Photorefractive Keratectomy Retreatment Research Articles

Irregular Astigmatism Induced by Irregular Epithelial Remodeling After Conductive Keratoplasty and Transepithelial CXL

PURPOSE: To describe the evaluation and management of irregular astigmatism induced by persistent irregular epithelial remodeling in the absence of persistent underlying stromal curvature irregularity following photorefractive keratectomy (PRK) re-treatment after remote myopic laser in situ keratomileusis (LASIK) with subsequent conductive keratoplasty (CK) and transepithelial corneal cross-linking (CXL). METHODS: Case report. RESULTS: A 41-year-old woman presented for evaluation 1 year after developing blurred vision. She had irregular astigmatism in her right eye following PRK re-treatment for regression after remote myopic LASIK, with a subsequent combined CK and modified transepithelial CXL procedure 1 month after PRK. Scheimpflug tomography demonstrated a post-myopic ablation pattern with an apparent decentered optical zone. Anterior segment optical coherence tomography (AS-OCT) revealed an irregular epithelial thickness pattern, with an asymmetric focal region of epithelial thickness para-centrally temporally. Superficial keratectomy was performed. Following the procedure, the patient's uncorrected distance visual acuity improved by two lines to 20/20, and her subjective blur symptoms resolved and remained stable during 12 months of follow-up. Repeat AS-OCT demonstrated a more uniform epithelial thickness pattern. Scheimpflug tomography showed resolution of the optical zone decentration, confirming that the irregular epithelial remodeling caused the curvature irregularity, and the underlying stromal curvature was not significantly irregular at the time of treatment. CONCLUSIONS: Although uncommon, irregular epithelial remodeling can occur without permanent underlying stromal irregularity. The authors surmise that a temporary induced stromal curvature change from combined CK and transepithelial CXL regressed, but epithelial remodeling did not return to the anticipated regular postoperative pattern. This phenomenon would be unrecognizable in the absence of epithelial mapping and highlights the need for thorough evaluation and targeted management strategies to improve epithelial regularization. [ Journal of Refractive Surgery Case Reports . 2021;1(2):e23–e30.]

Predictors of myopic photorefractive keratectomy retreatment

To determine the factors associated with retreatment after photorefractive keratectomy (PRK) in myopic eyes. Care-Vision Laser Centers, Tel-Aviv, Israel. Retrospective cohort study. A large database on myopic PRK with mitomycin-C (MMC) performed from 2005 to 2012 was studied. Patients were divided into 2 groups according to whether they had retreatment. Multiple preoperative and intraoperative parameters were analyzed for association with retreatment. A total of 9699 eyes of 9699 consecutive patients were studied. The mean age was 25.9years±7.3 (SD); 54.1% were men. The mean preoperative subjective spherical equivalent and astigmatism were -4.30±2.18 diopters (D) (range -0.5 to -13.0 D) and 0.77±0.83 D (range 0 to 6.0 D), respectively. Twohundred twenty-three eyes (2.30%) were retreated. The 2-year retreatment rate decreased from 42 (6.17%) for primary PRK treatments done in 2005 to 2 (0.10%) for primary PRK done in 2012 (R2=0.79, P<.001). Multiple binary logistic regression analysis showed that transepithelial PRK, astigmatism equal to or higher than 3.5 D, and surgeon factor significantly increased theodds of retreatment. Additional parameters significant on univariate analysis alone included age older than 40years, low preoperative sphere, maximum ablation depth less than 45μm, preoperative corrected distance visual acuity better than 20/20, MMC application longer than 40seconds, and optical ablation zone smaller than 7.0mm. The retreatment incidence of PRK has continued to decrease. High astigmatism and transepithelial PRK were associated with increased myopic PRK retreatment rates.

Wavefront-optimized surface retreatments of refractive error following previous laser refractive surgery: a retrospective study.

