LASEK, PRK, and Excimer Laser Stromal Surface Ablation (Refractive Surgery)

LASEK, PRK, AND EXCIMER LASER STROMAL SURFACE ABLATION

REFRACTIVE SURGERY Series Editors Dimitri T.Azar, M.D. Massachusetts Eye and Ear Infirmary Schepens Eye Research Institute and Harvard Medical School Boston, Massachusetts Douglas D.Koch, M.D. Cullen Eye Institute Baylor College of Medicine Houston, Texas 1. LASIK: Fundamentals, Surgical Techniques, and Complications, edited by Dimitri T.Azar and Douglas D.Koch 2. Hyperopia and Presbyopia, edited by Kazuo Tsubota, Brian S.Boxer Wachler, Dimitri T.Azar, and Douglas D.Koch 3. LASEK, PRK, and Excimer Laser Stromal Surface Ablation, edited by Dimitri T.Azar, Massimo Camellin, Richard W.Yee ADDITIONAL VOLUMES IN PREPARATION Phakic and Accomodating IOLs, edited by Steve Lane and Jose Guell

LASEK, PRK, AND EXCIMER LASER STROMAL SURFACE ABLATION edited by

Dimitri T.Azar Massachusetts Eye and Ear Infirmary Schepens Eye Research Institute and Harvard Medical School Boston, Massachusetts, U.S.A.

Massimo Camellin SEKAL Rovigo Micro Surgery Rovigo, Italy

Richard W.Yee Hermann Eye Center and University of Texas Health Science Center Houston, Texas, U.S.A. Associate Editors

Robert T.Ang, MD,Sandeep Jain, MD,TakujiKato, MD, PhD Jae-Bum Lee, MD, PhD,Ronald R.Krueger, MD Series Editors

Dimitri T.Azar, MD,Douglas D.Koch, MD

MARCEL DEKKER NEW YORK

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Preface Ignotum per ignotius [(To explain) the unknown by the more unknown] How important are the subtle technical details in improving the clinical outcomes of LASEK surgery? Is the reduction of wavefront error greater in LASEK and Epi-LASIK than in LASIK? Does alcohol kill the corneal epithelial cells or does it allow epithelial cell proliferation to occur divorced from the unwanted process of epithelial cell migration over a denuded stroma? These questions, and many others, have fueled the debate regarding LASEK and Epi-LASIK vs. PRK and LASIK. LASEK and Epi-LASIK are not universally employed refractive surgical procedures. They have several advantages over LASIK in patients with relatively thin pachymetry and in patients with borderline corneal topographical changes. However, the advantages of these techniques over PRK are yet to be established. Despite numerous anecdotal reports, clinical observations, and variations of surgical techniques suggesting certain advantages of LASEK and Epi-LASIK over PRK, other studies suggest possible advantages for PRK, at least in the early postoperative period. Clearly, large prospective randomized multi-center studies, carried out by experienced LASEK surgeons, are lacking. New techniques of LASEK also hold great promise to overcome some of its current limitations. Despite the apparent and sometimes unavoidable bias toward LASEK and surface ablation in many chapters of this book, the aim is not to present an argument favoring these techniques, but rather to present a panoramic view of various aspects of these techniques. We focus on the indications, contraindications, and surgical techniques of stromal surface ablation and discuss the postoperative care, wound healing, clinical outcomes, and complications. Also included are several basic chapters discussing wavefront analysis, optical aberration changes after LASEK, the effect of alcohol on corneal cell-cell and cell-matrix interactions, and the pathogenesis and treatment options for postoperative stromal haze. Inclusion of this book in our “Refractive Surgery Series” was initiated with the help of several of the associate editors, who had been postgraduate fellows at the Corneal and Refractive Surgery Service of the Massachusetts Eye and Ear Infirmary. Progress of this project was hindered by the lack of definitive answers to our questions in the peerreviewed literature. Completion of the first draft of the book would not have been possible without the efforts of Drs. Suphi Taneri and Puwat Charukamnoetkanok. Additional manuscripts from Drs. Massimo Camellin, Richard Yee, Ronald Krueger, and several other experienced LASEK surgeons provided more comprehensive coverage of the topic. We acknowledge the support of Dr. Geoff Greenwood and Rosemary Doherty of Taylor and Francis, Inc. and their commitment to this series dedicated to Refractive Surgery. We also thank Leona Greenhill for editorial assistance. Special thanks go to

Rhonda Harris, who has managed this project with utmost dedication, care, and attention to detail. We also thank the contributors for presenting the results of their investigations. Their work will not only help answer many important questions about LASEK and surface ablation, but also underscore the fact that many answers remain unknown. Yes, the field still suffers from explanations of the unknown by even more unknowns, but the observations (and opinions) of the contributors mark a step forward in the path of discovery in this important field. They pave the way for future scientific investigations, which will undoubtedly increase our understanding of LASEK and surface ablation and improve the visual outcomes of future patients undergoing conventional and customized keratorefractive surgery. Dimitri T.Azar Douglas D.Koch

