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PURPOSE: To report a case of corneal ectasia after laser in situ keratomileusis (LASIK). The patient presented with minimal alterations in manifest refraction but had obvious distortions in the wavefront error of the eye, as demonstrated by InterWave aberrometry. METHODS: Retrospective case report and literature review. RESULTS: Three years following uneventful and initially successful LASIK and two subsequent enhancement procedures, a patient experienced a decrease in uncorrected and best spectacle-corrected visual acuity with only minor changes in manifest refraction and initially subtle changes on corneal topography. InterWave aberrometry showed a wavefront distortion consistent with progressive steepening of the anterior cornea, reflecting possible development of corneal ectasia. CONCLUSIONS: InterWave aberrometry in conjunction with corneal topography was useful for early recognition of the development of corneal ectasia after LASIK. [J Refract Surg 2004;20: 170-175]

Visual aberrations such as glare and halo have been well documented after laser in-situ keratomileusis (LASIK). These are more likely in patients with higher refractive errors and large pupil diameters. We present a patient with good Snellen acuity but functional impairment by visual aberrations after LASIK. These symptoms resolved after an InterWave-guided LASIK multipass, multistage enhancement treatment to correct spherical aberrations.

To review cases of corneal ectasia after laser in situ keratomileusis (LASIK), identify preoperative risk factors, and evaluate methods and success rates of visual rehabilitation for these cases.Retrospective nonrandomized comparative trial.Ten eyes from seven patients identified as developing corneal ectasia after LASIK, 33 previously reported ectasia cases, and two control groups with uneventful LASIK and normal postoperative courses: 100 consecutive cases (first control group), and 100 consecutive cases with high myopia (8 diopters [D]) preoperatively (second control group).Retrospective review of preoperative and postoperative data for each case compared with that of previously reported cases and cases with uneventful postoperative courses.Preoperative refraction, topographic features, residual stromal bed thickness (RSB), time to the development of ectasia, number of enhancements, final best-corrected visual acuity (BCVA), and method of final correction.Length of follow-up averaged 23.4 months (range, 6-48 months) after LASIK. Mean time to the development of ectasia averaged 16.3 months (range, 1-45 months). Preoperative refraction averaged -8.69 D compared with -5.37 D for the first control group (P = 0.005). Preoperatively, 88% of ectasia cases met criteria for forme fruste keratoconus, compared with 2% of the first control group (P0.0000001) and 4% of the second control group (P = 0.0000001). Seven eyes (70%) had RSB250 microm, as did 16% of eyes in the first control group and 46% of the second control group. The mean RSB for ectasia cases (222.8 microm) was significantly less than that for the first control group (293.6 micro m, P = 0.0004) and the second control group (256.5 microm; P = 0.04). Seven eyes (70%) had enhancements. Only 10% of eyes lost more than one line of BCVA, and all patients eventually achieved corrected vision of 20/30 or better. One case required penetrating keratoplasty (10%), while all others required rigid gas-permeable contact lenses for correction.Significant risk factors for the development of ectasia after LASIK include high myopia, forme fruste keratoconus, and low RSB. All patients had at least one risk factor other than high myopia, and significant differences remained even when controlling for myopia. Multiple enhancements were common among affected cases, but their causative role remains unknown. We did not identify any patients who developed ectasia without recognizable preoperative risk factors.

Objective To study the safety and efficacy of simultaneous bilateral laser in situ keratomileusis (LASIK). Design Prospective randomized clinical trial. Participants Fourteen surgeons and 714 consecutive eyes of 357 patients who desired surgical correction of myopia ranging from −2.00 to −22.50 diopters. Intervention Patients were randomized to simultaneous or sequential bilateral LASIK. Main outcome measures Primary outcome measures were safety and efficacy. Procedure safety was assessed, for simultaneous and sequential groups, by comparison of intraoperative and postoperative complication rates and the percentage of eyes losing two or more lines of spectacle-corrected visual acuity. Procedure efficacy was assessed by comparison of the percentage of eyes with uncorrected visual acuity better than or equal to 20/20 and 20/40 and the percentage of eyes within ±0.50 and ±1.00 diopters of intended outcome. Results Three hundred seventy-eight eyes were enrolled in the simultaneous group, and 331 eyes were enrolled in the sequential group. Mean follow-up was 10 months (±4.2 months standard deviation; range, 2 weeks-22 months). There was no significant difference in intraoperative complication rate ( P = 0.55), loss of two or more lines of spectacle-corrected visual acuity ( P = 0.87), or percentage of eyes within ±0.50 diopters of intended correction ( P = 0.17) between simultaneous and sequential groups. Postoperative complications were not significantly different in the two groups except for the unexplained more frequent epithelial ingrowth in the simultaneous group (2.9%) than in the sequential group (0.6%). The adjusted odds ratio for epithelial ingrowth in the simultaneous group was 1.02 (95% confidence interval, 1.01–1.08). There was no increased likelihood of epithelial ingrowth in the second of two simultaneously treated eyes ( P = 0.95). Conclusion The outcomes and complications of performing bilateral simultaneous LASIK were not significantly different from those of sequential treatments, with the unexplained exception of more frequent epithelial ingrowth in the simultaneous group.