BackgroundRetreatments are sometimes necessary to correct residual or induced refractive errors following refractive surgery. Many different combinations of primary treatment methods and retreatment techniques have been studied, however, few studies have investigated wavefront-optimized (WFO) technology for retreatment following primary refractive surgery. This study aimed to report the outcomes of WFO photorefractive keratectomy (PRK) retreatments of refractive error following previous laser refractive surgery with PRK, laser in situ keratomileusis (LASIK), or laser-assisted subepithelial keratectomy (LASEK).MethodsWe reviewed records of patients who underwent WFO PRK retreatments using the Allegretto Wave Eye-Q 400 Hz Excimer Laser System (Alcon Surgical) between January 2008 and April 2011 at Walter Reed Army Medical Center and Madigan Army Medical Center. Outcomes were recorded in terms of uncorrected distance visual acuity (UDVA), manifest refraction spherical equivalent (MRSE), corrected distance visual acuity (CDVA), and complications at 1 month (M), 3 M, and 6 M post-op.ResultsSeventy-eight patients (120 eyes) underwent WFO PRK retreatment during the study period. Primary surgery was surface ablation in 87 eyes (78 PRK, 9 LASEK) and LASIK in 33 eyes. The mean spherical equivalent before retreatment was −0.79 ± 0.94 D (−3.00 to 1.88 D). UDVA was ≥ 20/20 in 69 eyes (60.0 %) at 1 M, 54 eyes (71.1 %) at 3 M, and 27 eyes (73.0 %) at 6 M follow-up. MRSE was within ±0.50 D of emmetropia in 78 eyes (67.8 %) at 1 M, 59 eyes (77.6 %) at 3 M, and 25 eyes (67.6 %) at 6 M follow-up. CDVA was maintained within ±1 line of pre-op in 113 of 115 eyes (98.3 %) at 1 M, 74 of 76 eyes (97.4 %) at 3 M, and 37 eyes (100 %) at 6 M follow-up.ConclusionAlthough follow-up was limited beyond 3 M, WFO PRK retreatments in patients with residual refractive error may be a safe and effective procedure. Further studies are necessary to determine the long-term safety and stability of outcomes.

Mitomycin C application in refractive surgery

Over the years, mitomycin C has been used by refractive surgeons to prophylactically decrease haze after surface ablation procedures and therapeutically in the treatment of preexisting haze. Development of mitomycin C treatments has had a significant role in the revival of surface ablation techniques. We reviewed the literature regarding mechanism of action of mitomycin C, its role in modulating wound healing after refractive surgery, and its safety and efficacy as adjuvant therapy applied after primary photorefractive keratectomy surgery or after photorefractive keratectomy re-treatment after laser in situ keratomileusis and other corneal surgeries and disorders. The drug is a potent mitotic inhibitor that effectively blocks keratocyte activation, proliferation, and myofibroblast differentiation. Many studies have suggested that mitomycin C is safe and effective in doses used by anterior surface surgeons, although there continue to be concerns regarding long-term safety. After initial depletion of anterior keratocytes, keratocyte density seems to return to normal 6 to12 months after the use of mitomycin C when corneas are examined with the confocal microscope. Most clinical studies found no difference between preoperative and postoperative corneal endothelial cell densities when mitomycin C 0.02% was applied during refractive surgery,with exposure time of 2 minutes or less. After approximately 14 years of use, mitomycin C has been found to be effective when used for prevention and treatment of corneal haze.

Mitomycin C: Biological Effects and Use in Refractive Surgery

To provide an overview of the safety and efficacy of mitomycin C (MMC) as adjuvant therapy after refractive surgery procedures. Literature review. Over the past 10 years, MMC has been used by refractive surgeons to prophylactically decrease haze after surface ablation procedures and therapeutically in the treatment of preexisting haze. Development of MMC treatments has had a significant role in the revival of surface ablation techniques. We reviewed the literature regarding mechanism of action of MMC, its role in modulating wound healing after refractive surgery, and its safety and efficacy as adjuvant therapy applied after primary photorefractive keratectomy surgery or after photorefractive keratectomy re-treatment after laser in situ keratomileusis and other corneal surgeries and disorders. The drug is a potent mitotic inhibitor that effectively blocks keratocyte activation, proliferation, and myofibroblast differentiation. Many studies have suggested that MMC is safe and effective in doses used by anterior surface surgeons, although there continue to be concerns regarding long-term safety. After initial depletion of anterior keratocytes, keratocyte density seems to return to normal 6 to 12 months after the use of MMC when corneas are examined with the confocal microscope. Most clinical studies found no difference between preoperative and postoperative corneal endothelial cell densities when MMC 0.02% was applied during refractive surgery, with exposure time of 2 minutes or less. After more than 10 years of use, MMC has been found to be effective when used for prevention and treatment of corneal haze. Questions remain regarding optimal treatment parameters and long-term safety.

