occur. For some of these conditions, such as pigmentary keratitis, the superficial keratectomy may re-establish a clear cornea, but if the predisposing factors, such as lagophthalmia, nasal fold trichiasis, or tear film disorder, are not resolved, the cornea will become pigmented again.

Surgical procedures for superficial corneal diseases

A

B

Fig. 8.5 Corneal sequestration in cats consists of a distinct central brown-to-black area of necrotic stroma. (a) Corneal vascularization and inflammation may surround the lesion. (b) Immediate postoperative appearance after superficial keratectomy. If the keratectomy is limited to less than one-third of the corneal stroma, it is treated as a corneal ulcer. A bulbar conjunctival graft may also be used to cover the surgical defect, and may decrease the possibility for recurrence of sequestrum.

There are several different modifications of the superficial keratectomy procedure. As a rule, only the diseased area within epithelial and anterior stromal layers is excised. While the normal dog and cat corneas are about 0.5–0.6 mm thick, the abnormal cornea may exceed 1.0 mm in thickness. When the entire cornea is diseased, superficial keratectomy may be performed using a limited-depth corneal trephine or diamond knife, or by dividing the cornea into four quadrants (much like cutting a pie or cake) and separating the opaque superficial layers of cornea from the deeper clear corneal stroma. Instruments used to perform the superficial keratectomy include: eyelid speculum, smooth and 1
2 teeth tissue forceps (Bishop–Harmon or Colibri), Beaver scalpel handle and No. 6400 microsurgical blade or diamond knife, strabismus or tenotomy scissors, irrigator bulb, and small cannula. Additional instruments to perform the lateral canthotomy may be necessary when improved exposure of the corneal site is necessary. Other corneal instruments that can assist in the superficial keratectomy are the Martinez dissector, a corneal trephine whose depth can be preset to 0.2–0.3 mm, and the diamond knife with a micrometer (which limits the depth of the corneal incision). This procedure is generally performed under general anesthesia. Superficial keratectomy is usually limited (partial) to the diseased cornea. The periphery of the diseased area is encircled with an incision using the Beaver scalpel handle and No. 6400 microsurgical blade, or the diamond knife with the micrometer set at 0.15 or 0.25 mm, or a preset corneal trephine (0.15–0.25 mm). The incision should be of sufficient depth to remove the base of the diseased cornea, as estimated preoperatively by slit-lamp biomicroscopy (Fig. 8.6a). Often, the cornea is vascularized, and limited hemorrhage occurs during the incision. To prevent hemorrhage from obscuring the incision, a continuous stream of 0.9% sterile saline is directed at the leading aspects of the corneal incision as it is performed. This hemorrhage will usually cease once sufficient time has elapsed to permit clotting. If a conjunctival graft is applied to the keratectomy site, the surgical defect may be constructed as a square lesion. Once the corneal lesion has been outlined, the edge of the superficial keratectomy section is grasped carefully

with 1
2 teeth tissue forceps to permit separation of the diseased cornea from the underlying stroma (Fig. 8.6b). The dissection plane within the stroma should remain in the same parallel lamellae throughout the superficial keratectomy. If the Beaver knife is used, the instrument must be held tangential to the corneal stroma to prevent progressive deeper dissection into the stroma (Fig. 8.6c). Alternately, the Martinez dissector facilitates this dissection to remain within the respective corneal lamellae (Fig. 8.6d). Once the diseased cornea has been completely separated from the stroma, it is lifted from the surgical wound (Fig. 8.6e). If some tags of stroma remain, they are carefully cut with utility or tenotomy scissors. If additional areas of diseased cornea are still present, the procedure may be repeated in these areas. Partial superficial keratectomies are generally limited to the outer one-half of the cornea unless a conjunctival graft, corneoconjunctival graft, or lamellar corneal graft is attached afterwards to the surgical wound. Postoperatively, the superficial keratectomy wound is not usually covered with a nictitating membrane flap or complete temporary tarsorrhaphy. Topical broad-spectrum antibiotics are instilled four to six times daily. Topical 1% atropine is instilled to maintain a moderate to completely dilated pupil (one drop daily or every other day). Topical atropine can reduce aqueous tear formation, as measured by the Schirmer tear test, by 50–75%. A marked decrease in tears can prolong corneal reepithelialization by several days. Every day or every 2 days the re-epithelialization of the superficial keratectomy wound is evaluated with and without topical fluorescein. Re-epithelialization usually starts within 48 h. The entire canine cornea can re-epithelialize within 7–10 days. New epithelia are somewhat translucent, stain faintly with topical fluorescein, and adhere incompletely. Each day the area of fluorescein retention (devoid of corneal epithelia) should become smaller, as reepithelialization occurs 360 . If re-epithelialization is slow or ceases, topical aqueous 0.5% povidone–iodine solution is carefully applied to the wound edges to stimulate epithelial activity.

