Keratolysis following excimer laser phototherapeutic keratectomy in a patient with keratoconus.

PURPOSE: We report a case of keratolysis following phototherapeutic keratectomy (PTK) for a subepithelial nodule in a patient with keratoconus. METHODS: A 29-year-old male with keratoconus who became contact lens intolerant because of a raised subepithelial nodule was treated with excimer laser phototherapeutic keratectomy (PTK). RESULTS: The epithelium failed to heal postoperatively, and progressive keratolysis led to a central descemetocele by the eighth postoperative day. The patient was managed with a penetrating keratoplasty. CONCLUSIONS: Excimer laser phototherapeutic keratectomy has been shown to be an effective treatment for subepithelial nodules in patients with keratoconus. Rapidly progressive keratolysis is a potential complication of this procedure.

Laser in situ keratomileusis: surgical technique.

Laser in-situ keratomileusis is an increasingly popular technique for the correction of refractive errors that was initially described by Pallikaris in 1990. It involves the excimer laser ablation of corneal stroma beneath a hinged corneal flap that is created with a microkeratome. The purpose of this chapter is to report the LASIK surgical technique that has evolved at the Emory Vision Correction Center since 1995 when an investigation study of this technique for the correction of myopia began.

Laser in situ keratomileusis for myopia up to -11 diopters with up to -5 diopters of astigmatism with the summit autonomous LADARVision excimer laser system.

OBJECTIVE: To assess the safety and effectiveness of the Summit Autonomous LADARVision active tracking narrow beam excimer laser system for laser in situ keratomileusis (LASIK) correction of myopia and astigmatism. DESIGN: A multicenter, prospective noncomparative case series. PARTICIPANTS: This cohort consisted of 177 eyes corrected for spherical myopia up to -11 diopters (D) and 170 eyes corrected for myopia up to -11 D spherical equivalent with astigmatism up to -5 D. INTERVENTION: Treatments were performed at four sites in the United States using a 6-mm optic zone for spherical myopes and a 5.5-mm optic zone with a 1-mm blend for astigmats. MAIN OUTCOME MEASURES: Visual acuity, subjective refraction, vector analysis, subject satisfaction, intraocular pressure, complications, and adverse reactions. RESULTS: Six-month follow-up was available on 157 spherical eyes and 113 astigmatic eyes. For spherical myopes, uncorrected visual acuity (UCVA) was 20/20 or better in 60.5%, 20/25 or better in 80.3%, and 20/40 or better in 93.9%. The mean spherical equivalent was -0.29 +/- 0.45 D with 75.2% +/- 0.50 D and 94.9% +/- 1.00 D of intended. A loss of two lines of best spectacle-corrected visual acuity (BSCVA) occurred in 0.6%, and no eyes lost greater than two lines of BSCVA. For astigmatic myopes, UCVA was 20/20 or better in 52.0%, 20/25 or better in 74.5%, and 20/40 or better in 94.1%. The mean spherical equivalent was -0.23 +/- 0.49 D with 75.2% +/- 0.50 D and 95.6% +/- 1.00 D of intended. A loss of two lines of BSCVA occurred in 0.9%, and no eyes lost greater than two lines of BSCVA. Vector analysis showed that 99% of the intended cylinder was corrected on average with a mean angle of error of 4.2 degrees. Refractive stability was achieved between 1 and 3 months in 97.5% of spherical eyes and 99.4% of astigmatic eyes and confirmed between 3 and 6 months in 100% of both spherical and astigmatic eyes. CONCLUSIONS: Eyes treated for myopia up to -11 D of spherical equivalent with or without astigmatism up to -5 D show early refractive stability, good UCVA outcomes, no significant loss of BSCVA, accurate correction of astigmatism, and slight undercorrection without a change from the photorefractive keratectomy algorithm and with a single treatment.

Effects of laser in situ keratomileusis (LASIK) on the corneal endothelium 3 years postoperatively.

PURPOSE: To investigate the effects of laser in situ keratomileusis (LASIK) on the corneal endothelium 3 years postoperatively. METHODS: Patients who were subjects of a previous prospective study (Am J Ophthalmol 125:465-471, (April) 1998) were contacted for a follow-up analysis of the central corneal endothelium. Noncontact specular microscopy was performed 35 to 37 months after LASIK on 52 eyes of 27 patients of the original cohort of 98 eyes of 65 patients and six eyes of three patients who were previously lost to follow-up after their initial post-LASIK evaluation. Patient age ranged from 29 to 66 years at the time of the original LASIK procedure. Attempted corrections ranged from 2.25 to 14.5 diopters of myopia, giving theoretical ablation depths of 182 to 332 microm below the corneal surface. Forty-eight eyes (83%) had a history of preoperative contact lens use (3 to 33 years). Central endothelial cell density, coefficient of variation of cell size, and percent of hexagonal cells were analyzed using 72 to 152 cells from each image. Multivariate analysis was used to search for factors that might predict changes in cell density, coefficient of variation, and percent of hexagonal cells. RESULTS: The mean +/- SD preoperative cell density was 2,498 +/- 354 cells per mm(2), the mean coefficient of variation was 0.36 +/- 0.07, and the percent of hexagonal cells was 58 +/- 6. Three years after surgery there was no statistically significant change in the mean endothelial cell density (2,489 +/- 335 cells per mm(2); P = 0.88, paired t test) or the percent of hexagonal cells (60 +/- 7; P = 0.14, paired t test). The mean coefficient of variation was significantly lower postoperatively (0.32 +/- 0.04; P = 0.0006, paired t test); a repeated measures analysis showed that this significant improvement could not be explained by cessation of contact lens wear after LASIK (P = 0.34). Multivariate analysis did not identify any factors that were predictive of change in cell density, coefficient of variation, and percent of hexagonal cells. CONCLUSIONS: Laser in situ keratomileusis for the correction of 2.25 to 14.5 diopters of myopia had no significant effect on central corneal endothelial cell density or the percent of hexagonal cells 3 years after surgery. The coefficient of variation of cell size improved significantly 3 years after surgery.

