The initial clinical application of the excimer

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1 Laser in Situ Keratomileusis for Myopia and Hyperopia Using the Lasersight 200 Laser in 300 Consecutive Eyes Victor E. Reviglio, MD; Erica L. Bossana, MD; José D. Luna, MD; Juan C. Muiño, MD; Claudio P. Juarez, MD ABSTRACT PURPOSE: To evaluate effectiveness, safety, predictability, and short-term stability of laser in situ keratomileusis (LASIK) using the LaserSight Compac-200 Mini excimer laser with software version 9.0, for all refractive errors. METHODS: One hundred fifty consecutive patients (300 eyes) that received bilateral LASIK for myopia, hyperopia, and astigmatism were studied prospectively. A new 9.0 software version applying a modified nomogram that takes advantage of bilateral surgery was used. Follow-up at 6 months was available for 267 eyes (89%). RESULTS: Six months postoperatively, 131 eyes (96.32%) in the low to moderate myopia group (-1.00 to D; n=136) had a spherical equivalent refraction within ±1.00 D, and 123 eyes (90.44%) were within ±0.50 D of emmetropia. In the high to extreme myopia group (-6.00 to D; n=114), 97 eyes (87.08%) had a spherical equivalent refraction within ±1.00 D and 78 eyes (68.42%) were within ±0.50 D of emmetropia. In the hyperopia group (+1.00 to D; n=50), 44 eyes (88%) had a postoperative spherical equivalent refraction within ±1.00 D, and 31 eyes (62%) were within ±0.50 D of emmetropia. Mean change in spherical equivalent refraction at 6 months was less than D in the low to high myopia groups and ± 0.55 D in the extreme myopia group. At 6 months follow-up, uncorrected visual acuity was 20/20 or better in 73 eyes (54%) in the low to moderate myopia groups and 21 eyes (18%) in the high to extreme myopia groups. In the hyperopia group at 6 months followup, uncorrected visual acuity was 20/20 or better in 31 eyes (62%) and 20/40 or better in 41 eyes (82%). Only two eyes had a temporary loss of two or more lines of spectacle-corrected visual acuity due to corneal folds that were surgically treated. Six months after LASIK, no eye had lost any lines of best spectacle-corrected visual acuity in this series. From the Fundación VER, Córdoba, Argentina. The authors have no proprietary interest in any materials or methods presented in this article. Correspondence: Claudio P. Juárez, MD, Fundación VER, Dean Funes 432, PO Box 743, 5000 Córdoba, Argentina. Tel: ; Fax: ; funver@powernet.com.ar Received: August 13, 1999 Accepted: July 19, 2000 CONCLUSIONS: Our modified LASIK nomogram with the 9.0 software of the LaserSight 200 excimer laser (with a larger and smoother ablation pattern) resulted in safe and effective outcomes for the treatment of low to high myopia, astigmatism, and hyperopia. [J Refract Surg 2000;16: ] The initial clinical application of the excimer laser was for photorefractive keratectomy (PRK) 1-3 and visual results and complications have been reported in numerous clinical studies. 4-7 In situ keratomileusis with a manual microkeratome was first introduced by Ruiz. 8 Laser in situ keratomileusis (LASIK) is considered a safe and effective refractive procedure for correction of myopia, hyperopia, and astigmatism The main advantages of LASIK, compared to photorefractive keratectomy (PRK) 12,13 and radial keratotomy proved to be markedly reduced postoperative pain and discomfort, rapid recovery of useful visual acuity, lower incidence of abnormal epithelial and stromal corneal wound healing (haze), and refractive stability over a longer period of time The original surgical technique has evolved markedly, mainly with step-by-step improvements in surgical technique and microkeratomes, as well as with the development of better excimer laser units with small spot beams and trackers, scanning devices, and the more recent customized ablations. 20,21 There are, however, many factors that may facilitate more improvements, maximizing the final vision and making results more predictable. 22,23 The learning curve of surgical skills is noticeable, and there is now growing evidence that excimer laser units do not work equally in different and even in similar environments. Many excimer laser units have fixed software installed by the manufacturers, and the majority of LASIK surgeons face the difficult but necessary task of developing their own nomograms. In this prospective study, we present the short-term stability and effectiveness of bilateral LASIK performed on our initial 300 consecutive eyes with a 716 Journal of Refractive Surgery Volume 16 November/December 2000