Objective To determine the incidence and severity of complications from laser in situ keratomileusis (LASIK) for the correction of myopia by experienced and inexperienced surgeons. Design Prospective, observational clinical study. Participants Fourteen surgeons and 1062 eyes of 574 myopic patients who desired surgical correction of myopia ranging from −2.00 to −22.50 diopters (D; mean, −7.57 D) and astigmatism no greater than 4.00 D participated in this study. Intervention Myopia was corrected with LASIK. Astigmatism was corrected with arcuate keratotomy at the same time as the initial procedure or subsequently. Main outcome measures Primary outcome measures were change in best spectacle-corrected visual acuity (BSCVA) and the incidence of complications. Results Eyes were followed for a mean of 9.5 months after their last surgical procedure (range, 2 weeks–21 months). Three hundred eighty-one eyes (36%) underwent 468 enhancement procedures 3 months or more after the initial treatment. There were 27 (2.1%) intraoperative and 40 (3.1%) postoperative complications. Laser ablation was not performed during the initial treatment of 17 (1.6%) eyes because of intraoperative complications. Seventy-four eyes gained 2 or more lines of BSCVA, while 50 eyes lost 2 or more lines of BSCVA. Only three eyes lost two or more lines of BSCVA to a level worse than 20/40. One eye with a flap buttonhole (BSCVA 20/50) also had an epiretinal membrane. The second eye (BSCVA 20/60) had a flap buttonhole that may have been related to a previous corneal transplant. The third eye (−22.50 D before surgery) had a rhegmatogenous retinal detachment develop, reducing BSCVA from 20/60 to 20/200. The incidence of intraoperative complications decreased from 3.1% during the first 3 months to 0.7% during the last 9 months of the study ( P = 0.02). Conclusions LASIK is acceptably safe for the correction of myopia. Although complications occur in approximately 5% of cases, these rarely lead to visual loss of more than two Snellen lines and postoperative acuity below 20/40. Flap buttonholes were more likely to cause loss of BSCVA than free or incomplete flaps ( P = 0.02); flap buttonholes may be more likely in eyes that have undergone previous surgery. Complication rates can be reduced as the surgical team gains experience.

Objective This study aimed to determine whether there is a true difference in predictability between single-zone and multizone laser in situ keratomileusis (LASIK) for the correction of low myopia or whether any difference in predictability is because of a need for separate clinical nomograms for the two treatments. Design A prospective, randomized, clinical trial. Participants Fourteen surgeons and 190 eyes of 95 patients with myopia who desired surgical correction of myopia ranging from −2.00 to −7.00 diopters (D) participated. Intervention Fellow eyes of patients with myopia undergoing bilateral simultaneous LASIK were randomized to single-zone and multizone ablation. Astigmatism was not corrected at the time of LASIK. Main outcome measures Predictability, postoperative videokeratography, and contrast sensitivity were assessed at 3 months after surgery. Results At 3 months, r 2 values relating laser setting to change in spherical equivalent refraction were 0.78 for single-zone and 0.76 for multizone ablation; mean outcome with respect to intended was −0.84 D (0.65 standard deviation [SD]) for single-zone and −0.62 D (0.78 SD) for multizone eyes ( P = 0.035). There was no relationship between single-zone and multizone ablation and the likelihood of asymmetric postoperative videokeratography ( P = 0.83). The only difference in contrast sensitivity was a significantly greater decrease in log contrast for multizone eyes at 12 cyc/deg under undilated conditions. Conclusions There is no true difference in predictability between single-zone and multizone LASIK for the correction of low myopia. Separate clinical nomograms for single-zone and multizone LASIK should eliminate the difference in predictability that was observed in this clinical trial.