Monocular diplopia related to asymmetric corneal topography after laser in situ keratomileusis.

PURPOSE: To show a specific relationship between monocular diplopia and corneal refractive asymmetry after laser in situ keratomileusis (LASIK). METHODS: One hundred thirty-eight eyes of 98 patients who underwent LASIK for myopia between -2.12 and -17.75 D were examined under room-lighted conditions. We examined 51 eyes at 2 weeks, 46 eyes at 3 months, 32 eyes at 6 months, and 9 eyes at 1 year after LASIK. We attempted to correlate the presence of monocular diplopia with their corneal topographical features. RESULTS: Eight eyes of five patients (five eyes at 2 weeks, three eyes at 3 months after LASIK) produced symptoms of monocular diplopia. These symptomatic patients had a common corneal topographical feature caused by decentralized or inhomogeneous ablation. Every pupillary area in the patients' topographies contained steeper and flatter areas. The range of refractive power variation in these asymmetric areas was at least 1.50 D. The location of the secondary image correlated with the direction of the steeper area in all eight eyes. Pinhole viewing eliminated or reduced the prominence of secondary images in every case. CONCLUSION: Monocular diplopia following LASIK appears to correlate with postoperative corneal refractive power variation inside the pupillary area, caused by decentralized or inhomogeneous ablation.

Advances in refractive surgery: 1975 to the present.

PURPOSE: To review the major advances in the field of refractive surgery occurring over the past 25 years. METHODS: Literature review. RESULTS: The major developments in refractive surgery over the past 25 years are reviewed. CONCLUSIONS: The past 25 years have witnessed great changes in refractive surgery. As a result of advancements in technology, instrumentation, and technique, we have seen improvements in the treatment of all types of ametropias. In this article, we review some of the successes and failures of the past quarter-century.

Videokeratography after excimer laser in situ keratomileusis for myopia.

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.

Multiple regression and vector analyses of laser in situ keratomileusis for myopia and astigmatism.

PURPOSE: To construct a quantitative model relating refractive results to laser settings and other factors. METHODS: A prospective clinical trial was performed, including 14 surgeons and 523 eyes of 278 patients who desired correction of myopia from -1.00 to -16.00 D (mean, -6.20 D) and astigmatism up to 6.00 D (mean, 1.10 D). Myopia and astigmatism were corrected by laser in situ keratomileusis (LASIK) with sequential spherical and cylindrical ablations using a 5.5-mm ablation zone and a transition zone to 7.0 mm. The Nidek EC-5000 excimer laser and the Chiron Automated Corneal Shaper were used. RESULTS: Surgically induced refractive changes 3 months after surgery were measured. Spherical ablation by LASIK produced a 19% greater refractive change than that predicted by the Nidek PRK algorithm. The laser setting needed to achieve each 1.00 D of cylinder correction induced 1.30 D change in spherical equivalent refraction (0.80 D more than expected). Patient age and nonlinear effects had small but statistically significant influences on refractive outcome. Sex, left/right eye, and surgeon were not significant factors. Residual variations in spherical equivalent refraction included a 0.50-D constant plus 9% of the predicted spherical equivlanet change. Residual variations in the parallel and orthogonal components of cylinder correction were, respectively, 28% and 13% of the predicted cylinder change plus a 0.30-D constant component. The standard deviation of axis alignment error for cylinder ablation was 3.7 degrees. CONCLUSIONS: Cylindrical ablation produced a spherical change that was larger than expected. To compensate for this, spherical ablation should be reduced in eyes with astigmatism. Variability in the correction of astigmatism was proportionally larger than that for spherical correction and was primarily due to magnitude rather than axis error.

Prospective randomized comparison of simultaneous and sequential bilateral laser in situ keratomileusis for the correction of myopia.

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.

Long-term results of corneal graft survival in infants and children with peters anomaly.