Mitomycin C in Photorefractive Keratectomy

To evaluate the outcome of primary or retreatment photorefractive keratectomy (PRK) or phototherapeutic keratectomy (PTK) with mitomycin C (MMC) 0.02% applied prophylactically intraoperatively for the prevention of haze and regression in cases of significant haze and regression after primary PRK, due to previous radial keratotomy (RK), in primary PRK eyes with high myopia, and in comeas with a previous superficial foreign body scar. This was a retrospective evaluation of 34 eyes treated with PRK or PTK and intraoperative MMC. Mitomycin C was applied immediately after laser ablation. Postoperative examinations were conducted 3 and 7 days after surgery and monthly for 6 months. Haze was graded on a standard 0+ (clear cornea) to 4+ (total opacity) scale. Visual acuity was measured as a general baseline indicator. Postoperatively, uncorrected visual acuity (UCVA) was 20/20 or better in 21 eyes and 20/25 in 5 eyes with best spectacle-corrected visual acuity (BSCVA) of 20/20 or better. Three eyes achieved UCVA of 20/30 with BSCVA of 20/20 or better; and 5 eyes had UCVA of 20/40 with BSCVA of 20/20 or better. Nineteen (56%) eyes had grade 0+ haze and 15 (44%) eyes had grade 0.5+ haze (trace haze) at 6-month follow-up. Mitomycin C 0.02% used prophylactically during PRK or PTK retreatment was effective in preventing significant recurrent haze from developing. In eyes with high myopia or previous RK or scarring, MMC was effective in preventing significant haze formation.

Corneal wavefront-guided photorefractive keratectomy in patients with irregular corneas after corneal refractive surgery

To evaluate the corrective potential of corneal wavefront-guided photorefractive keratectomy (PRK) in patients with high levels of corneal aberrations and symptoms after previous corneal refractive surgery. Vissum-Instituto de Oftalmológico de Alicante, Alicante, Spain. This study comprised 25 eyes (20 patients) that had 1 or more previous unsuccessful keratorefractive procedure. All eyes had PRK retreatment using the Esiris excimer laser and ORK-CAM software for customized ablation design. All eyes had a high preoperative level of corneal higher-order aberrations (HOAs) (coma-like or spherical-like root mean square [RMS] >0.5 microm). Changes in refractive outcomes, subjective symptoms, and corneal aberrometry were evaluated during a 6-month follow-up. Uncorrected visual acuity improved significantly from preoperatively (mean 0.48) to 6 months after retreatment (mean 0.75) (P<.01). The mean best spectacle-corrected visual acuity (BSCVA) also improved significantly, from 0.78 to 0.90, respectively (P<.01). Forty-four percent of patients gained 1 or more lines of BSCVA. The reduction in cylinder at 6 months was statistically significant (P= .01). Corneal aberrometry at 6 months showed a statistically significant reduction in total (P= .01), spherical-like (P<.01), coma-like (P= .02), and primary coma (P<.01) RMS. At 6 months, 72% of patients had low or no perception of halos and all reported no glare. Corneal wavefront-guided PRK enhancement with the ORK-CAM system minimized corneal HOAs in eyes with previous unsuccessful keratorefractive surgery.

Photorefractive Keratectomy Retreatment After LASIK

This prospective, randomized, controlled trial aims to provide evidence in relation to the efficacy and safety of corneal collagen cross-linking (CXL) in the management of progressive keratoconus. Eligible eyes were separately randomized into either treatment or control groups. Collagen crosslinking was performed using 0.1% riboflavin (in 20% dextran T500) and ultraviolet A (UVA) irradiation (370 nm, 3 mW/cm2, 30 min) in accordance with a previously published protocol. At each review, a full clinical ophthalmic examination was performed including endothelial cell count and confocal microscopy. To date, 66 eyes of 49 patients with documented progression of keratoconus have been enrolled and randomized. Interim analysis of treated eyes showed a flattening of the steepest simulated keratometry value (K-max) by an average of 0.74 diopters (D) (P = .004) at 3 months, 0.92 D (P = .002) at 6 months, and 1.45 D (P = .002) at 12 months. A trend toward improvement in best spectacle-corrected visual acuity was also observed. In the control eyes, mean K-max steepened by 0.60 D (P = .041) after 3 months, by 0.60 D (P = .013) after 6 months, and by 1.28 D (P < or = .0001) after 12 months. Best spectacle-corrected visual acuity decreased by logMAR 0.003 (P = .883) over 3 months, 0.056 (P = .092) over 6 months, and 0.12 (P = .036) over 12 months. No statistically significant changes were found for spherical equivalent or endothelial cell density. Preliminary results of this randomized controlled trial suggest a temporary stabilization of all treated eyes after CXL.