Contents Preface

vi

Contributors

xii

1. Overview of LASEK and Stromal Surface Ablation Suphi Taneri, MD and Dimitri T.Azar, MD 2. Laser Subepithelial Keratomileusis (LASEK): Theoretical Advantages Over LASIK Paolo Vinciguerra, MD and Daniel Epstein, MD, PhD 3. Indications and Contraindications of LASEK Jae Bum Lee, MD, Puwat Charukamnoetkanok, MD and Dimitri T.Azar, MD 4. LASEK Preoperative Considerations Robin F.Beran, MD, FACS 5. LASEK Preoperative Evaluation Chun Chen Chen, MD and Dimitri T.Azar, MD 6. LASEK Techniques Chun Chen Chen, MD, Joel Javier, MD, and Dimitri T.Azar, MD 7. Camellin LASEK Technique Massimo Camellin, MD 8. Butterfly LASEK Puwat Charukamnoetkanok, MD and Suphi Taneri, MD 9. Epithelial Flap Hydrodissection and Viscodissection in Advanced Laser Surface Ablation (ALSA) Richard C.Rashid, MD 10. Surface Ablation Without Alcohol: Gel-Assisted LASEK and EpiLASIK using Epilift System Puwat Charukamnoetkanok, MD and Dimitri T.Azar, MD 11. Epi-LASIK: Surface Ablation Without Alcohol Ioannis G.Pallikaris, MD, PhD, Vikentia J.Katsanevaki, MD, Maria I. Kalyvianaki, MD, Irini I.Naoumidi, PhD, and Richard W.Yee, MD 12. Postoperative Management of LASEK Ahn Nguyen, MD, Amy Scally, OD, and Dimitri T.Azar, MD 13. LASEK Enhancements Lee Shahinian, Jr, MD

1 15

22

28 36 53 85 95 102

127

133

142 152

14. LASEK in High and Low Myopia Chris P.Lohmann, MD, PhD, David O’Brart, MD, Ann Patmore, BSC, John Marshall, PhD, Christoph Winkler von Mohrenfels, MD, Bernhard Gabler, MD, and Wolfgang Herrmann, MD 15. LASEK vs. PRK: Comparison of Visual Outcomes Minh Hanh Duong, MD and Damien Gatinel, MD 16. LASEK vs. LASIK: Comparison of Visual Outcomes Neal J.Peterson, MD, Alice Z.Chuang, PhD, Rajy M.Rouweyha, MD, and Richard W.Yee, MD 17. Topography-Based Aberration in LASEK vs. PRK and LASIK Michael K.Smolek, PhD, Stephen D.Klyce, PhD, Loan Nguyen, MD, Richard W.Yee, MD, John P.Stokes, MD, Marguerite B.McDonald, MD 18. LASEK Complications Jae Bum Lee, MD, PhD 19. Management of LASEK Complications Massimo Camellin, MD 20. Wavefront Analysis, Principles, and LASEK Application Ronald R.Krueger, MD, Patrick C.Yeh, MD, and Dimitri T.Azar, MD 21. Customized Ablation and LASEK Erin D.Stahl, MD and Daniel S.Durrie, MD 22. Comparison of Wavefront-Guided Photorefractive Keratectomy and LASEK Treatments for Myopia and Myopic Astigmatism Zoltán Z.Nagy, MD 23. Wound Healing After PRK, LASIK, and LASEK Takuji Kato, MD 24. Biochemical Basis of Epithelial Dehiscence and Reattachment After LASEK Eric E.Gabison, MD, Hailton B.Oliveira, MD, Jin-Hong Chang, PhD, and Dimitri T.Azar, MD 25. Refractive Surgical Wound Healing Mechanisms Revisited: A Glimpse at the Future of LASEK James V.Jester, PhD 26. Mitomycin C and Haze: Natural Progression Mujtaba A.Qazi, MD, Jay S.Pepose, MD, PhD, Irwin Y.Cua, MD, Saira A. Choudhri, MD, and M.Azim Mirza, MD 27. Mitomycin C and Surface Ablation Scott D.Barnes, MD and Dimitri T.Azar, MD 28. Use of Autologous Serum to Reduce Haze After LASEK Steven B.Yee, MD, Ning Lin, MD, OD, Alice Z.Chuang, PhD, and Richard W.Yee, MD 29. LASEK After Corneal and Intraocular Procedures Puwat Charukamnoetkanok, MD and Dimitri T.Azar, MD