OBJECTIVE: To determine the long-term results of corneal graft survival after penetrating keratoplasty for Peters anomaly and to identify risk factors for graft failure. DESIGN: Noncontrolled interventional case series: a single-center retrospective review of a consecutive surgical series. PARTICIPANTS: The records of all children 12 years of age or younger who underwent penetrating keratoplasty for Peters anomaly between January 1971 and December 1992 were reviewed. All study eyes had completed a minimum of 3 years of follow-up from the date of first keratoplasty and had undergone most of their corneal surgery at Emory University. INTERVENTION: Characteristics of the recipient, the eye, the donor, and the surgical procedure were analyzed for their influence on survival of the first graft. Survival probabilities were estimated using the Kaplan-Meier method. Multivariate regression analysis was performed to estimate relative risks and adjusted survival probabilities. MAIN OUTCOME MEASURE: Graft clarity. RESULTS: One hundred forty-four penetrating keratoplasties were performed in 72 eyes of 47 patients. The median age at first keratoplasty was 4.4 months. The median follow-up was 11.1 years. Fifty-four percent of eyes received one graft, 18% received two grafts, and 28% received three or more grafts. The overall probability of maintaining a clear first graft was 56% at 6 months, 49% at 12 months, 44% at 3 years, and 35% at 10 years. The probability of second or subsequent grafts surviving for 3 years was less than 10%. Thirty-nine percent of eyes had a clear graft at the time of review; 36% of eyes had a clear first graft. Multivariate analysis identified disease severity, donor cornea size, coexisting central nervous system abnormalities, and quadrants of anterior synechiae as the strongest risk factors for graft failure. Supplemental multivariate analysis, restricted to observable preoperative variables, identified stromal vessels, total limbal opacification, and preoperative glaucoma as independent preoperative predictors of graft failure. Allograft rejection was the most frequently identified cause of graft failure. Major complications after keratoplasty were phthisis, retinal detachment, cataract, and glaucoma. CONCLUSIONS: The overall long-term probability of maintaining a clear graft after initial penetrating keratoplasty for Peters anomaly is 35% +/- 0.06%, with subsequent grafts rarely surviving. Eyes with severe disease, larger donor corneas, coexisting central nervous system abnormalities, and anterior synechiae have significantly poorer outcomes than eyes without these factors. These data should be carefully considered before recommending corneal transplantation for Peters anomaly, particularly after previous graft failure.

Complications of laser in situ keratomileusis for the correction of myopia.

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.

[Hereditary benign intraepithelial dyskeratosis]. / Hereditäre benigne intraepitheliale Dyskeratose.

BACKGROUND: Hereditary benign intraepithelial dyskeratosis (HBID) is a rare autosomal dominant disorder with incomplete penetrance. It is characterized by bilateral limbal conjunctival plaques combined with similar changes in the oral mucosa. PATIENT: An 11-year-old African-American patient presented with bilateral chronic conjunctivitis, nasal and temporal limbal conjunctival plaques, and plaques of the oral mucosa, all of which resisted therapy. The onset of the symptoms was in early childhood. Conjunctival smears, allergy tests, blood samples and the internal examination were inconclusive. Histologically, the ocular lesions showed acanthosis, parakeratosis, hyperkeratosis and dyskeratosis. An infiltrate of chronic inflammatory cells was present beneath the intact epithelial basement membrane. CONCLUSIONS: The clinical and histological findings are characteristic of HBID. Symptoms usually start in early childhood and show a waxing and waning course. HBID was first seen among Haliwa Indians in North Carolina. In the meantime HBID has been described in other parts of the US and also in Europe. As these patients were not related to any of the Haliwa Indians, they are considered new mutations. Malignant changes of the conjunctival or oral lesions have not been reported.

Prospective comparison of single-zone and multizone laser in situ keratomileusis for the correction of low myopia.

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, r2 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.

Effects of laser in situ keratomileusis (LASIK) on the corneal endothelium.

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 microm 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 mm2, 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 mm2 and 0.35+/-0.06) or 12-week (2,541+/-364 cells per mm2 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.

Keratocyte repopulation in epikeratoplasty specimens.

PURPOSE: To study the histology and pattern of keratocyte repopulation of surgically removed human epikeratoplasty lenticules. METHODS: Removed epikeratoplasty lenticules and penetrating keratoplasty buttons that contained epikeratoplasty lenticules were evaluated for duration of epikeratoplasty, histologic and ultrastructural features, and average number of keratocytes per high-power microscopic field. The keratocyte density was compared with age-matched controls. RESULTS: Fifteen epikeratoplasty specimens from eight penetrating keratoplasties and seven removed lenticules were reviewed. The indications for keratoplasty were myopia, keratoconus, and aphakia. The lenticules were in place for 7-120 months, and the keratocyte count ranged from 14 to 40 per high-power field. Keratocyte density increased to 30-40 per high-power field, similar to age-matched controls, at approximately 48 months postoperatively, similar to the density of the controls. Keratocytes appeared to have migrated from the periphery to the center of the lenticules. CONCLUSIONS: Normal keratocyte density in epikeratoplasty lenticules is reached by approximately 48 months after surgery.

Contrast sensitivity and glare disability after radial keratotomy and photorefractive keratectomy.

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 obj ective 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 8000 3 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.