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A

B

D

E

C

Fig. 8.6 In the superficial keratectomy procedure, a section of corneal epithelium and the superficial stroma are excised. (a) The periphery of the corneal dermoid is incised with the Beaver No. 6400 microsurgical blade to a depth of about 0.2–0.3 mm. (b) The edge of the lesion is grasped and lifted with a 1
2 teeth thumb forceps, and separation of the lesion from the underlying clear stroma is continued by scalpel dissection. (c) During the dissection of the stroma, the microsurgical blade is held tangential to avoid entry into the deeper stromal lamellae. (d) The Martinez corneal dissector or separator may also be used (instead of the microsurgical blade) during this part of the surgery for lamellar dissection. (e) Once the stromal dissection has been completed, the lesion is carefully removed, resulting in a corneal defect.

Corneal healing after superficial keratectomy for the treatment of feline corneal sequestration is often slower than normal and more scarring results. Once re-epithelialization of the superficial keratectomy site is complete, topical antibiotics are continued for few days. Final corneal clarity may require several weeks during which the corneal stroma becomes reorganized. Topical corticosteroids, such as 0.25– 0.5% prednisolone or 2.5% hydrocortisone, may be administered two to four times daily, or cyclosporine administered once daily may be used to minimize corneal scarring, but are not usually necessary. Although some corneal scarring may result after the superficial keratectomy procedure, the opacity is not usually dense in the dog and cat. Postoperative complications after superficial keratectomies are infrequent. Bacterial infection of the surgical wound is rare, provided appropriate topical antibiotics are administered. Postoperative reduction in tear production will delay corneal healing, and increase the possibility of corneal vascularization and more scarring. After superficial keratectomies in brachycephalic breeds, the cornea should be evaluated daily or every other day. Lagophthalmos, infrequent blinking, central corneal exposure, and marginal tear production are often associated with corneal diseases in these breeds, and can prolong corneal re-epithelialization of the superficial keratectomy site excessively. Postoperative corneal scarring may be more in dogs than in cats. Use of only superficial keratectomies to treat pigmentary keratitis in dogs is not successful. The surgical areas often re-pigment within months. For the superficial keratectomy to have reasonable success for canine pigmentary keratitis, additional medical and/or surgical treatments are indicated, such as permanent medial or lateral canthoplasty, removal of nasal fold trichiasis, and medically increasing tear production using topical cyclosporine or oral pilocarpine.

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These treatment modalities address the basic problems that contributed to the development of the original corneal pigmentation. Superficial keratectomy for the clinical management of canine chronic superficial keratitis (pannus) is not curative, but can remove the dense corneal pigmentation in advanced disease and immediately restore vision in these dogs. However, the healing periods after superficial keratectomies for the treatment of this disease are not predictable. Recurrence of pannus and corneal vascularization may occur before or concurrent with the corneal re-epithelialization, and necessitate topical corticosteroids or cyclosporine before re-epithelialization is complete. Beta radiation may be indicated to retard corneal vascularization during immediate postoperative healing in selected patients. Long-term control of pannus still depends on daily instillations of corticosteroids and/or cyclosporine, adjusted for the severity of the disease. Overall results with superficial keratectomies are very good. Recurrence of the original corneal disease may again opacify the cornea, but the procedure provides a temporarily clear cornea. Removal of corneal scar tissue, corneal dermoids, embedded corneal foreign bodies, and other corneal opacities with superficial keratectomies is usually curative.