156

170 176

192

211 224 235 259 270

276 289

300

313

343 354

365

30. LASEK After Penetrating Keratoplasty Steven B.Yee, MD, Ning Lin, MD, OD, Corey B.Westerfeld, MD, and Richard W.Yee, MD Index

371

381

Contributors Dimitri T.Azar, MD Massachusetts Eye and Ear Infirmary, Schepens Eye Research Institute, Harvard Medical School, Boston, MA Scott D.Barnes, MD Massachusetts Eye and Ear Infirmary, Schepens Eye Research Institute, Harvard Medical School, Boston, MA Robin F.Beran, MD, FACS Columbus Laser and Cataract Center, Columbus, OH Massimo Camellin, MD Sekal Rovigo MicroSurgery, Rovigo, Italy Jin-Hong Chang, PhD Massachusetts Eye and Ear Infirmary, Schepens Eye Research Institute, Harvard Medical School, Boston, MA Puwat Charukamnoetkanok, MD Massachusetts Eye and Ear Infirmary, Schepens Eye Research Institute, Harvard Medical School, Boston, MA Chun Chen Chen, MD Department of Ophthalmology, Taipei Municipal Jen-Ai Hospital, National Yang-Ming University, Taipei, Taiwan Saira A.Choudhri, MD Pepose Vision Institute, Chesterfield, MO Alice Z.Chuang, PhD Hermann Eye Center, Department of Ophthalmology and Visual Sciences, University of Texas Health Science Center at Houston, Houston, TX Irwin Y.Cua, MD Pepose Vision Institute, Chesterfield, MO Minh Hanh Duong, MD Service d’ophtalmologie, (Pr Hoang-Xuan), Hôpital Bichat, Fondation Rothschild, Université Paris VII, Paris, France Daniel S.Durrie, MD Durrie Vision Research, Overland Park, KS Daniel Epstein, MD, PhD Department of Ophthalmology, University Hospital, Zurich, Switzerland Eric E.Gabison, MD Massachusetts Eye and Ear Infirmary, Schepens Eye Research Institute, Harvard Medical School, Boston, MA Bernhard Gabler, MD University Eye Clinic, Regensburg, Germany Damien Gatinel, MD Service d’ophtalmologie, (Pr Hoang-Xuan), Hôpital Bichat, Fondation Rothschild, Université Paris VII, Paris, France Wolfgang Herrmann, MD University Eye Clinic, Regensburg, Germany Joel Javier, MD Massachusetts Eye and Ear Infirmary, Schepens Eye Research Institute, Harvard Medical School, Boston, MA James V.Jester, PhD Department of Ophthalmology, University of Texas Southwestern Medical Center at Dallas, Dallas, TX Maria I.Kaly vianaki, MD Vardinoyannion Eye Institute of Crete, University of Crete, Greece Takuji Kato, MD Juntendo University, Department of Ophthalmology, Tokyo, Japan Vikentia J.Katsanevaki, MD Vardinoyannion Eye Institute of Crete, University of Crete, Greece, University Hospital of Heraklion, Department of Ophthalmology, Crete, Greece Stephen D.Klyce, PhD LSU Eye Center, New Orleans, LA Ronald R.Krueger, MD Cole Eye Institute, Cleveland Clinic Foundation, Cleveland, OH

Jae Bum Lee, MD, PhD Massachusetts Eye and Ear Infirmary, Schepens Eye Research Institute, Harvard Medical School, Boston, MA Ning Lin, MD, OD Hermann Eye Center, Department of Ophthalmology and Visual Sciences, University of Texas Health Science Center at Houston, Houston, TX Chris P.Lohmann, MD, PhD University Eye Clinic Regensburg, Germany, The Rayne Institute, Department of Ophthalmology, St. Thomas Hospital, London, England John Marshall, PhD The Rayne Institute, Department of Ophthalmology, St. Thomas Hospital, London, England Marguerite B.McDonald, MD Southern Vision Institute, New Orleans, LA M.Azim Mirza, MD Pepose Vision Institute, Chesterfield, MO Zoltán Z.Nagy, MD 1st Department of Ophthalmology, Semmelweis University, Budapest, Hungary Irini I.Naoumidi, PhD Vardinoyannion Eye Institute of Crete, University of Crete, Greece Ahn Nguyen, MD Cornea and Refractive Surgery Service, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, MA Loan Nguyen, MD LSU Eye Center, New Orleans, LA David O’Brart, MD The Rayne Institute, Department of Ophthalmology, St. Thomas Hospital, London, England Hailton B.Oliveira, MD Massachusetts Eye and Ear Infirmary, Schepens Eye Research Institute, Harvard Medical School, Boston, MA Ioannis G.Pallikaris, MD, PhD Vardinoyannion Eye Institute of Crete, University of Crete, Greece, University Hospital of Heraklion, Department of Ophthalmology, Crete, Greece Ann Patmore, BSC The Rayne Institute, Department of Ophthalmology, St. Thomas Hospital, London, England Jay S.Pepose, MD, PhD Pepose Vision Institute, Chesterfield, MO; Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO Neal J.Peterson, MD Hermann Eye Center, Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, TX Mujtaba A.Qazi, MD Pepose Vision Institute, Chesterfield, MO; Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO Richard C.Rashid, MD Clinical Associate Professor of Ophthalmology, West Virginia University School of Medicine, Charleston Division, Charleston, WV Rajy M.Rouweyha, MD Hermann Eye Center, Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, TX Amy Scally, OD Cornea and Refractive Surgery Service, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, MA Lee Shahinian, Jr, MD Stanford University, Department of Ophthalmology, Stanford, CA Michael K.Smolek, PhD LSU Eye Center, New Orleans, LA Erin D.Stahl, MD Durrie Vision Research, Overland Park, KS John P.Stokes, MD Hermann Eye Center, Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, TX

