Repeated photorefractive keratectomy for undercorrection and regression

PURPOSE: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.     

Analysis of refractive state after excimer laser photorefractive keratectomy in myopia]

OBJECTIVE: To evaluate refractive state after excimer laser photorefractive keratectomy (PRK) in patients with myopia. METHODS: 234 cases(391 eyes) followed up for two years were divided into two groups, group I: mild and moderate myopia(< or = -6.00 D), 228 eyes; group II: High myopia(> -6.00 D), 163 eyes. The refractive state of patients at three, six, twelve and twenty-four months postoperatively were monitored. RESULTS: At two years after photorefractive keratectomy (PRK), refractive regression (> -0.5 D), overcorrection(> 1.00 D), undercorrection(> 1.00 D), postoperative residual astigmatism postoperative astigmatism and hyperopia shift in group I were 1.7%, 4.4%, 5.7%, 12.8%, 7.4% and 7.5% respectively, while in high myopia group were 15.9%, 4.9%, 23.3%, 29.7%, 31.1% and 6.7% respectively. CONCLUSION: The results prove that photorefractive keratectomy is an effective, precise, stable and safe method for correction of mild and moderate myopia, but insufficient for high myopia.     

Induced astigmatismafter photorefractive keratectomy

Purpose:To retrospectively analyze a group of patients to determine whether their induced astigmatism was caused by asymmetry in the laser beam, asymmetry in ablation rates, or wound healing in different corneal meridians.Setting:Single-center physician office.Methods:In this study, 146 eyes of 116 patients who had photorefractivakeratectomy(PRK) for myopia with the Apex laser (Summit Technology) were retrospectively identified. In 28 eyes, the patient's chair had been rotated 90 degrees from its usual position under the laser. The vector-summated mean change in astigmatism in eyes with the chair rotated 90 degrees was compared with that in a group of control eyes in which the chair was in the usual position.Results:The vector-summated mean change in the control eyes was 0.30 diopter (D)at 83 degrees. Forty-eight of 113 eyes (42.5%) had induced with-the-rule (WTR) astigmatism, and 14 of 113 eyes (12.4%) had induced against-the-rule (ATR) astigmatism. In the eyes in which the chair was rotated 90 degrees, vector-summated mean change was 0.10 D at 13 degrees (P < .0005). One of 27 eyes (3.7%) had induced WTR astigmatism, and 13 of 27 eyes (48.1%) had induced ATR astigmatism (P < .001, chi-square).Conclusion:Astigmatism induced by myopic PRK with the Apex laser was small. The axis of induced astigmatism rotated 90 degrees when the patient's chair was rotated, implying that it is inhomogeneities in the beam rather than meridional asymmetry in ablation rates or wound healing that are responsible for induced astigmatism.[]     

Eight-year follow-up of photorefractive keratectomy for myopia

PURPOSE: We evaluated 8-year results of excimer laser photorefractive keratectomy (PRK) for myopia in terms of stability and late complications. METHODS: Ninety-two myopic eyes of 55 patients were treated with a single-step method using an Aesculap-Meditec MEL 60 excimer laser with a 5.0-mm ablation zone. Treated eyes were divided into three groups according to preoperative refraction: low myopes (< or = -6.00 D), medium myopes (-6.10 to -10.00 D), and high myopes (>-10.00 D). RESULTS: Change in myopic regression stabilized in all myopia groups within 12 months, although a small myopic shift occurred up to 8 years after PRK. Mean change in refraction between 2 and 8 years was -0.42 +/- 0.48 D for low myopes, -0.37 +/- 0.34 D for medium myopes, and -0.41 +/- 0.50 D for high myopes. The percentage of eyes within +/- 1.00 D of emmetropia 8 years after PRK was 78.3% in the low myopia group, 68.8% in the medium myopia group, and 57.1% in the high myopia group. One eye lost 2 lines of best spectacle-corrected visual acuity due to irregular astigmatism. In 13.0% of eyes, a residual trace corneal haze was observed, which had no effect on visual acuity. Apart from the loss of 2 lines of BSCVA in one eye, there were no other late complications during the study period. CONCLUSIONS: The mean change in refraction between 2 and 8 years was less than -0.50 D, regardless of preoperative refraction, and may be attributed to natural age-related refractive change. The appearance of residual corneal haze after 8 years correlated with the amount of myopic correction. PRK was a safe and stable surgical procedure in this group of patients.     

Correction of myopic astigmatism by combined treatment with PRK and T-incision and photoastigmatic refractive keratectomy

Background: In contrast to the correction of simple myopia there is no widely accepted technique for the correction of myopic astigmatism. Currently two techniques are available: the photoastigmatic refractive keratectomy (PARK) and the combination of arcuate keratotomies with standard PRK (PRK-T). Methods: In two groups, 67 patients underwent a correction of myopic astigmatism in a total of 87 eyes (19 by PRK-T and 68 by PARK), and were followed for 1 year. The spherical equivalent was − 6.7 D in both groups and the refractive astigmatism ranged from − 1.0 to − 6.5 D. The PARK procedure was performed by means of an elliptic ablation (Kertom I, Schwind) with a 5.8 × 8.1 mm zone. The PRK-T technique consisted of two arcuate keratotomies with a free optical zone of 7 mm and a standard myopic PRK at least 6 weeks later. Results: The 1 year follow-up was completed in 57 out of 87 eyes included in the study. At 1 year post-operation, 83 % of the PRK-T group and 80 % of the PARK group had an uncorrected visual acuity of 20/40 or better. The refractive astigmatism was reduced by 76 % in the PRK-T group and by 67 % in the PARK group. The spherical equivalent was − 0.59 ± 1.1 D at 1 year after PRK-T and − 0.28 ± 1.04 D after PARK. In three eyes of the PARK group (6.7 %) a visual loss of more than one Snellen line occured. Two of these eyes had a preoperative myopia of more than − 6 diopters. Conclusion: Both techniques have the potential to reduce myopic astigmatism, however, the success rate is not as high compared to spherical PRK. Also, the complication rate of 2.5 % in corrections to − 6 D is significantly higher than that with spherical myopic PRK.      