Adaptations in large animals and special species Keratectomy may be indicated in cases of melting ulcers in horses. Keratectomy is thought to speed healing by removing necrotic and infected tissue, and encouraging vascularization, minimizing scarring, and decreasing the stimulus for anterior uveitis. Necrotic tissues that are often present in case of melting ulcers should be removed and this can be achieved with a cellulose sponge or a fine-toothed

Surgical procedures for superficial corneal diseases

A

B

Fig. 8.7 Treatment of corneal scarring by superficial keratectomy and amnion graft in a horse. (a) A granulomatous scar is present at the surgical site 2 years postoperatively for superficial keratectomy and permanent conjunctival graft for corneal squamous cell carcinoma. (b) A slight scar is present at the surgical site five months postoperatively.

forceps (e.g., 0.12 mm Colibri forceps). Additionally, careful debridement can be done with microsurgical corneal scissors, a microsurgical blade or a corneal dissector. A corneal incision to outline the lesion to be removed can be done with a corneal trephine, a diamond knife or a microsurgical blade (e.g., Beaver No. 6400 microsurgical blade). The depth of the incision in the stroma should be adequate to remove the lesion completely. Once the initial incision is made, the edge of the tissue to be removed is grasped by a forceps (e.g., 0.12 mm Colibri forceps), and a corneal dissector (e.g., Martinez corneal dissector) is introduced and held parallel to the cornea. The dissector is used tangentially to separate the corneal lamella without penetrating deeper than the original cutting plane. The cornea is then separated until the opposite incision line is reached. Depending on the stromal defect, a conjunctival graft may be placed subsequently. Superficial keratectomy is also performed during any grafting procedure to prepare the bed for conjunctival, amniotic membrane or corneal graft. The complications of superficial keratectomy are minimal, but include slow healing, infection, granulation tissue formation, perforation, and excessive scar formation. Superficial keratectomy may also be used in the treatment of superficial corneal scarring, with postoperative treatment of the corneal healing response (Fig. 8.7).

Superficial punctate, grid, and linear keratotomies Superficial punctate, grid, and linear keratotomies are relatively new surgical procedures used to treat chronic corneal erosions and refractory corneal ulcers in dogs and other species (Fig. 8.8). Investigations into corneal recurrent erosions (indolent ulcer or Boxer ulcer) in the dog indicate defective basal corneal epithelia and basement membrane. Defects in the basement membrane, including paucity of hemidesmosomes and multiple layers of basement membrane, appear

Fig. 8.8 Corneal erosions, stained with topical fluorescein, are characterized by slow healing and recurrence. New surgical procedures, such as the superficial punctate and grid keratotomies, attempt to enhance healing and prevent recurrences by expanding the adhesion of the epithelia and basement membrane to the anterior stroma.

to contribute directly to the onset of these highly painful but shallow corneal ulcers, and to their variable but often prolonged healing. Both surgical procedures attempt to improve adhesion of the defective epithelia and basement membrane to the anterior stroma by making multiple shallow grooves in the epithelia and anterior stroma that provide deeper attachment sites. As a result, basal corneal epithelia increase their surface contact and adhesion through these incomplete needle or linear tracks to the anterior stroma. As the entire cornea is involved, these procedures are used for most of the entire cornea including the actual erosion site. Punctate keratotomy leaves smaller scars than grid keratotomy. The keratotomy procedures are usually preceded by debridement using a cotton swab and topical anesthesia of the edges of these chronic erosions for 1 or 2 weeks. If epithelialization has not occurred in 12–14 days, one of these

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keratotomies is performed. Partial-to-complete superficial keratectomy has also been used for this condition. Other surgical procedures for recurrent and slow healing corneal erosions, such as transplantation of small lenticules of new and healthy epithelium (keratoepithelioplasty), microdiathermy of Bowman’s membrane, and neodymium:yttrium aluminum garnet (Nd:YAG) laser photo-induced adhesion of corneal epithelia, have not been reported in the dog.

Superficial punctate keratotomy Superficial punctate keratotomy may be performed in quiet dogs with only topical anesthesia, or with some sedation in less cooperative dogs. The grid procedure may be performed under local anesthesia, but general anesthesia is recommended if most of the cornea is involved. Prior to both procedures, loose corneal epithelia surrounding the chronic erosion are debrided with thumb forceps or sterile cotton swabs. In superficial punctate keratotomy, multiple anterior stromal punctures are performed with a 20–23 g disposable hypodermic needle or a diamond corneal knife with the micrometer set at 0.10–0.2 mm (Fig. 8.9a). The hypodermic needle is grasped directly or clamped with a small hemostat to expose 0.1–0.2 mm of the tip. The needle should enter the cornea at a 45–90 angle. The 23 g hypodermic needle will penetrate deeper into the corneal stroma than the 20 g hypodermic needle. Alternatively, the Nd:YAG laser may be used with multiple impulses set at 2 mJ. About 15–25 punctures are usually made about 1.5 mm apart surrounding the erosion and extending into the adjacent normal cornea (Fig. 8.9b). The cornea is slightly indented when the 0.1–0.2 mm depth is achieved. If inadvertent complete puncture of the cornea results, rapid selfsealing occurs.