Suphi Taneri, MD Zentrum für Refraktive Chirurgie, Munster, Germany Paolo Vinciguerra, MD Istituto Clinico Humanitas, Milan, Italy Corey B.Westerfield, MD Hermann Eye Center, Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, TX Christoph Winkler von Mohrenfels, MD University Eye Clinic, Regensburg, Germany Richard W.Yee, MD Hermann Eye Center, Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, TX Steven B.Yee, MD Hermann Eye Center, Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, TX Patrick C.Yeh, MD Massachusetts Eye and Ear Infirmary, Schepens Eye Research Institute, Harvard Medical School, Boston, MA LASEK, PRK, AND EXCIMER LASER STROMAL SURFACE ABLATION

1 Overview of LASEK and Stromal Surface Ablation Suphi Taneri, MD Zentrum für Refraktive Chirurgie Munster, Germany Dimitri T.Azar, MD Massachusetts Eye and Ear Infirmary, Schepens Eye Research Institute, Harvard Medical School Boston, MA

HISTORY Laser subepithelial keratomileusis (LASEK) (1–8) is a relatively new laser surgical procedure for the correction of refractive error that combines certain elements of both laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). The LASEK procedure is most commonly performed using dilute alcohol to loosen the epithelial adhesion to the corneal stroma. Laser ablation of the subepithelial stroma is performed before the hinged epithelial sheet is returned to its original position, as with the LASIK flap (Fig. 1). The flap-related LASIK complications and the slow visual recovery and haze risk of PRK may be avoided. The first LASEK procedure was performed at the Massachusetts Eye and Ear Infirmary in 1996 by one of us (DTA) (1). Camellin popularized the procedure and coined the term LASEK for laser epithelial keratomileusis (3,9). The history of LASEK can be traced back to the use of chemical agents to replace manual epithelial debridement in PRK, which was shown to produce scratches and nicking in the Bowman’s layer and to leave variable amounts of epithelium (10,11) (Table 1). Campos used 100% ethanol for 2 minutes on rabbit corneas and noted significant decrease in stromal keratocytes (27) Agrawal used 70% isopropyl alcohol for 2 minutes for epithelium removal in rabbit eyes and observed similar damage to the keratocytes (28). Helena et al. used 50% ethanol for 1 minute and observed increased keratocyte loss (29). A prospective study performed at the Massachusetts Eye and Ear Infirmary by Abad et al. showed that alcohol-assisted epithelial removal was a simple and safe alternative to mechanical epithelial removal before PRK (2). Other investigators using alcohol for epithelial removal included Stein et al., who were able to grasp, lift, pull apart, and split the corneal epithelium using two McPherson forceps (30), and Shah et al., who peeled the epithelium using a dry sponge (31). Carones et al. found significantly better results in terms of haze and corneal regularity in epithelial debridement using a 20% alcohol

LASEK, PRK, and excimer laser stromal surface ablation

2

solution compared to mechanical debridement (32). Other investigators focused on the formulation of ethanol (38.)

Figure 1 Schematic representation of conventional LASEK surgery showing the application of an epithelial trephine to delineate the edge of the epithelial flap (top left), alcohol application (top right), creation of an epithelial flap before laser ablation (bottom left), and replacement of the epithelial sheet over the ablated stroma (bottom right). Table 1. Milestones in LASEK History. 1982 Technique for obtaining sheets of intact rabbit corneal epithelium (Gipson) 1983 Excimer laser application on cadaver bovine corneas (Trokel and Srinivasan) 1984 Photorefractive experiments on animals (McDonald) 1985 PRK on a blind human eye (Seiler) 1987 PRK on a human sighted eye slated for exenteration 11 days after PRK (Seiler) 1988 PRK on a normal sighted eye (McDonald) 1989 Photoablation of fully sighted eyes and treatment on the underside of a free cap (Buratto)