Objective: The purpose of the study is to determine safety and efficacy outcomes of excimer laser photorefractive keratectomy (PRK) for the treatment of mild-to-moderate myopia. Design: A prospective, multicenter, phase III clinical trial. Participants: A total of 701 eyes of 701 patients were entered in the study; 612 eyes were examined at 2 years after surgery. Intervention: Intervention was photorefractive keratectomy using the Summit ExciMed UV200LA excimer laser (Summit Technology, Inc., Waltham, MA). The treatment zone diameter used was 4.5 mm in 251 eyes (35.8%) and 5 mm in 450 eyes (64.2%). Attempted corrections ranged from 1.50 to 6.00 diopters (D). Main Outcome Measures: Predictability and stability of refraction, uncorrected and spectacle-corrected visual acuity, refractive and keratometric astigmatism, corneal haze, contrast sensitivity, subjective reported problems of glare and halo, and patient satisfaction were the parameters measured. Results: At 2 years, 407 (66.5%) eyes achieved 20/20 or better uncorrected visual acuity and 564 (92.5%) eyes achieved 20/40 or better visual acuity. Three hundred thirty-six (54.9%) eyes were within 0.5 D and 476 (77.8%) eyes were within 1.0 D of attempted correction. Stability of refraction improved with time; 86.8% of eyes were stable within 1.0 D from 6 to 12 months, 94% were stable from 12 to 18 months, and 96.3% were stable from 18 to 24 months. There was no evidence of progressive or late myopic or hyperopic refractive shifts. One hundred fourteen (18.6%) eyes gained 2 or more lines of spectacle-corrected visual acuity, whereas 42 (6.9%) eyes lost 2 or more lines; however, of the latter, 32 (76.2%) had spectacle-corrected visual acuity of 20/25 or better and 39 (92.9%) eyes had 20/40 or better. Four hundred forty-two (72.2%) corneas were clear, 138 (22.5%) showed trace haze, 20 (3.3%) mild haze, 9 (1.5%) moderate haze, and 3 (0.5%) marked haze. On patient questionnaires, 87 (29.7%) patients reported worsening of glare from preoperative baseline; 133 (50.1 %) reported worsening of halo symptoms from baseline. Conclusions: Photorefractive keratectomy appears effective for myopic corrections of −1.50 to −6.00 D. Uncorrected visual acuity is maximized in most eyes by 3 months, although some patients require between 6 months and 1 year to attain their best postoperative uncorrected visual acuity and some may require from 1 to 2 years for stabilization of refraction. Refraction stabilizes progressively without evidence of late myopic or hyperopic refractive shifts. Optical sequelae of glare and halo occur in some patients treated with a 4.5- or 5-mm treatment zone.

Purpose: To identify preoperative and intraoperative characteristics associated with outcomes of photorefractive keratectomy (PRK). Methods: In the phase III multicenter clinical trials of the Summit Technology excimer laser for corrections of 1.5 to 6.0 diopters (D) of myopia, three principal outcomes of PRK on 612 patients were examined: (1) uncorrected visual acuity of 20/40 or better, (2) predictability of refractive outcome within 1.0 D of attempted correction, and (3) stability of refractive result between 12 and 24 months. Multiple logistic regression was used to test for independent associations of multiple preoperative and intraoperative characteristics with each of these outcomes. Results: Older age was independently associated with lesser likelihood of achieving 20/40 or better uncorrected visual acuity (odds ratio=1.08 per incremental year of age, 95% confidence interval [Cl] = 1.04–1.12) and with decreased predictability, specifically with overcorrection (odds ratio=1.09, 95% Cl=1.06–1.12), but age was not associated with stability of refraction. Greater attempted correction was associated independently with a decreased likelihood of 20/40 or better uncorrected visual acuity (odds ratio=2.78 for corrections of 3.5–5.5 D, 95% Cl=1.18–6.75; odds ratio=4.19 for corrections of ≥5.5 D, 95% Cl=1.66–10.58), with decreased predictability (odds ratio=1.72 for corrections of 3.5–5.5 D, 95% Cl=1.05–2.85; odds ratio=2.95 for corrections of ≥5.5 D, 95% Cl=1.65–5.26), and with a reduced likelihood of stability of refraction (odds ratio=3.46 for corrections of ≥5.0 D, 95% Cl=1.32–9.11). No intraoperative characteristics were associated with any of the outcomes assessed. Conclusions: Using this specific excimer laser system with an optical zone of 4.5 or 5.0 mm, patient age and attempted correction are important preoperative characteristics associated with postoperative uncorrected visual acuity and predictability of PRK. Stability of refraction is strongly associated with attempted correction. Such information may help guide patient selection, determine timing of fellow eye treatment, and suggest changes in the laser treatment algorithm for individual patients. Although these findings may be representative of PRK in general, similar analyses should be performed before modifying patient treatments using either a 6.0-mm treatment zone or other laser systems.

• Purpose: We studied the occurrence of late scarring after photorefractive keratectomy and its response to topical corticosteroids and debridement during the course of follow-up of 950 eyes that had photorefractive keratectomy with excimer laser. • Methods: Five eyes of four patients developed localized corneal scars, decreased visual acuity, and increased myopia after five to 33 months of good visual acuity, with trace haze. In two eyes, scars were removed by debridement alone. In these two eyes, recurrent scars were treated by debridement, followed by aggressive treatment with topical corticosteroids. Two other eyes were treated with topical corticosteroids alone. The fifth eye, which developed a scar after debridement to correct a subjective visual distortion after photorefractive keratectomy, was treated with debridement followed by aggressive topical corticosteroids. • Results: Treatment with topical corticosteroids alone in two eyes improved uncorrected visual acuity slightly and decreased myopia, although the scars remained unchanged. Debridement without aggressive topical corticosteroid use resulted in rapid return of the scars and a decrease in visual acuity. Subsequent debridement after aggressive topical corticosteroid treatment resulted in resolution of scars and no recurrence after discontinuation of corticosteroids in one case. In another case, the scar recurred eight months after discontinuation of topical corticosteroids. In Case 4, the scar has not recurred as the topical corticosteroid dosage has been reduced. • Conclusions: Patients who undergo photorefractive keratectomy should be counseled concerning the risk of late scarring, reexamined frequently after photorefractive keratectomy, and treated with topical corticosteroids after corneal trauma. Long-term treatment with topical corticosteroids may be required to prevent the recurrence of scars after debridement.