Photorefractive Keratectomy With 0.02% Mitomycin C for Treatment of Residual Refractive Errors After LASIK

To evaluate the efficacy and safety of prophylactic mitomycin C (MMC) during photorefractive keratectomy (PRK) over LASIK flaps for the treatment of residual refractive errors following LASIK. In this single center, retrospective clinical study, 30 eyes of 33 patients (mean age 37.2 years) who had MMC (0.02%, 30 to 120 seconds) during PRK for the treatment of residual refractive errors following myopic LASIK were evaluated. The retreatment procedures were performed with a VISX S4 laser with iris registration. All patients underwent slit-lamp microscopy, manifest and cycloplegic refraction, corneal topography, pachymetry, pupillometry, and wavefront analysis pre- and postoperatively. All patients underwent follow-up at 1 day, 1 week, and 1, 3, and 6 months and thereafter as required. Mean time between LASIK and PRK retreatment was 67.3 months (range: 7 to 113 months). No intra- or postoperative complications occurred during primary LASIK or PRK retreatment. Mean spherical equivalent refraction of attempted correction with PRK was -0.94 diopters (D) (range: -2.38 to +0.75 D). At mean 7.1-month follow-up, the average uncorrected visual acuity (UCVA) improved from 20/50 (range: 20/30 to 20/200) to 20/28 (range: 20/15 to 20/70). Twenty-seven of 30 eyes showed improvement in UCVA. Two eyes had subjective improvement of glare symptoms (and objective improvement in higher order aberrations), and one eye lost one line of best spectacle-corrected visual acuity due to unrelated corneal abrasion in the postoperative period. None of the eyes in the cohort developed postoperative haze. Photorefractive keratectomy with prophylactic MMC (0.02%) is a safe and effective option for treating myopic regression following LASIK. A single intraoperative application of 0.02% MMC for as few as 30 seconds was effective in preventing postoperative haze formation.

Photorefractive Keratectomy Retreatment After LASIK

To study the results of late photorefractive keratectomy (PRK) in corneas originally subjected to LASIK. Seven eyes of seven patients who had LASIK for myopia were retreated with PRK at least 2 years after LASIK. Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), refraction, and haze were evaluated before and after LASIK and after retreatment by PRK. Photorefractive keratectomy retreatment improved BSCVA in six (86%) of seven eyes, and one (14%) eye showed no changes. None of the eyes lost lines of BSCVA. Five of seven eyes developed mild haze, which disappeared before the last postoperative follow-up. Photorefractive keratectomy retreatment performed at least 2 years after LASIK can improve visual acuity. We hypothesize that LASIK-induced corneal nerve damage disturbs corneal wound healing by increasing the tendency for development of haze.