Overview of LASEK and stromal surface ablation

3

1990 LASIK (Pallikaris) 1994 Hartmann-Shack wavefront sensing of human eye (Liang and Williams) 1996 Alcohol-assisted epithelial flap reattached over PRK (Azar) 1998 “LASEK” term coined, specialized equipment, and procedure popularized (Camellin) 1999 Customized corneal ablation (Seiler) 1999 Butterfly LASEK (Vinciguerra) 2000 Mitomycin C treatment of corneal haze after PRK in humans (Majmudar and Epstein) 2001 Hydrodissection and viscodissection (Rachid and Langerman) 2001 Gel-assisted LASEK (McDonald) 2002 Human epithelial cell viability in LASEK (Chen and Azar) 2002 Epi-LASIK (Pallikaris)

Camellin advocated the importance of a hypotonic solution obtained by diluting alcohol in distilled water for facilitating epithelial detachment (3), whereas Vinciguerra preferred balanced salt solution for dilution (8). Our group has investigated the mechanisms of epithelial reattachment in LASEK and the functional alterations of the cell membrane integrity and cell metabolism using livecell assays in vitro. Our studies suggested a dose- and time-dependent effect of alcohol on epithelial cells. The 25% concentration of alcohol was the inflection point of epithelial survival. Significant increase in cellular death occurred after 35 seconds of alcohol exposure. Forty seconds of exposure further induced apoptosis after 8 hours of incubation. Our studies on specimens obtained after conventional alcohol-assisted PRK showed that the epithelial cell layer is intact and the epithelial cells are still viable immediately after exposure to alcohol and surgical peeling. The presence of the basement membrane attached to the basal epithelial cell layer in many of our specimens indicates that the point of separation was between the basement membrane and Bowman’s layer (33,34).

TECHNIQUES AND TERMINOLOGY Several techniques of LASEK are described in this book, including the Camellin technique, the Vinciguerra butterfly technique, the McDonald technique, the Pallikaris Epi LASEK technique, and the Azar flap technique (Fig. 2). Additionally, several expressions have been used, including laser subepithelial keratomileusis (1,35,36), subepithelial photorefractive keratectomy (31,37), epithelial flap photorefractive keratectomy (7), laser-assisted subepithelial keratectomy (5,38), excimer laser subepithelial ablation (39), laser epithelial keratomileusis (39–41), and Epi-LASEK (42).

LASEK, PRK, and excimer laser stromal surface ablation

4

ADVANTAGES OF LASEK OVER PRK AND LASIK: EVIDENCEBASED COMPARISONS We have performed a meta-analysis to determine the advantages of LASEK over PRK and LASIK(14) (Table 2). LASEK may avoid several of the inherent complications including free caps, incomplete pass of the microkeratome, flap wrinkles, epithelial ingrowth, flap melt, interface debris, and diffuse lamellar keratitis after LASIK (22,46– 63), and postoperative pain, subepithelial haze, and slow visual rehabilitation after PRK (64–73). Our meta-analysis aimed at evaluating potential benefits and risks of LASEK and investigates the visual outcome in a semi-quantitative fashion showing distinct advantages (14): Safety One eye out of 907 (0.11%) lost two lines of Best Spectacle Corrected Visual Acuity (BSCVA). This was a loss observed in one of our patients on his final visit at 1 month from 20/20 to 20/30. Efficacy Uncorrected Visual Acuity (UCVA) of 20/20 or better at that time was achieved in 76% and of 20/40 or better in 99% (5,14,36,40). Predictability (Spherical Equivalent) The mean spherical equivalent of 152 eyes at 6-month follow-up was calculated to be −0.32 diopter (D)A (7,8,40). At 6-month follow-up, 83% of eyes (5,14,36,40) were within plusmn; 0.50 D and 98.35% of eyes were within ±1.00 D of desired postoperative refractive error (5,14,36). Stability Rouweyha et al. (40) reported a regression of approximately 2 D in 4 eyes of 2 patients (8% of their eyes) with visually significant haze at 6 months, whereas several other authors point out the absence of regression (3). The remarkable aspects of our review are the long-term stable results in complete absence of serious complications, like infections, recurrent erosions, scar, or late-onset corneal haze formation. Second, epithelial closure with recovery of functional vision could

Overview of LASEK and stromal surface ablation

5

Figure 2 (A) Overlapping circular marks are preplaced on the cornea. (B) 18% ethanol is released into the marker well. Care is taken to avoid spillage by using a dry sponge to absorb the overflowing ethanol. (C, D) A jeweler’s forceps is used to delineate the flap edges and locate the dissecting plane. (E, F) A dry, nonfragmenting sponge is used to peel the epithelial flap.