2 previously modified nomogram, using the LaserSight Compac-200 Mini excimer laser with software version 9.0. PATIENTS AND METHODS Patient Selection and Study Design The charts of all patients from our eye department undergoing bilateral LASIK surgery for the correction of myopia, hyperopia, and astigmatism, were followed consecutively from September 1998 to April Three hundred eyes of 150 patients (72 male, 78 female) with a mean age of 35.2 ± 6.75 years (range, 21 to 61 yr) were followed for 6 months (mean, 5.1 mo; range, 1 wk to 6 mo). After surgery, 294 eyes (98%) were examined at 1 month, 288 eyes (96%) at 3 months, and 267 eyes (89%) at 6 months. The eyes were divided for statistical analysis into four myopia groups (low, moderate, high, extreme) and two hyperopia groups (low, high) depending on baseline spherical equivalent refraction. Mean astigmatism for each myopia group was recorded as well. Lindstrom's classification was used 24 : low myopia (74 eyes; to diopters [D]); moderate myopia (62 eyes; to D); high myopia (63 eyes; to D); extreme myopia (63 eyes; to D). There were 33 eyes in the low hyperopia group (+1.00 to D) and 17 eyes in the high hyperopia group (+3.25 to D). Inclusion criteria for surgery were stable refraction and age 19 years or older. There were no patients with a history of prior refractive, cataract, or vitreo-retinal surgery, keratoconus, uncontrolled glaucoma, uveitis, autoimmune disease, proliferative diabetic retinopathy, or other systemic diseases. Patients with cardiac disorders and pregnant women were also excluded. Preoperative Examination The following examinations were performed preoperatively in all patients to satisfy the inclusion criteria: uncorrected and spectacle-corrected Snellen and Logmar visual acuity by manifest refraction (with and without cycloplegia), ocular external and internal motility, slit-lamp biomicroscopy, applanation tonometry, Schirmer test, and detailed fundus examination with direct and indirect ophthalmoscopy (28 D and 90 D), keratometry, pachymetry, and corneal topography (Alcon Eye Map, Ft. Worth, TX). All measurements were performed by the staff at Centro Privado de Ojos Romagosa, and the results were reviewed by one of the team surgeons (CPJ). Informed consent was obtained from all patients after an extensive and detailed explanation of the procedure and its potential risks and benefits, particularly regarding bilateral surgery as it was done in the authors previous published study. 25 Surgical Technique All surgeries were carried out by a team of two experienced refractive surgeons (CPJ and VER). The authors have several years experience in keratomileusis and have performed more than 1000 LASIK cases yearly since they acquired the excimer laser in early A LaserSight 200 excimer laser (LaserSight, Orlando, FL) with software version 9.0 (December 1997) was used for all eyes. The laser used an ArF 193 nm excimer beam, 160 mj/cm 2, with a 0.9 mm beam diameter and a scanning device. The ablation rate and pattern (randomized) were provided by fixed software and minor changes could be made. The laser unit also provides a sequential overlapping ablation pattern which was not used in this series. The standard algorithm included in the software of the LaserSight 200 excimer laser was adjusted according to the close parameters of the software and previous nomograms made by the surgeons in order to improve our results. 26 The ablation zone diameter used in all eyes for myopia was 5.5 mm with a 6.5-mm transition zone, and for astigmatism and hyperopia, we used a 6-mm ablation zone with an 8.5-mm transition zone. For myopic eyes, from the original manufacturer's nomogram we subtracted 10% of the original manifest sphere without change in cylindrical value for low myopia, 15% for moderate myopia, and 20% for high and extreme myopia. For treatment parameters for hyperopia we added 20% of the manifest sphere to the manufacturer s nomogram. The polymethylmethacrylate (PMMA) calibration was done with the calibration unit. Once the final values were entered into the laser computer software and the laser was considered properly centered, LASIK was performed. An 9.0 to 9.5-mm diameter, 130-µm or 160-µm thick, anterior corneal flap was created using the Automated Corneal Sharper (Chiron Vision, Claremont, CA; now Bausch & Lomb), depending on preoperative corneal thickness and amount of planned refractive correction. The suction ring had been modified at the laser center and had been used successfully for 4 years before this study. The maximum ablation depth was calculated so the remaining corneal stromal bed after lifting the flap was more than 250 µm. A specially designed corneal marker was used to avoid problems of cyclorotation Journal of Refractive Surgery Volume 16 November/December