Many of the deficiencies with human tissue epikeratoplasty might be improved by the use of a suitable synthetic lenticule. Potential biomaterials for epikeratoplasty include collagen (types I1 III, or IV), collagen-hydrogel copolymers, bioactive synthetics, and coated hydrogels. The biomaterial must be engineered to achieve strict specifications of optical clarity, support of epithelial migration and adhesion, permeability to solutes, and stability to corneal proteases. Attaching synthetic lenticules to the cornea without cutting Bowman's layer by adhesives, laser welding, or direct adhesion may also improve the efficacy of synthetic epikeratoplasty. Refract Corneal Surg 1991;7:240-248.)

We used a milliwatt continuous wave CO2 laser mounted on an operating microscope to study the feasibility of welding synthetic collagen epikeratoplasty lenticules to the cornea. In vitro studies and experimentation in rabbits and monkeys showed no welding effects using direct laser radiation with powers ranging from 17 mW to 1 W. Only tissue shrinkage was observed. Experiments using various adjunctive solders produced a temporary welding effect using 30% bovine serum albumin welded with a power of 35-45 mW, 325 urn spot size, moving the beam 5 mm/sec. The lenticules remained in place until the 4th postoperative day when epithelium grew underneath the lenticule, dislodging it. Histopathologic examination demonstrated epithelial migration over the solder displacing the epikeratoplasty lenticule and anterior stromal denaturization and disruption. [Refract /ve and Cornea/ Surgery 1990;6:430-436.]

Excimer laser keratomileusis (photorefractive keratectomy, direct corneal ablation) for myopic corrections of 2.00 diopters (n = 1), 4.00 D (n = 4), and 8.00 D (n = 3) was performed on eight corneas of four Rhesus monkeys. All animals were followed for 18 months. The ablations healed normally and no epithelial erosions occurred. Serial slit-lamp microscope examinations revealed that a variable amount of corneal haze developed in all animals; this haze progressively faded during the follow-up period. Histopathology revealed an epithelium of normal thickness, basement membrane abnormalities, increased number and activity of stromal keratocytes, and a variable amount of newly secreted extracellular matrix in the anterior stroma. These findings suggest that excimer laser keratomileusis induces a mild wound healing response in the anterior cornea which displays considerable individual variability and persists up to 18 months. [Refractive and Corneal Surgery 1990;6:340-345.]

Purpose: To report the incidence and outcomes of diffuse lamellar keratitis (DLK) after LASIK and to analyze potential causative factors. Methods: Retrospective review of 15,119 cases (11,232 primary procedures and 3887 enhancements) from 7168 patients undergoing LASIK from May 1995 through October 2002, comparing preoperative data and postoperative outcomes for each case developing DLK to patients in the study population and a control series of eyes that did not develop DLK. Results: We identified 61 eyes (0.40%) that developed DLK after LASIK. Three study groups were identified based on sterilization protocols used: (1) steam autoclave without reservoir (8348 cases), (2) cassette autoclave with reservoir (6771 cases), (3) steam autoclave without reservoir and new instrument cleaner (1758 cases). Significantly more eyes developed DLK with Protocol 2 (47 cases, 0.94%) than with Protocol 1(11 cases; 0.1%; P < 0.0001) or Protocol 3 (3 cases, 0.2%; P < 0.0005). There was no significant difference in the incidence of DLK in Protocol 1 versus Protocol 3. DLK was significantly more common after primary procedures than with enhancement procedures only under Protocol 2. No individual developed DLK after more than 1 procedure. Treatment protocols included frequent topical steroids only (24 cases, 39.3%), frequent topical steroids and oral steroids (19 cases, 31.2%), or topical and oral steroids combined with lifting and irrigating beneath the flap (18 cases, 29.5%). Final refractions and visual acuities were not significantly different in eyes that developed DLK and those that did not. Conclusions: DLK is a nonspecific inflammatory response to multiple stimuli that cannot be attributed solely to individual variation in the inflammatory response, the microkeratome, or material deposited by the microkeratome. Sterilizers with reservoirs may cause some cases of DLK. With appropriate diagnosis and treatment, DLK should resolve without sequelae, yielding visual outcomes comparable to cases with uneventful postoperative courses.