LASEK, PRK, and excimer laser stromal surface ablation

6

Figure 2 (CONT) (G) Laser ablation is applied to the exposed Bowman’s layer and stroma. (H, I) A 30-gauge Rycroft irrigating cannula is used to hydrate and reposition the epithelial flap. (J) Care is taken to realign the wound edges using the preplaced marks as a guide. (K) Flap edges are aligned, and no epithelial defects are noted after flap repositioning and during the 5-minute waiting period. (L) A bandage soft contact lens is applied at the end of the procedure.

Overview of LASEK and stromal surface ablation

7

be shown to happen at day 4 to day 7 in most cases. Third, we found a tendency toward overcorrection with PRK nomograms. Fourth, we may hypothesize that this tendency may be caused by the decreased wound healing response, which may lead to myopic regression in PRK. Last, postoperative pain and prolonged visual recovery until the epithelium closes remain the biggest disadvantages of LASEK compared to LASIK (14). (See Table 2.) A potential superiority of LASEK to LASIK in wavefront-guided ablations still remains speculative (Fig. 3). LASEK surgery is especially valuable in patients with thin corneas who would not qualify for LASIK surgery. Additionally, LASEK has become a viable option in patients with professions or lifestyles that predispose to flap trauma (contact sports athletes and military personnel) and in patients with low myopia who are at a lower risk for subepithelial haze.

Table 2. Widely Accepted Relative Differences Among PRK, LASIK, and LASEK. PRK

LASEK

LASIK

Range of correction

Low to moderately Low to moderately high Low to moderately high high

Postoperative pain

Moderate 24–48h (25)

Mild to moderate 24– 48h in approximately 50% (16)

Minimal 12h

Postoperative medications

3 wk to several months

3 wk to several mo

1 to 2 wk

Functional vision recovery

3 to 7 d

3 to 7 d

24 h

Refractive stability achieved

3 wk to several mo 3 wk to several mo

1 to 6 wk

Risk of complications

Low

Low to PRK (16)

Low (but higher with use of microkeratome)

Risk of scarring

1% to 2%

Possibly less than PRK

7

LASEK, PRK, and excimer laser stromal surface ablation

26

mm) in dim light because of the increased risk of night glare and halos (13). Advanced keratitis sicca with diffuse superficial punctate keratopathy or corneal filaments are a possible contraindication for LASEK. In LASEK, two essential components are the making of an epithelial flap and the use of contact lens. The production of tear film decreases with age. Older patients may find the postoperative contact lens uncomfortable. To maintain good adhesion of epithelial flap to stroma, patients should be instructed to avoid rubbing or blinking excessively, particularly during the first postoperative day.

GENERAL HEALTH Like all other refractive surgery procedures, the success of LASEK depends on proper wound healing. Any systemic conditions that may potentially be detrimental to the healing process of eyes should be actively uncovered during preoperative examination. Relative general contraindications are diabetes mellitus (type I and II), clinically significant atopy,

Table 2. Absolute Ocular Contraindications for LASEK. Keratoconus Monocular patients Severe dry eye (Sjögren syndrome) Active infection of cornea and conjunctiva Herpes zoster ophthalmicus

and pregnancy or lactation. During pregnancy or nursing, there may be hormonal changes that could alter the refractive errors and corneal haze (14). A recent study (15) has demonstrated a chance of regression 13.5 times higher in women using oral contraceptives. Patients should be warned of this apparent increased risk. Patients with active systemic connective tissue diseases (e.g., systemic lupus, rheumatoid arthritis) are considered poor LASEK candidates because of the potential for poor epithelial healing and the risk of a corneal melt. A history of keloid formation of the skin is no longer considered a contraindication to LASEK. History of keloid does not appear to increase risk of corneal haze. In our experience (6), contact lens intolerance after surgery occurred in 4% eyes, and most of these had folds in Decemet’s layer. Most patients were older than age 40 years. Although the reason for the contact lens intolerance is not clear, patients older than 40 should be informed of this increased risk. LASEK offers patients another choice of refractive surgery in mild to moderate myopia. It reduces the incidence of postoperative significant pain and corneal haze and could avoid various flap and interface-related problems after LASIK. However, careful patient selection is essential for successful outcome.