3 Table 1 Data of Eyes That Received LASIK With the LaserSight 200 Excimer Laser Baseline No. Sex (F/M) Mean Age Preoperative Refraction (D) Postoperative Refraction (D) 6 Mo Groups Eyes ± SD (yr) Mean spherical equivalent ± SD Mean spherical equivalent ± SD (range) Low myopia (-1.00 to D) 74 39/ ± ± ± 0.41 (22 to 53) Moderate myopia (-4.00 to D) 62 25/ ± ± ± 0.74 (21 to 38) High myopia (-6.00 to D) 63 27/ ± ± ± 0.92 (21 to 43) Extreme myopia ( to D) 51 36/ ± ± ± 1.23 (27 to 50) Low hyperopia (+1.00 to D) 33 22/ ± ± ± 0.21 (36 to 60) Moderate hyperopia (+3.00 to D) 17 7/ ± ± ± 0.88 (24 to 61) during the surgery and ensure proper and accurate corneal flap alignment after surgery. The suction ring was applied and centered, with the pupil considered the eye's anatomical center. A C-shaped corneal flap was created using a previously adjusted microkeratome stopper. No eye-tracking device was used. During the laser ablation procedure, the surgeon controlled globe fixation and axis alignment using a specially designed fixation ring. Following the ablation, the interface and flap were irrigated mildly with balanced saline solution with a blunttipped, curved LASIK cannula to remove any possible debris or epithelial cells, and the flap was replaced and aligned to its original position with the same cannula. Air was applied to the flap for a few seconds with a transparent modified eye shield canula with multiple inside air openings that distribute air in a uniform fashion to the surface of the flap. We allowed 3 minutes for the flap to stick to the corneal stromal bed. Next, topical tobramicin 0.3% with dexamethasone 0.1% drops were applied, and a protective shield was used postoperatively to prevent rubbing or touching of eyes. Thirty minutes after surgery, the flaps were examined by the surgeon with slit-lamp biomicroscopy to ensure proper positioning. No eyepatches or soft contact lenses were used. Postoperative treatment included topical tobramicin 0.3% with dexamethasone 0.1% four times daily for 10 days. Artificial tears were prescribed four times daily for 1 month to avoid corneal dryness. Postoperative Examination Follow-up examinations were scheduled for 1 day, 1 week, and 3 and 6 months. Postoperative examinations consisted of slit-lamp biomicroscopy, measurement of manifest refraction, uncorrected, and best spectacle-corrected visual acuity. RESULTS Refractive Findings Baseline refractive data for the myopia and hyperopia groups are summarized in Table 1. At 6 months after LASIK, the low myopia group (-1.00 to D) had a mean postoperative spherical equivalent refraction of ± 0.41 D, the moderate myopia group (-4.00 to D) ± 0.74 D, the high myopia group (-6.00 to D) ± 0.92 D, and the extreme myopia group ( to D) ± 1.23 D. In the low hyperopia group (+1.00 to D) at 6 months after LASIK, mean postoperative spherical equivalent refraction was ± 0.21 D and in the high hyperopia group (+3.00 to D), mean postoperative spherical equivalent refraction was ± 0.88 D. No eyes in the hyperopia groups were retreated for under- or overcorrections. Six months after LASIK, in the low and moderate myopia groups (n=176), 131 eyes (96.32%) had refractive errors within ±1.00 D of emmetropia, and 123 eyes (90.44%) were within ±0.50 D of 718 Journal of Refractive Surgery Volume 16 November/December 2000

4 emmetropia. For the high and extreme myopia groups (n=114), 97 eyes (85.08%) were within ±1.00 D, and 78 eyes (68.42%) were within ±0.50 D of emmetropia (Fig 1). In the low and moderate hyperopia groups (n=50), 44 eyes (88%) were within ±1.00 D of emmetropia and 31 eyes (62%) were within ±0.50 D of emmetropia. The mean change in spherical equivalent refraction observed at 6 months after LASIK was ± 0.32 D in the low, moderate, and high myopia Figure 1. Change in mean spherical equivalent refraction between the first and sixth month after surgery according to preoperative amount of myopia. Table 2 Baseline Visual Acuity in 250 Eyes groups. In the extreme myopia group there was still some regression within 2 months