Surface ablation after laser in situ keratomileusis: Retreatment on the flap

To evaluate the safety and efficacy of superficial laser ablation on the flap as a treatment for residual ametropia after laser in situ keratomileusis (LASIK). Private practice refractive surgery center, Utrecht, The Netherlands. This retrospective study comprised 18 eyes of 15 patients who had alcohol-assisted photorefractive keratectomy (PRK) or laser-assisted subepithelial keratectomy (LASEK) retreatment for residual ametropia after LASIK. All patients who had retreatment on the flap between June 2004 and June 2005 were included in the study. Retreatments were performed by wavefront-guided excimer laser surface ablation using the Visx Star S4 laser. Outcome measures included uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), subjective refraction, and biomicroscopy at the 3-, 6-, and 12-month postoperative visits. The preoperative spherical equivalent (SE) refraction was -0.63 diopter (D) +/- 0.87 (SD) (range -2.00 to +1.38 D). The mean amount of ablated cornea was 21.3 +/- 7.4 microm. At 3 months, the mean UCVA was 0.83 +/- 1.5 lines (range 0.40 to 1.25), yielding an efficacy index of 0.87. At 6 months, the mean UCVA increased to 0.98 +/- 0.8 line (range 0.63 to 1.25) and the efficacy index, to 1.03. At 12 months, 6 eyes were lost to follow-up. The mean UCVA was 0.83 +/- 2.2 lines (range 0.20 to 1.25), with an efficacy index of 0.87. The mean BSCVA was 0.98 +/- 0.9 line (range 0.80 to 1.25) at 3 months and 1.05 +/- 0.6 line (range 0.80 to 1.25) at 6 months, yielding a safety index of 1.03 and 1.11, respectively. At 12 months, the mean BSCVA was 0.95 +/- 1.0 line (range 0.63 to 1.25), with a safety index of 1.0. At 6 months, no eye had lost lines of BSCVA, 11 eyes had no change, and 7 eyes gained 1 line. At 12 months, 2 eyes lost 1 line of BSCVA, 8 eyes had no change, and 2 eyes gained 1 line. The mean SE refraction was +0.10 +/- 0.27 D (range -0.25 to +0.63 D) at 3 months, +0.06 +/- 0.37 D (range -0.50 to +1.13 D) at 6 months, and +0.15 +/- 0.39 D (range -0.50 to +0.88 D) at 12 months. On biomicroscopic examination, 1 eye had prolonged grade 1 haze that disappeared before 6 months. Two eyes of 1 patient who had hyperopic retreatment developed late-onset haze 8 months postoperatively. Eyes with microstriae in the flap before retreatment showed significant improvement after retreatment. There were no sight-threatening complications. Wavefront-guided LASEK or alcohol-assisted PRK retreatment on the surface of a LASIK flap was safe and effective in correcting small amounts of residual myopia.

Repeated photorefractive keratectomy for undercorrection and regression.

Regression (often combined with significant haze) and undercorrection are the most frequent complications after photorefractive keratectomy (PRK) for myopia. PRK retreatment has been used to treat both of these complications. Sixty-three eyes (55 patients) were reoperated (PRK) because of initial regression or undercorrection. The mean interval between the operations was 17.2 months (range 5 to 37 mo). Residual myopia before retreatment was less than -5.00 D in 62 eyes (mean -2.21 +/- 0.99 D) and was -10.50 D in one eye. The same surgical PRK technique (Aesculap-Meditec MEL 60 excimer laser with 5 or 6-mm ablation zone) was used in both operations. One-year results were available for 51 eyes. In the group of eyes with low residual myopia (<-5.00 D), mean refraction 1 year after retreatment was -0.42 +/- 0.96 D and 43 eyes (86%) were within +/-1.00 D of emmetropia. Uncorrected visual acuity of 20/40 or better was achieved in 43 eyes (86%) after 1 year. One eye lost two lines of best spectacle-corrected visual acuity after two procedures because of haze. Mean haze was the same before and 12 months after reoperation (grade 0.39 vs. 0.38). Significant haze (>2) and high regression after the first PRK occurred after reoperation. The one eye with -10.50 D residual myopia after the first PRK showed high regression, and 1 year after the reoperation refraction was -9.50 D with grade 2 haze. Repeated PRK was safe and in most cases effective in treating regression and undercorrection in eyes with low residual myopia after initial PRK. High regression and especially haze after the initial PRK often reappeared after reoperation.

Iatrogenic keratectasia after laser in situ keratomileusis for less than −4.0 to −7.0 diopters of myopia

Purpose To study 13 eyes with less than −4.0 to −7.0 diopters of myopia that developed central or inferior keratectasia after laser in situ keratomileusis (LASIK). Methods The progress of the ectasia was determined by a series of pre- and post-LASIK topographies and the case histories. Results Progressive ectasia developed from 1 week to 27 months after LASIK. This necessitated the wearing of hard contact lenses or penetrating keratoplasty. One eye improved for some months after photorefractive keratectomy retreatment. Two eyes in 1 patient and 1 eye in a second patient had latent keratoconus before surgery. Conclusion Laser in situ keratomileusis can cause permanent weakening and ectasia of the cornea even in eyes with low myopia.