Indications and Contraindications of LASEK

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REFERENCES 1. Seiler T, Holschbach A, Derse M, Jean B, Genth U. Complications of myopic photorefractive keratectomy with the excimer laser.. Ophthalmology; 1994; 101:153–160. 2. Gartry DS, Kerr Muir MG, Marshall J. Excimer laser photorefractive keratectomy: 18 months follow-up.. Ophthalmology; 1992; 99:1209–1219. 3. Wang Z, Chen J, Yang B. Comparison of laser in situ keratomileusis and photorefractive keratectomy to correct myopia from −1.25 to −6.00 diopters.. J Refract Surg; 1997; 13:528–534. 4. Hersh P, Brint S, Maloney RK. Photorefractive keratectomy versus laser in situ keratomileusis for moderate to high myopia.. Ophthalmology; 1998; 105:1513–1523. 5. Camellin M. LASEK may offer the advantages of both LASIK and PRK.. Ocular surgery news international 1999; March. 6. Lee JB, Seong GJ, Lee JH, Seo KY, Lee YG, Kim EK. Comparison of laser epithelial keratomileusis and photorefractive keratectomy for low to moderate myopia.. J Cataract Refract Surg; 2001; 27:565–570. 7. Gabler B, vonMohrenfels W, Lohmann CP. LASEK: A histological study to investigate the vitality of corneal epithelial cells after alcohol exposure.. Invest Ophthalmol Vis Sci; 2001; 42:S560 [abstract 3222]. 8. Kornilovsky IM. Clinical results after subepithelial photorefractive keratectomy (LASEK).. J Refract Surg; 2001; 17(2Suppl):S222–S223. 9. Hori-Komai Y, Toda I, Tsubota K. Laser in situ keratomileusis: association with increased width of palpebral fissure.. Am J Ophthalmol; 2001; 131(2):254–255. 10. Farris RL. Contact lenses and the dry eye.. Int Ophthalmol Clin; 1994; 34(1):129–136. 11. Gimno JA, Munoz LA, Valenzuela LA, Molto FJ, Rahhal MS. Influence of refraction on tonometric readings after photorefractive keratectomy and laser assisted in situ keratomileusis.. Cornea; 2000; 19(4):512–516. 12. Arevalo JF, Ramirez E, Suarez E, Antzoulatos G, Morales-Stopello J, Ramirez G, Torres F, Gonzalez-Vivas R. Rhegmatogenous retinal detachment in myopic eyes after laser in situ keratomileusis. Frequency, characteristics, and mechanism.. J Cataract Refract Surg; 2001; 27(5):674–680. 13. Hersh PS, Steinnert RF, Brint SF. Photorefractive keratectomy versus laser in situ keratomileusis: comparison of optical side effects. Summit PRK-LASIK Study Group.. Ophthalmology; 2000; 107(5):925–933. 14. Sharif K. Regression of myopia induced by pregnancy after photorefractive keratectomy. J Refract Surg; 1997; 13(5Suppl):S445–S446. 15. McCarty CA, Ng I, Waldon B, Garrett SK, Downie JA, Aldred GF, Wolfe RJ, Taylor HR. Relation of hormone and menopausal status to outcomes following excimer laser photorefractive keratectomy in women. Melbourne Excimer Laser Group. Aust N Z J Ophthalmol; 1996; 24(3):215–222.

4 LASEK Preoperative Considerations Robin F.Beran, MD, FACS Columbus Laser and Cataract Center Columbus, OH

INTRODUCTION All refractive surgical procedures demand appropriate preoperative patient selection and patient preparation to achieve optimal postoperative results. This principle is extremely important when performing laser subepithelial keratomileusis (LASEK), because the characteristics of this technique are considerably different than the more popular procedure, laser in situ keratomileusis (LASIK). Patient selection includes consideration of candidate age, personality characteristics, occupational and recreational activities, as well as a number of specific ocular considerations. Preoperative patient preparation focuses on patient education and optimizing the ocular status for surgery. Failure to address these issues may reduce one’s chances for the best and safest outcome.

PATIENT CHARACTERISTICS The patient selection and evaluation process should begin with the initial patient contact. This contact is usually via phone, although there will be visitors and walk-ins. In addition to obtaining the vital personal information to permit continued contact, the staff member should record any comments regarding the encounter with the candidate that they believe to be pertinent. The candidate’s personality is important in determining which procedure is preferred, or even if one is a good refractive surgery candidate. An experienced and sharp staff member may pick up on personality characteristics that may be helpful. This awareness by the staff to access the patient’s interest and demeanor should persist throughout all aspects of the testing and evaluation process. The amount of contact time with the patient is limited and, thus, every minute is valuable. Table 1 summarizes certain personality traits that may favor LASEK vs. LASIK. Patient preference for the choice of procedure should never be overlooked. Many refractive surgeons are surprised at the number of patients who are uncomfortable and concerned about the idea of cutting a flap in their cornea. A significant portion of refractive surgery candidates has refrained from having laser vision correction because of safety concerns and lack of confidence. LASEK does satisfy some of these candidates’ fears regarding potential flap complications and potential for ectasia. Thus, providing LASEK as an option for patients can definitely increase the number of individuals electing to have surgery.