after surgery (mean, ± 0.55 D). Almost all the retreatments were done within 2 months with the excimer laser. Even though there was a temporary loss of best spectacle-corrected visual acuity in the two retreated eyes, no permanent loss of baseline best spectacle-corrected visual acuity was observed in any patient. Visual Acuity Tables 2 and 3 and Figure 2 detail visual acuity before and after LASIK in 250 myopic eyes with 6 months follow-up. We observed a postoperative improvement of best spectacle-corrected visual acuity (BSCVA) in some eyes between the first and third months. Other authors report similar improvements in BSCVA in myopic patients after LASIK. Figure 3 shows the change in spectacle-corrected visual acuity 6 months after surgery in the myopia groups. Only two eyes (0.66%) temporarily lost 2 or more lines of best spectacle-corrected visual acuity. These losses (20/20 to 20/40 and 20/25 to 20/40) were attributable to corneal folds, and required immediate postoperative treatment. However, at 6 months follow-up, no eye had lost any lines of best spectacle-corrected visual acuity in this series. Group No. Uncorrected No. Eyes (%) Spectacle-corrected No. Eyes (%) Eyes 20/20 20/25 20/40 20/200 20/20 20/25 20/40 20/200 Low myopia (40.5) 44 (59.5) 50 (67.6) 11 (14.9) 13 (17.5) 0 (-1.00 to D) Moderate myopia (11.3) 55 (88.7) 43 (69.3) 13 (21) 4 (6.5) 2 (3.2) (-4.00 to D) High myopia (6.35) 59 (93.65) 24 (38.1) 25 (39.7) 12 (19) 2 (3.2) (-6.00 to D) Extreme myopia (100) 6 (11.8) 15 (29.4) 20 (39.2) 10 (19.6) ( to D) Table 3 Visual Acuity in 250 Eyes 6 Months After LASIK Group No. Uncorrected No. Eyes (%) Spectacle-corrected No. Eyes (%) Eyes 20/20 20/25 20/40 20/200 20/20 20/25 20/40 20/200 Low myopia (60.8) 15 (20.3) 14 (18.9) 0 52 (70.2) 13 (17.6) 9 (12.2) 0 (-1.00 to D) Moderate myopia (45.2) 20 (32.3) 11 (17.7) 3 (4.8) 46 (74.2) 11 (17.7) 4 (6.5) 1 (1.6) (-4.00 to D) High myopia (25.4) 18 (28.5) 21 (33.3) 8 (12.8) 26 (41.2) 27 (42.9) 9 (14.3) 1 (1.6) (-6.00 to D) Extreme myopia 51 5 (9.8) 9 (17.6) 26 (51) 11 (21.6) 10 (19.6) 19 (37.2) 16 (31.4) 6 (11.8) ( to D) Journal of Refractive Surgery Volume 16 November/December

5 A B C D Figure 2. Postoperative uncorrected and spectacle-corrected visual acuity at 6 months after LASIK. A) low myopia group, B) moderate myopia group, C) high myopia group, D) extreme myopia group. preoperative astigmatism was ± 0.72 D (range, 0.50 to 3.00 D) and postoperatively, it was ± 0.25 D (range, 0 to 0.75 D) at 6 months. Corneal topography and keratometry studies did not show irregular astigmatism; the amount of axis deviation did not exceed 10 in 282 eyes (94%) at 6 months after surgery. Figure 3. Percent of myopic eyes with gain or loss of Snellen lines of spectacle-corrected visual acuity 6 months after LASIK. Astigmatism All patients have some amount of irregular astigmatism in the early postoperative period (first week), especially those requiring higher corrections of myopia or hyperopia. However, the most important factor is the experience of the surgeons with the surgical technique to reduce the incidence of irregular astigmatism associated with flap alignment. In this study, before surgery, 234 eyes (78%) had mean compound myopic astigmatism of ± 1.78 D (range, 0.75 to 6.75 D). Six months after surgery, compound myopic astigmatism was present in 63 eyes (21%; mean, ± 0.52 D; range, 0.25 to 1.25 D) (Table 4). In the 50 hyperopic eyes, mean Complications In this study, refractive complications related to preoperative parameters, such as moderate overcorrections, were the most common complications, especially in the high and extreme myopia groups. This was followed by some regression that occurred mainly during the first 15 days after surgery. There were no corneal topography or symptomatic decentrations associated with the surgical technique. Some patients had a large angle kappa, and minimal decentrations were revealed by postoperative routine corneal topography because the ablation was shifted in the visual axis. The clinical appearance of the eye during the first few hours and day 1 postoperatively is critical to detect potential or serious complications with LASIK. During postoperative slit-lamp examination, unusual debris in the interface could be observed at high magnification. None of these 720 Journal of Refractive Surgery Volume 16 November/December 2000