To compare visual outcomes in eyes undergoing aberrometry-guided (InterWave) LASIK with those in eyes undergoing standard LASIK treatment based upon refractive measures.Single-center, comparative, interventional, consecutive case series.Four hundred two consecutive eyes undergoing LASIK were analyzed retrospectively. One group, 106 eyes undergoing primary LASIK and 224 eyes undergoing LASIK enhancement, was treated with standard LASIK treatment using a 5.5-mm optical zone, 1.5-mm transition zone laser with the settings determined by manifest refraction. The second group, 44 untreated (primary) eyes and 28 previously treated (enhancement) eyes, received a multipass, multistage treatment in which the laser settings for each stage were determined by aberrometry measurements. Eyes with desired monovision (undercorrected) outcome and preoperative hyperopia were excluded from the study.An aberrometry-guided laser treatment (InterWave LASIK) was compared with the standard LASIK treatment based upon the manifest refraction.Uncorrected visual acuity (VA), manifest refraction, best spectacle-corrected VA (BSCVA), severity of halos, and root mean square (RMS) retinal blur area measured at 3 months postoperatively.Three months postoperatively there was no difference in uncorrected VA, BSCVA, refraction, or RMS retinal blur areas for pupil sizes of 3.5 mm between eyes treated by InterWave and those treated by standard LASIK. However, InterWave LASIK reduced the retinal blur area by 48% (P0.0103) and 58% (P0.0004) in primary cases and 43% (P0.0430) and 74% (P0.0271) in enhancement cases, respectively, for pupil sizes of 4.5 and 6.5 mm relative to standard LASIK treatments. Patients undergoing InterWave-guided treatment reported less severity of halo (0.37 vs. 0.98 [P0.016] for primary cases and 0.35 vs. 0.73 [P0.04] for enhancement cases).InterWave LASIK achieved acuity and refractive results equivalent to those of standard LASIK treatment based upon refraction, but resulted in superior quality mesopic vision.

Objective The purpose of this study was to define qualitative patterns of videokeratography after excimer laser in situ keratomileusis (LASIK) for myopia and to identify associations of videokeratography patterns with clinical variables. Design Single-center, retrospective, cohort study. Participants One hundred twenty-six eyes of 68 patients with myopia who desired surgical correction of myopia ranging from −1.50 to −8.80 diopters. Intervention Myopia was corrected with LASIK using a Summit OmniMed/Apex excimer laser. Computer-assisted videokeratography data were acquired at 3 months after primary LASIK, and associations of videokeratography pattern with clinical variable were assessed. Main outcome measures Seven subgroup ablation zone patterns were characterized using tangential curvature maps; these subgroups were combined into pooled symmetric and asymmetric groups. Associations with age, attempted correction, single-zone or multizone ablation, postoperative uncorrected and spectacle-corrected visual acuity, predictability, astigmatism, corneal uniformity, glare disability, and contrast sensitivity were analyzed. Results Thirty-two eyes (25.4%) showed a uniform pattern, 14 eyes (11.1%) showed a bow-tie pattern, 22 eyes (17.5%) showed a peninsula pattern, 22 eyes (17.5%) showed a semicircular pattern, 22 eyes (17.5%) showed an off-center blue spot pattern, 10 eyes (7.9%) showed an irregular pattern, and 4 eyes (3.2%) showed a central island pattern. Spectacle-corrected visual acuity, astigmatism, corneal uniformity, glare disability, and contrast sensitivity were significantly related to videokeratography pattern, although the difference among videokeratography groups was clinically small. Age, attempted correction, single- or multizone ablation, and postoperative uncorrected visual acuity and predictability were not predictive of videokeratography pattern. Conclusions Most eyes in this study had an asymmetric videokeratography pattern 3 months after LASIK. Small but statistically significant differences were identified among the videokeratography patterns that potentially may affect postoperative quality of vision.

Purpose To assess the effects of laser in situ keratomileusis (LASIK) on the corneal endothelium. Methods In a prospective study, the corneal endothelium of 98 eyes of 65 consecutive patients (mean age, 41 years; range, 22 to 66 years) was photographed before, 2 weeks after, and 12 weeks after LASIK for the correction of 2.75 to 14.5 diopters of myopia. Theoretical ablation depths were 200 to 330 μm below the corneal surface. Cell density, coefficient of variation, and percent of hexagonal cells were determined using 150 to 200 cells from each image. Eighty-eight eyes (91%) of 59 patients had a history of contact lens wear. Results The mean ± SD preoperative endothelial cell density was 2,549 ± 365 cells per mm 2 , and the mean coefficient of variation was 0.35 ± 0.06. There was no statistically significant change in the mean endothelial cell density or mean coefficient of variation of cell size at the 2-week (2,561 ± 360 cells per mm 2 and 0.35 ± 0.06) or 12-week (2,541 ± 364 cells per mm 2 and 0.35 ± 0.05) postoperative examinations. The percent of hexagonal cells was not significantly changed 2 weeks postoperatively; however, 12 weeks postoperatively ( P =.0413, two-tailed t test), the percent of hexagonal cells was decreased by 1%. Conclusions Corneal endothelial cell density and morphology were unchanged 2 and 12 weeks after LASIK for the correction of up to 14.5 diopters of myopia. In this LASIK study, the correction of up to 14.5 diopters of myopia appears to cause no clinically significant effect on corneal endothelial cell density or morphology.