A

Superficial grid keratotomy In the superficial grid keratotomy procedure, the corneal epithelia and anterior stroma are incised numerous times in a grid, cross-hatching or linear pattern. The majority of the grid incisions are adjacent to the corneal erosion, but this procedure may cover most of the corneal surface. The linear incisions for superficial grid keratotomy are made with a 20 g disposable hypodermic needle, Beaver No. 6400 microsurgical blade, or a diamond knife with the micrometer set at 0.2–0.3 mm deep (Fig. 8.10a). Incisions at 90 to the first series of incisions complete the grid keratotomy (Fig. 8.10b). Smaller gauge hypodermic needles are not recommended, as their incisions extend too deep. The grids are about 1–1.5 mm apart.

Superficial linear keratotomy The superficial grid keratotomy procedure has been partially replaced by a linear keratotomy which is easier to perform in the clinical patient with only topical corneal anesthesia. In this modification, the corneal epithelia and superficial stroma are incised in vertical linear incisions using a 20–22 g hypodermic needle. The incisions, about 1 mm apart, overlap the corneal erosion by a few millimeters in all directions. As with the superficial punctate and grid keratotomies, smaller gauge hypodermic needles (smaller than 22 g) are avoided because of their tendency to penetrate too deeply. Postoperative management after these three procedures is topical broad-spectrum antibiotics instilled every 8 h for 5–7 days. Healing of the erosions should occur during this period. The success rate of these procedures for the treatment of recurrent corneal erosions in dogs is about 80–90% within 2 weeks.

B

Fig. 8.9 In the superficial punctate keratotomy procedure, multiple partial-thickness hypodermic needle punctures are made in the erosion and adjacent cornea. (a) After thumb forceps removal of the loose epithelia about the erosion, the epithelia and 0.1–0.2 mm of the anterior stroma are repeatedly partially penetrated with a 20 g hypodermic needle grasped with a hemostat to prevent deeper corneal penetration. (b) About 15–25 partial corneal punctures are positioned within the erosion and adjacent area.

A

B

Fig. 8.10 In the superficial grid keratotomy procedure, the corneal epithelia and anterior stroma are incised in a grid or cross-hatching manner within the corneal erosion and adjacent area. (a) The initial corneal incisions, about 0.1–0.25 mm deep, may be performed with the Beaver No. 6400 microsurgical blade, diamond knife or a disposable 20 g hypodermic needle. (b) A second set of crosshatching incisions are placed at 90 to the initial incisions. The grids should be 1.0–1.5 mm apart.

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Surgical procedures for deep corneal ulcerations

Alternative treatments appear to yield lower success rates. Treatment of canine recurrent erosions with only aqueous iodine cautery of the erosion requires an average of 46 days for complete re-epithelialization. Contact lenses for corneal erosions yield 73% success, the major limitation being retention of the lens. If the lens is retained for 7–10 days, the success rate increases to 92%. Other forms of treatment for this disorder include nictitating membrane flaps, temporary tarsorrhaphy, and bulbar conjunctival grafts (see Chapters 5 and 6). The success rates of these treatment methods have focused on short-term management of the healing of the recurrent erosions. The real value of these procedures, yet to be established, is long-term prevention of recurrent corneal erosions. Postoperative complications after superficial punctate and grid keratotomies are infrequent. Inadvertent puncture of the cornea is rare, after the technique has been mastered. Fortunately, these punctures will self-seal immediately, but a small corneal scar results. Both techniques may produce faint anterior stromal scars, appearing as individual spots or a grid. This scar formation is usually negligible when compared to the repeated effects of recurrent corneal erosions of the canine cornea, including influx of vascularization and pigmentation, and the occasional deposition of lipids, cholesterol, and calcium. Recently the clinical use of these different keratotomies in the cat has been questioned because of the development of corneal sequestrum following their use. Perhaps the feline herpes virus (FHV-1) is present in some corneal sequestra, and, following keratotomy, the virus can penetrate deeper into the stroma. As a result, pending further clinical studies, keratotomies in cats must be most cautiously performed.