6 Table 4 Astigmatism (Manifest Refraction) Before and 6 Months After LASIK for Myopia Myopia Baseline (D) Postoperative (D) Group Mean ± SD (range) Mean ± SD (range) Low ± ± 0.41 (-1 to D) (+0.25 to +4.25) (0 to +0.75) Moderate ± ± 0.66 (-4 to D) (+0.25 to +5.50) (0 to +1.00) High ± ± 0.54 (-6 to D) (0.50 to +6.75) (+0.25 to +1.25) Extreme ± ± 0.33 (-10 to -25 D) (+0.50 to +5.75) (+0.50 to +1.25) particles had visual or refractive consequences. Thinner flaps (130 µm) predisposed the eye to interface particles and microfolds. Six hyperopic eyes (2%) showed epithelial ingrowth in the wound edges (less than grade 0.5) associated with free caps (2%), none of which required surgical removal. Haze was not present, nor incomplete cuts, corneal ectasia, keratitis, or infection. Early postoperative corneal epithelial erosion was present in eight eyes (2.67%) associated with excessive use of topical anesthetic and were managed successfully with bandage contact lenses for 24 hours. Only two eyes (0.66%) lost two or more lines of spectacle corrected visual acuity due to corneal folds (patients rubbing their eyes). The flaps were repositioned within the first 24 hours after LASIK. Reoperations The majority of retreatments were due to lack of precision of the primary LASIK procedure, associated with early experience with the new software nomogram. These retreatments were performed in 15 eyes (5%) of the extreme myopia group that experienced overcorrection after surgery, and underwent a repeat procedure within the following 30 to 45 days. Enhancements were performed according to the patients' needs, age, accommodative power, and status of the other operated eye. No other corrections were required later, due to the use of the new preset nomograms for the high and extreme myopia groups. DISCUSSION LASIK is widely accepted as a safe refractive procedure for the correction of refractive errors; we also believe it to be safe for bilateral surgery. However, the surgical learning curve requires substantial training and experience to avoid complications. Complications have been described in a few published reports which point out the need to acquire experience in the handling of the microkeratome In the current study, the surgeons experience is reflected by the absence of microkeratome related complications, or flap complications such as flap wrinkles, shrinkage, and/or buttonholes. We presently use LASIK for the correction of all refractive errors with the LaserSight 200 and the software version 9.0. Details of the surgical technique and the results of refractive error correction by the 8.51 software version have been reported. 25 For the purpose of statistical analysis this study controlled whole variables by having the same equipment, two surgeons using similar surgical technique and similar ablation nomograms to evaluate the effectiveness, predictability, and stability of the new software. Taking advantage of bilateral surgery, the authors compared minor refractive defects found with the surgery and then applied the suspected under- or overcorrection needed to two statistically identical groups of about 16 patients. The only variable was one eye left with the preexisting nomogram and the opposite eye with the suspected under- or overcorrection. 26 Since LASIK surgery has been shown to be fairly stable by 2 weeks after surgery, we also think a 2 to 3 month period is enough to determine if the nomogram worked in these statistically similar groups of patients. We used a similar technique to demonstrate that the previous randomized ablation patterns grossly overcorrected sphere in high myopes. 26 The main advantages of the new 9.0 software compared to the old 8.51 version include reduced photoablation time, smoother stromal surface, (change from sequential to randomized photoablation), and larger ablation zone treatment. These advantages are most likely the key to obtain accurate refractive stability. Clinical and experimental studies suggest that corneal smoothness and lower ablation depth rate yield a more satisfactory visual outcome. 20 Our experience during the first 2 months using the new software indicates that current LASIK nomograms require adjustments for the Journal of Refractive Surgery Volume 16 November/December