Purpose: ^The authors prospectively investigated the effect of excimer laser photorefractive keratectomy (PRK) for myopia on the corneal endothelium. Methods: Quantitative computer-assisted morphometric analysis of central and peripheral corneal endothelial cells was performed on 142 myopic eyes before and at 3 months, 1 year, and 2 years after PRK. The mean age of the subjects was 37 years (range, 21-66 years). Ninety-one (64%) of them had a history of contact lens wear. Mean attempted correction was -3.9 diopters (range, -1.6 to -6.0 diopters). Results: The mean preoperative endothelial cell density was 2660 cells/mm2 centrally and 2776 cells/mm2 peripherally. There was no change in central endothelial cell density at any of the postoperative examinations. The peripheral cell density decreased 4.1 % ( P = 0.003) at 3 months and 6.2% ( P = 0.0001) at 1 year. However, the peripheral cell density was not significantly different from the preoperative value at 2 years. The peripheral coefficient of variation of cell size was 7.8% lower 2 years postoperatively than it was preoperatively, and this improvement was attributable to cessation of contact lens wear after PRK. The decrease in peripheral endothelial cell density at 1 year correlated with the amount of attempted correction, but there was no correlation between attempted correction and the change in central or peripheral endothelial cell density 2 years postoperatively. Conclusion: For the correction of up to 6.0 D of myopia, PRK causes no detectable changes in central corneal endothelial cell density, but it does cause a transient, modest loss of peripheral corneal endothelial cells at 1 year. Variations in endothelial cell shape caused by contact lens wear resolve after PRK.

We report six-month results of the Summit Technology Myopic Keratomileusis Phase I multicenter study. Fifty-seven eyes of 57 patients had keratomileusis to correct high myopia. A microkeratome was used for the primary keratectomy and the excimer laser was used to ablate the stroma of the resected lenticle (cap) or the stromal bed (in situ). At six months, 31 of the 47 eyes available for follow-up (65.9%) had uncorrected visual acuity of 20/40 or better; 16 (34.0%) had uncorrected acuity of 20/25 or better. Thirty-seven eyes (78.7%) maintained the same (± one Snellen line) best corrected visual acuity as before surgery; seven (14.9%) lost two lines and three (6.4%) lost more than two lines. In addition to the six-month multicenter study results, we report two year results in a subset of 28 eyes (22 from the multicenter study and six fellow eyes). At six months, 17 of the 24 eyes available for follow-up (70.9%) had uncorrected visual acuity of 20/40 or better and nine (37.5%) had uncorrected acuity of 20/25 or better, including eyes that had worse than 20/80 best corrected visual acuity preoperatively. At 24 months, five of the seven eyes available for follow-up (71.4%) had uncorrected acuity of 20/25 or better. Only one patient lost two lines of best corrected vision at six months and no patient lost more than two lines; at 24 months, all patients maintained (± one line) best corrected vision. Our findings suggest that myopic keratomileusis performed with the microkeratome, using the excimer laser for the refractive cut, is a safe, effective, and relatively predictable way to correct high myopia in the 6.0 to 25.0 diopter range. With longer follow-up, the accuracy of the refractive correction, as well as best corrected visual acuity and uncorrected visual acuity, continues to improve.

We examined 15 eyes of ten patients with complications of hexagonal keratotomy, which included glare, photophobia, polyopia, fluctuation in vision, overcorrection, irregular astigmatism, corneal edema, corneal perforation, bacterial keratitis, cataract, and endophthalmitis. Wound healing abnormalities and anterior displacement of the central cornea adjacent to the incisions were common. Eight eyes lost best-corrected visual acuity of two or more Snellen lines. Three eyes required penetrating keratoplasty for visual rehabilitation. Histologic analysis of two of these corneas disclosed variations in wound depth and abnormalities of wound configuration, including considerable wound gaping. Hexagonal keratotomy appears to be an unpredictable, unsafe surgical procedure with a high complication rate, and it should be abandoned until well-controlled experimental trials establish its safety and efficacy.

Human type IV collagen discs were found to support proliferation and adhesion of rabbit corneal epithelial cells in tissue culture. To assess the biocompatibility of this synthetic collagen for epikeratoplasty, seven eyes of seven rhesus monkeys underwent epikeratoplasty with lenticules made of human type IV collagen. Eye rubbing by the animals expulsed two of the lenticules and caused failure of two to epithelialize completely. The remaining three lenticules epithelialized, remained clear, and caused no adverse effects on the eye. Two of these lenticules developed focal areas of subepithelial thinning 3 months postoperatively and the third lenticule has remained stable for 30 months. The presence of epithelial attachment components at the epithelial-lenticule interface was demonstrated by immunolocalization. Histopathologic and ultrastructural examination revealed focal areas of epithelial invasion and degradation of the lenticule. Neutral proteases were detected in the thinning region of one specimen. Human type IV collagen supports epithelialization in vivo and may have potential as a biomaterial for epikeratoplasty, but the stability of the material must be improved.