Corneal biopsy Biopsy of the cornea is usually performed to establish a diagnosis. Diagnosis of specific infectious agents (bacterial/ fungal) and possible neoplasia is provided by corneal biopsy. Corneal biopsies may be limited to the anterior epithelium, anywhere in the stroma, or even full thickness. Under the rubric of corneal biopsies is corneal cytology (obtained by deep scraping), and superficial and deep keratectomies. Deep keratectomies are performed in the same manner as superficial keratectomies, but the surgical wound is usually covered with a bulbar conjunctival graft or corneal graft. Excisional corneal biopsies can combine both diagnosis and initial treatment. When ulcerated or inflamed cornea is biopsied, all necrotic and involved tissues should be excised to enhance the possibility of diagnosis, demonstrate infectious agents, and facilitate attachment and retention of the conjunctival graft. The corneal biopsy procedure is modified by the depth of the corneal disease: 1) superficial keratectomy for diseases of the epithelia and anterior one-half of corneal stroma; 2) deep keratectomy for corneal diseases involving the posterior one-half of the corneal stroma; and 3) full-thickness keratectomy with homologous corneal grafts when the entire depth of the cornea is involved. These surgical procedures are presented in the respective sections in this chapter.

Adaptation for large animals and special species Keratectomy to obtain tissue for culture or histology in melting ulcers is similar to the techniques used in small animals. Large amounts of necrotic cornea can be removed with tenotomy scissors to speed healing of melting ulcers in horses and cows. Stromal biopsies to aid in the diagnosis of stromal abscesses or immune-mediated keratopathies in horses can be obtained in the standing horse. Utilizing sedation and topical anesthesia, a linear incision in the corneal epithelium is made with the Beaver No. 6400 or 6900 microsurgical blade (Fig. 8.11). A Martinez corneal dissector is then used to separate the epithelium from the stroma. A small biopsy punch is utilized to obtain a stromal sample, and the tissue placed on a sponge in a histologic cassette in fixative. The corneal epithelium is sutured with 8-0 sutures in a simple interrupted pattern. Topical antibiotics and NSAIDs can be used post-biopsy.

Surgical procedures for deep corneal ulcerations Corneal ulcerations are frequent in dogs but less common in cats. In the dog, corneal ulcers may be initiated by minor trauma. In certain breeds, particularly brachycephalic dogs, corneal ulceration may be associated with several predisposing factors. In brachycephalic breeds the eye is very prominent, suffers lagophthalmia, and the rate of blinking may be less than normal. Corneal microtrauma may occur from distichia and nasal fold trichiasis. The precorneal film may be thin and abnormal centrally, placing the central corneal epithelia in constant jeopardy. Retention of rose Bengal by the central corneal epithelia in these dogs suggests that these cells are degenerating at a faster rate than normal. These eyes are frequently also victims of marginal or low levels of aqueous tear production. The combinative effect is the development of a central-to-paracentral corneal ulcer that rapidly becomes deeper and larger (Fig. 8.12). Clinical signs associated with pain are often minimal or absent. Initial medical treatment usually includes topical broad-spectrum antibiotics, topical autogenous serum, and mydriatics. If the corneal ulcer continues to progress to involve the deep corneal stroma, becomes a descemetocele, or perforates with iris prolapse, surgical treatment with conjunctival or corneal grafts is recommended. Maintenance of vision and the least corneal scarring are achieved when conjunctival grafts are positioned before development of corneal perforation and iris prolapse. Administration of antibiotic treatment to all potential corneal ulcerations is recommended. Surgical correction of these ulcerations will usually be successful, provided the infectious agents are eliminated. Bacteria, usually Staphylococcus and Streptococcus spp., are frequently isolated from canine corneal ulcers. These organisms seem to originate from the conjunctival surfaces. Staphylococcus spp. are usually susceptible to chloramphenicol, bacitracin, and gentamicin; Streptococcus spp. are usually susceptible to chloramphenicol, erythromycin, carbenicillin, and cephalothin. Infrequently recovered in small animals, Pseudomonas spp. are susceptible to gentamicin, tobramycin, polymyxin B, and amikacin.

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Surgery of the cornea and sclera

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Fig. 8.11 Corneal stromal biopsy in a horse with suspected immune-mediated keratitis. (a) Incision of the corneal epithelium in a sedated standing horse. (b) The corneal dissector is used to expose the corneal stroma. (c) Corneal forceps and scissors are used to remove a section of stroma for histopathology. d) Biopsy site is apposed by sutures.

Primary closure of small deep corneal ulcers Small deep corneal ulcers may be closed by direct suturing. The maximum diameter of corneal ulcers that can be apposed by sutures is about 3 mm or less. Control and hopefully

Fig. 8.12 Deep central corneal ulcer in a Pekingese dog. Primary closure with sutures of small and deep corneal ulcers (