7 treatment of high and extreme myopia to avoid overcorrections. These overcorrections may result from the use of a larger ablation zone and the new randomized photoablation pattern featured in the 9.0 software. This pattern is characterized by avoiding overlapping ablation and performing smoother photoablation of the corneal stromal surface. The laser nomograms had to be adjusted on the basis of refractive and clinical results, and no high over- or undercorrections were noted in later procedures. In our series, the refraction was stable between the third to sixth month after surgery, but continued follow-up is necessary to confirm 1-year stability. In some extreme myopia treatments, 130-µm flap thicknesses are used and larger amounts of cornea must be ablated, which produces greater surface irregularity and may increase the incidence of irregular astigmatism, dehydration effects, corneal opacification, and keratectasia. 34 These LASIK patients may experience myopic regression despite the fact that LASIK wound healing is localized mainly at the corneal stroma, avoiding epithelialstromal interaction (as in photorefractive keratectomy). Recent studies indicate that regression may be due to epithelial hyperplasia and stromal remodeling, associated with preservation of Bowman s layer. 23,35 Vesaluoma and colleagues (Vesaluoma H, Petroll WM, Perez-Santonja JJ, Linna TV, Alio JL, Tervo T. LASIK flap margin: wound healing and complications imaged by in vivo confocal microscopy. Invest Ophthalmol Vis Sci 2000;41(suppl):S458) hypothesized that the lamellar cut at the level of the most anterior layer (thin flaps) predisposes the cornea to pronounced and prolonged anterior keratocyte activation with increased corneal reflectivity from abnormal extracellular matrix deposition. The refractive predictability and stability of the procedure begin to diminish in these cases, and it is important to understand the absence of reversibility of corneal refractive surgery. The surgeon should bear in mind the different surgical procedures available for the treatment of extremely myopic eyes and discuss the choice with the patient to evaluate the acceptable risk in relation to the optical correction. We use LASIK for treatment of refractive errors with the new software 9.0, and our preliminary results show that refractive corrections stabilize by 3 months, with good accuracy of treatment of refractive errors. REFERENCES 1. Trokel SL, Srinivasan R, Braren B. 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8 22. Barraquer IS, O'Brien TP. Laser-assisted in-situ keratomileusis. In: Gottsch JD, Stark W, Goldberg MF, eds. Rob & Smith Operative Surgery. Ophthalmic Surgery. 5th Ed. New York, NY: Oxford Univ Press, Inc; 1999: Del Pero RA, Gigstad JE, Roberts AD, Klintworth GK, Clifford AM, L'Esperance FA, Taylor DM. A refractive and histopathologic study of excimer laser keratectomy in primates. Am J Ophthalmol 1990; 109: Lindstrom RL. The Barraquer lecture: surgical management of myopia Clinician's perspective. J Refract Surg 1997;13: Reviglio VE, Luna JD, Rodríguez ML, García FE, Juárez CP. Laser in situ keratomileusis using the LaserSight 200 laser: Results of 950 consecutive cases. J Cataract Refract Surg 1999;25: Reviglio VE, Bossana EL, Luna JD, Juarez CP. Cirugía bilateral: El mejor modo de realizar nomogramas personalizados de LASIK. Rev Fac Cienc Med Córdoba 2000;57: Chayet AS, Assil KK, Montes M, Castellanos A. Laser in situ keratomileusis for hyperopia: new software. J Refract Surg 1997;13(suppl):S434-S Knorz MC, Liermann A, Seiberth V, Steiner H, Wiesinger B. Laser in situ keratomileusis to correct myopia of to diopters. J Refract Surg 1996;12: Gomes M. Laser in situ keratomileusis for myopia using manual dissection. J Refract Surg 1995; 11(suppl): S239-S Perez-Santoja JJ, Bellot J, Claramonte P, Ismail MM, Alió JL. Laser in situ keratomileusis (LASIK) for the correction of high myopia. J Cataract Refract Surg 1997;23: Fiander DC, Tayfour F. Excimer laser in situ keratomileusis in 124 myopic eyes. J Refract Surg 1995;11(suppl): S234-S Marinho A, Pinto MC, Pinto R, Vaz F, Neves MC. LASIK for high myopia: one year experience. Ophthalmic Surg Lasers 1996;27(suppl):S517-S Gimbel HV, Anderson Penno EE, van Westenbrugge JA, Ferensowicz M, Furlong MT. Incidence and management of intraoperative and early postoperative complications in 1000 consecutive laser in situ keratomileusis cases. Ophthalmology 1998;105: Seiler T, Koufala K, Ritcher G. Iatrogenic keractectasia after laser in situ keratomileusis. J Refract Surg 1998;14: Tuft SJ, Zabel RW, Marshall J. Corneal repair following keratectomy. A comparison between conventional surgery and laser photoablation. Invest Ophthalmol Vis Sci 1989;30: Journal of Refractive Surgery Volume 16 November/December