Apical nodular subepithelial corneal scar after retreatment in hyperopic photorefractive keratectomy

PurposeTo report a complication, apical nodular subepithelial corneal scar, that can occur after hyperopic photorefractive keratectomy (PRK) retreatment. SettingIstanbul University Eye Research Center, Istanbul, Turkey. MethodsTwelve eyes of 6 patients with apical nodular subepithelial corneal scar were retrospectively studied. Mean age of the 5 men and 1 woman was 30.2 years ± 5.4 (SD). All eyes had hyperopic PRK retreatment for regression 9.5 ± 1.44 months after primary hyperopic PRK. Mean spherical equivalent refraction of the residual hyperopia before retreatment was +4.67 ± 0.81 diopters (D). All patients had a corneal haze grade of less than 1+. Hyperopic PRK retreatment was performed with a 193 nm excimer laser (Chiron Technolas Keracor 116). ResultsApical nodular subepithelial corneal scars developed within the first month of hyperopic PRK retreatment and progressed until the third month in 12 eyes of 6 patients. The lesion was round and symmetrical in both eyes, smaller than 2.0 mm, and centrally located. During the mean 40.66 ± 2.46 month follow-up, the lesion did not change in size or density. Mean spherical equivalent refraction after retreatment was 2.88 ± 0.88 D (range +1.50 to +4.00 D) at 1 month and +4.36 ± 1.83 D at last follow-up. Refraction was unmeasurable in 3 eyes. Five eyes lost 1 line of best spectacle-corrected visual acuity and 7 eyes, 2 or more lines. The surface regularity indexes were higher than 2.00 in all the eyes. ConclusionHyperopic PRK retreatment may cause the sight-threatening complication of apical nodular subepithelial corneal scar. This complication behaves unlike corneal haze and does not resolve spontaneously over time.

Epithelial scrape for photorefractive keratectomy overcorrection associated with induced regression.

To study the effect of combined corneal epithelial scrape and contact lens wear treatment on regression in eyes with symptomatic overcorrection after photorefractive keratectomy (PRK) or PRK retreatment. Fifteen eyes had corneal epithelial scrape with a scalpel followed by soft contact lens wear for approximately 1 month. Eight of the eyes were treated 3-4 months after the laser procedure, and seven eyes were treated >4 months after laser treatment. Fifteen eyes that had the same level of PRK correction and monitored during the same interval after PRK were used as matched control eyes. Epithelial scrape was performed for mean spherical equivalent (SE) of +1.1+/-0.4 diopters (D) (range, +0.50 to +1.75 D) at mean 6.1+/-3.2 months after PRK or PRK retreatment. The SE in these eyes was +0.5+/-0.6 D (range, -0.25 to +1.25 D) 3 months after epithelial scrape and +0.4+/-0.5 D (range, -0.75 to +1.25 D) 6 months after scrape. The change in scraped eyes at 3 and 6 months compared to before scrape was statistically significant (p = 0.001 and p = 0.001, respectively). The change in mean SE at 6 months after scrape (-0.7+/-0.5 D) was significantly different than the change noted in matched control eyes that were not scraped (-0.1+/-0.2 D) over the same interval after the PRK or PRK retreatment procedure. The change in SE at 6 months after epithelial scrape was greater for the eyes scraped 4 months or less (mean, 3.6+/-0.5 months) after PRK (-0.9+/-0.3 D) than eyes scraped >4 months (9.0+/-2.6 months) after PRK (-0.4+/-0.5 D). This difference approached statistical significance (p = 0.06). Epithelial scrape and soft contact lens treatment for symptomatic overcorrection after PRK may induce regression and is more likely to be effective when performed <4 months after the primary PRK or PRK retreatment procedure.

Photorefractive keratectomy retreatments: Comparison of two methods of excimer laser epithelium removal