Excimer laser photorefractive keratectomy (PRK) is presently under investigation for the correction of myopia. Two companies in the United States, Summit Technology (Waltham, Mass.) and VisX, Inc. (Sunnyvale, Calif.) have developed excimer laser delivery systems and are participating in an FDA study to determine the safety and efficacy of PRK. This is a preliminary report on the refractive and visual results of 51 of 100 eyes treated between October 10, 1990 and March 7, 1991 by the Summit Technology UV200LA excimer laser under the FDA Phase IIB FDA protocol one year after surgery. More detailed information on eight patients treated at Emory University Eye Center (Emory Subgroup) is also reported.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Photorefractive keratectomy (PRK) using an argon fluoride excimer laser for photoablation of the cornea shows potential for the precise correction of refractive errors in patients. Usually, the epithelium is mechanically removed, and Bowman's layer and stromal tissue are photoablated to precomputed depths and shapes that are based on known ablation rates for these tissues. After four day's time, the epithelium has regrown. Assuming the epithelium to be preoperatively uniform in thickness across the central optical zone, and assuming that it regrows to the same thickness, a theoretical precision of +/- 0.05 diopters is achievable with PRK. Keratometric measurements of the epithelium and of Bowman's layer were made at the 2.0 and 3.6 mm optical zones on 10 fresh cadaver eyes (

The authors demonstrate the use of a frequency multiplied Q-switched Nd:YAG laser to generate the fifth (213 nm) and the fourth (266 nm) harmonic frequencies to ablate porcine corneas and synthetic collagen materials. This new strategy is discussed for corneal refractive surgery using a solid state laser. The potential for spatially resolved refractive correction based on a 213 nm solid state laser is reviewed in light of new corneal imaging technology that can detect localized refractive errors of the eye. Finally, the authors discuss remaining problems that need to be addressed before this technology can be applied to clinical investigation.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We used a Q-switched Nd:YAG laser with non-linear optical crystals to produce the 5th (213 nm) and the 4th (266 nm) harmonic frequencies. Using these two wavelengths, we ablated fresh porcine corneas and type I collagen synthetic epikeratoplasty lenticules. For the 213-nm ablation, radiant exposure was 1.3 J/cm2. The ablation rate was 0.23 micron per pulse for the epikeratoplasty lenticules. We examined all tissues with light microscopy, transmission electron microscopy, and scanning electron microscopy. Histology for the 213-nm ablation showed a clean ablation crater with minimal collagen lamellae disruption and a damage zone less than 1 micron. In comparison, the 266 nm radiation showed more charring at the edges with a damage zone approximately 25 microns deep with disruption of the stromal lamella. Our results show that this solid state UV laser is a potential alternative to the excimer laser for cornea surgery.

The healing response of the cornea following excimer laser anterior keratomileusis (a 4-mm-diameter ablation to a depth of 11, 23, or 46 microns) was analyzed immunohistochemically in adult rhesus monkeys. The ablated surface had reepithelialized and the synthesis of type VII collagen (a major component of anchoring fibrils) was evident by 7 days; the reestablishment of a nearly continuous anchoring fibril zone was evident after 12 weeks. Stromal fibroblasts, activated in response to wounding, expressed a fetal antigen for approximately 6 weeks. Although fibronectin and type VII collagen were present only transiently in the regenerating subepithelial stromal matrix in the subepithelial regions, some other alterations, including the presence of type III collagen, increased levels of keratan sulfates, and discontinuities in the anchoring fibril zone were evident even 18 months after wounding. The depths of the regenerated stroma, which were estimated from the depths of remnant staining for type VII collagen in the stromal matrix, generally, but not always, corresponded to the depths of the calculated ablation.

Laser myopic keratomileusis (photorefractive keratectomy) was performed on 29 rhesus monkey corneas with an argon fluoride (193-nm) excimer laser and a computer-controlled, moving slit delivery system. The 4-mm-diameter central ablation zone ranged in depth from 11 microns (-2 diopters effect) to 46 microns (-8 diopters effect). Corneas were studied for the 9 months postoperatively by clinical slit-lamp microscopy, and periodically with light and transmission electron microscopy. By 6 weeks, mild to moderate subepithelial haze was apparent in 93% of the corneas, with considerable variability in density. Progressive clearing occurred so that by 6 to 9 months 12 of 13 surviving corneas (92%) were either completely clear (4 corneas) or trace hazy (8 corneas). The epithelium was thickened at 21 days after ablation and returned to normal thickness by 3 months. At 3 weeks, subepithelial fibroblasts were three times the density of normal keratocytes and returned to nearly normal numbers by 9 months. We concluded that the anterior monkey cornea demonstrated a mild, typical wound healing response after excimer laser keratomileusis.

Objective To examine the histologic and ultrastructural features of human corneas after successful laser in situ keratomileusis (LASIK) in 2 patients post mortem. Methods Portions of 4 corneas were processed for histology, transmission electron microscopy, and scanning electron microscopy. Results Case 1 had undergone LASIK 3 months prior to death and case 2 had undergone LASIK 20 months prior to death. A Hansatome (Bausch & Lomb Surgical Inc, Clarement, Calif) microkeratome with a 180-µm plate had been used for case 1 and an Automated Corneal Shaper (Chiron Corporation, Munich, Germany) with a 160-µm plate had been used for case 2. Histologically, the LASIK flap measured 160 µm and 150 µm in thickness in case 1 and case 2, respectively. Corneas from both cases exhibited minor epithelial ingrowth into the wound, reactive keratocytes at the wound margin, irregular collagen fibrils in the wound bed, and severed collagen bundles at the flap hinge. These findings were more pronounced in case 1 than in case 2, and the wound interface was virtually imperceptible in case 2. Additionally, the corneas from case 1 contained periodic acid-Schiff–positive electron dense material and wide-spaced collagen at the wound interface, and there was an absence of corneal nerves. Conclusions These findings show that changes caused by wound repair that are present at 3 months are minor 20 months after LASIK.