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Table 1. Patient Personality Characteristics. LASEK

LASIK

Well educated/informed

Obsessive/particular

Actively involved in process

Inpatient

Tolerant of pain

Poor pain tolerance

Eye rubber

Familiar with LASIK (friends/family)

Willing to accept slow visual recovery

There is nothing difficult about considering the lifestyle, occupational, and recreational characteristics with regard to the choice of a refractive surgical procedure. One simply needs to use common sense and weigh the overall advantages vs. the disadvantages for each procedure in that individual patient choosing the optimal for safety and visual improvement. Table 2 summarizes the lifestyle and occupational characteristics that may favor LASEK vs. LASIK. For younger patients, especially in their early 20s, it has been my belief that surface ablation offers the advantage of greater flexibility for future treatments if needed. The chance of a significant change in the refractive error of a 20-year-old over a lifetime is certainly much greater than that for a 40-year-old. Although we know that the LASIK flap can be successfully elevated after several years for an enhancement, there is most likely a time at which this cannot be accomplished. If an enhancement is desired in this situation, then one will be faced with the decision as to whether to re-cut a second flap or to perform surface ablation. The true consequences for each of these choices are not known at this time. Many photorefractive keratectomy (PRK) patients have had subsequent treatments after 6 or more years without any apparent complications. The considerations with regard to corneal instability and ectasia appear more important in LASIK enhancements and are not well-understood. For the younger patient with a life expectancy of 50 or 60 years, providing the greatest flexibility for the future does desire merit.

CLINICAL FINDINGS THAT MAY INFLUENCE THE CHOICE OF LASEK VS. LASIK The most common problems faced are deep-set eyes and small palpebral fissure width. In these situations, safe application of the vacuum ring and maintenance of adequate suction are often difficult with our present microkeratome systems. Therefore, with LASEK, one can safely eliminate the potential flap complication that might arise. The most common reason for choosing LASEK is the presence of an ocular characteristic not favorable for LASIK. Refractive surgeons have their own criteria for these ocular characteristics and for performing LASIK. Surgeon comfort levels for residual stromal bed range from 200 microns to 300 microns. Controversy exists over the degree of myopia (potential for stromal haze) safely treated with surface ablation. Others

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exist, and the following are those that seem important to use in accessing one’s candidacy for the procedures.

Table 2. Lifestyle and Occupational Characteristics. LASEK High risk for trauma

LASIK Minimal risk for trauma

Law enforcement

Golf

Firefighters

Swimming

Martial arts

Business professional

Basketball

Aerobics

Flexible schedule

Need for short recovery time

Easy access for follow-up

Long distance for follow-up Need to minimize risk of infection

Corneal Thickness Corneal thickness considerations are mandatory in the choice of laser vision correction procedure. The presence of inadequate corneal thickness in performing LASIK has the potential to lead to corneal instability and corneal ectasia. This has been documented in the literature over the past 3 years. There is still not a concrete understanding of the absolute limits and, as mentioned, surgeon comfort levels range from 200 microns to 300 microns of residual intact posterior stroma. Skeptics and those using lower amounts of tissue raise issues regarding the reported cases of ectasia and claim inaccurate microkeratome cuts, improper patient selection (early keratoconus), and incorrect measurements as reasons for this complication. At this time, it appears that the majority of surgeons feel comfortable with 250 microns of stroma as their limit. More conservative surgeons lean toward 300 microns as their limit. Another issue is the potential structural changes caused by the construction of a lamellar flap in a thin cornea. With lamellar keratoplasty for hyperopia, “controlled steepening (ectasia)” was achieved with a single, deep cut. A 160-micron flap in a 460micron cornea may possibly in and of itself create a degree of structural weakening. The best guideline at present seems to be using 500-micron total corneal thickness as the minimal limit for LASIK. To enable candidates who do not meet the aforementioned criteria to still undergo LASIK, surgeons will consider the use of a thinner corneal flap. Again, a number of questions arise, including the actual achieved flap thickness, the flap consistency of the microkeratome, potential for increased flap complications during construction, and a potential increase in striae or folds.

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Corneal Tissue Integrity and Quality Corneal tissue integrity and quality are important with respect to maintaining the strength of the cornea postoperatively. The only gauge available to access the quality or “normality” of the corneal tissue is topography. The presence of either the anterior or the posterior surface abnormalities suggestive of keratoconus can alert one to the likelihood of an abnormality of the stromal tissue. Unfortunately, the ability to routinely and simply obtain and analyze corneal tissue to identify abnormalities in the collagen structure is not available. Surface ablation is a better consideration for suspicious cases, because most would agree it is less likely than a lamellar procedure to induce weakening. Excessive Corneal Curvatures Excessive corneal curvatures can increase the risk of an intraoperative flap complication in LASIK. Either extremely steep (>48) or extremely flat (