Background Regression and undertreatment after initial photorefractive keratectomy (PRK) in higher myopes is not unusual. Patients frequently desire 20/20 uncorrected vision, which necessitates retreatments or enhancements. However, the safest and most efficacious way to treat these patients has not yet been established. This study evaluates two techniques of PRK enhancements, comparing two different methods of laser epithelial removal. Design Retrospective, nonrandomized, comparative trial. Participants A total of 224 eyes. Methods Eyes were identified that had 6-month follow-up after a PRK enhancement from February 1995 through February 1997. Two methods of treatment were identified. The same VISX 20/20B laser in the same clinic was used for all retreatments. Group I patients had a total removal of the epithelium in a mode phototherapeutic keratectomy (PTK) prior to the refractive ablation. Group II patients had a total laser epithelial removal in two steps prior to the refractive ablation. The first step was a PRK and then a PTK. Main outcome measure The disappearance of epithelial fluorescence was the end point for the PTK ablation in groups I and II. Results There were 131 eyes in group I and 93 eyes in group II. The mean spherical equivalent (SE) prior to the original PRK in group I was −7.5 diopters (D) ± 3 D and in group II was −7.75 D ± 2.34 D. The mean SE prior to the PRK retreatment in group I was −2.22 D ± 1.29 D and in group II was −1.89 D ± 0.83 D. The mean postoperative 6-month SE after the PRK enhancement in group I was −0.05 D ± 0.80 D and in group II was 0.01 D ± 1.08 D. A greater proportion of group I eyes (7.8%) had arcuate haze and a hyperopic shift from the 1- to 6-month postoperative visit ( P = 0.03). Conclusions A two-step laser epithelial removal compared with a one-step PTK epithelial laser removal in PRK retreatments provides a more even and confluent epithelial removal, less risk of arcuate haze development, and less risk of a hyperopic shift from 1 to 6 months after the retreatment.

Epithelial removal with the excimer laser (laser-scrape) in photorefractive keratectomy retreatment

Objectives To retrospectively evaluate refractive and topographic outcomes after excimer laser photorefractive keratectomy (PRK) retreatment using the laser-scrape technique for epithelial removal. Design Retrospective clinical study. Participants Thirty eyes of patients who had PRK retreatment for undercorrection after primary PRK were examined. Intervention The PRK retreatment was performed using a laser-scrape technique in which the excimer laser was used to remove the majority of the epithelium overlying the anterior stromal surface before additional PRK ablation. Main outcome measures Uncorrected visual acuity, best-corrected visual acuity (BCVA), surface regularity index (SRI), and surface asymmetry index were measured. Results Primary PRK was performed for myopia of −5.1 ± 1.7 diopters (range, −1.1 to −7.5 diopters). Mean spherical equivalent (SE) was −1.3 ± 0.4 diopters (range, −0.6 to −2.0 diopters) before retreatment. Mean SE 6 months after retreatment decreased to +0.1 ± 0.4 diopter (range, +1.25 to −0.75 diopters; P < 0.0001). Four eyes (15%) were more than +0.5 diopter overcorrected at 6 months. Ninety-six percent of eyes achieved mean SE within ±1 diopter and 77% within ±0.5 diopter of emmetropia after retreatment. Visual acuity improved significantly 6 months after reablation ( P < 0.0001) with 100% 20/40 or better and 73% 20/25 or better without correction. Final BCVA also improved compared with before retreatment ( P = 0.02). Twelve eyes gained 1 line of BCVA and no eye lost more than 1 line of BCVA. The SRI before retreatment was 0.6 ± 0.3 (range, 0.0–0.9) and remained the same 0.6 ± 0.2 (range, 0.1–1.0; P = 0.8), 6 months after retreatment. Conclusion Excimer laser PRK retreatment using the laser-scrape technique for epithelial removal is an accurate and safe procedure for treating undercorrection of eyes after PRK for low-to-moderate myopia.

Laser in situ keratomileusis after photorefractive keratectomy for myopic regression

Purpose: To assess the efficacy and safety of laser in situ keratomileusis (LASIK) for regression after excimer laser photorefractive keratectomy (PRK).Setting: Eye Research Center, Istanbul University; Istanbul, Turkey.Methods: Laser in situ keratomileusis to treat residual myopia ranging from, 1.50 to 12.50 diopters (D)(mean 5,96 D ± 3.06 [SD]) was performed in 45 eyes of 25 patients. Cylindrical corrections were done in 7 eyes (15.6%) and spherical ablations, in 38 (84.40. The mean interval between primary PRK and LASk retreatment was 18.50 ± 8.12 months. The procedure was performed under a hinged corneal flap using the Chiron Automated Corneal Shaper and Chiron Keracor 116 excimer laser.Results: Six months after LASIK retreatment, mean spherical equivalent refraction was -0.67 ± 0.77 D. Thirty-six eyes (80%) were within ± 1.00 D of emmetropia. Uncorrected visual acuity was 20/40 or more in 31 eyes (68.9%), 2 eyes (4%) lost 2 lines of best spectacle-corrected visual acuity. There was no statistically significant difference in corneal haze before and after LASIK.Conclusion: Laser in situ keratomileusis was safe and effective for treating residual myopia after excimer laser PRK.