Objectives To study the effects of radial keratotomy (RK) and photorefractive keratectomy (PRK) on contrast sensitivity and glare disability using 4 different devices, and to correlate subjective complaints with objective scores of visual performance. Methods Preoperative contrast sensitivity for 30 eyes undergoing RK and 30 eyes undergoing PRK was compared with contrast sensitivity at 1, 3, and 6 months postoperatively using the CSV 1000, MCT (Multivision Contrast Tester) 8000, and Pelli-Robson chart. The BAT (Brightness Acuity Tester) and MCT 8000 were used to test for daytime and nighttime glare disability, respectively. At 3 and 6 months postoperatively, a questionnaire was administered to assess visual performance subjectively. Results Contrast sensitivity decreased after RK and PRK up to the sixth postoperative month, while glare disability was significantly increased at 1 month after PRK as determined by the MCT 8000 and the BAT, and at the third and sixth months after RK using the MCT 8000. Compared with RK, PRK significantly decreased contrast sensitivity as measured with the MCT 8000 at all spatial frequencies 1 month postoperatively. No significant difference in visual performance between patients undergoing RK and PRK was observed with the CSV 1000, the Pelli-Robson chart, or the BAT up to 6 months postoperatively. No consistent difference was found between glare disability scores of patients undergoing RK and PRK when measured with the MCT 8000. Subjective reports of problems with night driving and blurring correlated only with glare disability scores of the MCT 80003 months after RK. Conclusions Both RK and PRK reduce contrast sensitivity and cause glare disability; however, the relative effect is highly dependent on the time postoperative testing is performed and the instrument used for testing. Contrast sensitivity and glare disability, as measured by the instruments used in this study, do not accurately reflect patients' subjective assessment of visual performance in daily life.

• Five rhesus monkey eyes underwent repeated argon fluoride (193 nm) excimer laser myopic photorefractive keratectomy 3 months following an initial ablation that had produced mild subepithelial haze. At 3 months all eyes had development of a dense subepithelial opacity and a thickened epithelium (12 cells, 80 μm) with vacuolization of basal cells, fragmented basement membrane, and a layer of subepithelial fibrosis containing activated fibroblasts. By 6 months the opacity was clearing; epithelium was thinner (50 μm); subepithelial fibrosis was more lamellar. By 15 months only mild haze persisted clinically; epithelium was 30 μm thick, with persistent basal vacuolization and focal basement membrane disruption; subepithelial fibrous tissue was more organized. Early repeated excimer laser ablation of the monkey cornea apparently induces vigorous stromal wound healing. Use of shallower ablations, corticosteroids, or a longer delay between ablations may be necessary for repeated laser surgery to be practical clinically.

Local wavefront distortion by the total refractive system of the eye is measured by a variant of the Scheiner principle at some thirty loci of 1 mm diameter. At each locus we find the normal to the wavefront that could form a point focus. A simple visual display is used to review the data, and a steepest descents fit of the wavefronts with a power series enables comparison with more traditional measures of refractive error.

In response to concerns regarding possible DNA damage by far ultraviolet radiation during excimer laser corneal surgery, the mutagenic potential of an argon fluoride excimer laser (193 nm) on BALB/3T3 mouse fibroblasts grown in tissue culture was investigated. The cumulative incidence of anaplastic transformation after subablative radiant exposures from 3.5 mJ/cm2/pulse to 13.4 mJ/cm2/pulse was 3.6% of all cell cultures. The incidence of anaplastic transformation in nonirradiated controls was 4.2%. Transformation after exposure to x-ray radiation (60.9 rad) was 98.8%. The difference between the incidence of transformation of nonirradiated controls or excimer-treated cultures compared with x-ray radiation-treated cells was significant P less than 0.0001 (chi square test). In this standard cell line, 193-nm laser energy does not appear to have substantial mutagenic potential.

To the Editor. —The 193-nm wavelength generated by the argon fluoride excimer laser precisely ablates corneal tissue without evidence of adjacent thermal damage.1Lower-energy excimer wavelengths, including 248, 308, and 351 nm, have been investigated and found to produce a zone of adjacent thermal damage that increases with the wavelength. The mechanism by which far ultraviolet (UV) energy interacts with corneal tissue is controversial and poorly understood. Srinivasan and colleagues2have suggested that highly energetic far UV photons (6.4 eV at 193 nm) directly break the intramolecular bonds that link the collagen polymer together. This process is dependent on high corneal absorption of the wavelength and sufficient photon energy to induce bond disruption.2Other possible mechanisms include ultrafast thermal events in which heating is confined to a small volume of corneal tissue that is vaporized before significant thermal diffusion into surrounding cornea occurs. We irradiated human cadaver corneas