Photorefractive keratectomy for residual myopia after cataract surgery

PURPOSE: To evaluate the effectiveness, predictability, and safety of photorefractive keratectomy (PRK) for correcting residual myopia and myopic astigmatism after cataract surgery with intraocular lens implantation. SETTING: Refractive Surgery and Cornea Unit, Instituto Oftalmológico de Alicante, Alicante, Spain. METHODS: Thirty consecutive eyes (30 patients) had PRK for residual myopia after cataract surgery. Surface PRK with a VISX Twenty-Twenty excimer laser was used in all patients. Follow-up was 1 year. RESULTS: Before PRK, no eye had an uncorrected visual acuity (UCVA) of 20/40 or better. Twelve months after PRK, 16 eyes (53.33%) had a UCVA of 20/40 or better. After PRK, best corrected visual acuity (BCVA) improved 1 line or more in 14 eyes (46.66%) over the preoperative values, and 15 eyes (50.00%) had the same BCVA as before PRK. Mean pre-PRK refraction of -5.00 diopters (D) +/- 2.50 (SD) decreased significantly to -0.25 +/- 0.50 D at 12 months (P < .001). At 12 months, the spherical equivalent was within +/- 1.00 D of emmetropia in 27 eyes (90.00%). No vision-threatening complications occurred. CONCLUSION: Photorefractive keratectomy was an effective, predictable, and safe procedure for correcting residual myopia and myopic astigmatism after cataract surgery.     

准分子激光屈光性角膜切削术后的再治疗

目的 评价准分子激光屈光性角膜切削术（ｐｈｏｔｏｒｅｆｒａｃｔｉｖｅ ｋｅｒａｔｅｃｔｏｍｙ,ＰＲＫ）术后因屈光回退,欠矫出现的残留近视及严重角膜上皮下雾状混沌（ｈａｚｅ）而再次手术治疗的疗效及安全性。方法 采用准分子激光仪对－１．００～－１６．５０Ｄ的近视眼及近视散光患者进行治疗。ＰＲＫ术后３５例（５１只眼）患者出现残留近视及严重ｈａｚｅ。结合ＰＲＫ手术及准分子激光治疗性角膜切削术（ｐｈｏｔｏｐ     

准分子激光屈光性角膜切削术后屈光回退的多因素分析

目的：探讨准分子激光屈光性角膜切削术后屈光回退的主要因素。方法：采用VISX20／20型准分子激光仪对121例214眼近视患者行准分子激光角膜切削术,术后随访2年。分二组进行比较,Ⅰ组为低中度近视（－1．00D－－6．00D）124眼,Ⅱ组为高度近视（－6．25D－－16．00D）90眼。结果：术后2年低中度近视回退率9．7％,高度近视回退率27．8％（P＜0．005）,高度近视中高龄组较低龄组回退率高（P＜0．005）,较严重的角膜上皮下雾状混浊与回退伴行。结论：准分子激光角膜切削术后屈光回退的主要因素有预期矫正屈光度,角膜Haze及年龄。     

Scanning laser polarimetry in corneal topographic changes after photorefractive keratectomy

Purpose: To examine whether, or not, corneal topographic changes after excimer laser photorefractive keratectomy (PRK) for myopia and myopic astigmatism have any influence on measurements of the retinal nerve fiber layer (NFL) with scanning laser polarimetry. Methods: Retinal NFL thicknesses were determined by scanning laser polarimetry in 17 eyes of 13 patients with myopia and myopic astigmatism before and after PRK. Total ablation depth ranged from 26 to 71 μm. We used the relative ratios for superior and inferior NFL thicknesses which were calculated by dividing the NFL values of respective regions by the nasal value. Results: The mean superior NFL ratio measured was 3.02 ± 0.92 preoperatively, and 3.00 ± 0.76 postoperatively. The mean inferior NFL ratio was 2.95±0.75 preoperatively, and 2.99±0.66 postoperatively. There was no statistically significant difference between preoperative and postoperative NFL measurements (Wilcoxon signed rank test, p > 0.05). Conclusions: Corneal topographic changes after PRK have no significant influence on NFL measurements by scanning laser polarimetry. Our results suggest that scanning laser polarimetry can be used as a reliable method for retinal NFL thickness measurements even after excimer laser PRK. This revised version was published online in July 2006 with corrections to the Cover Date.     

The LADAR6000: results in highly myopic and highly astigmatic eyes

PURPOSE: To investigate the early clinical outcomes of the Alcon LADAR6000 system in treating two difficult patient populations: those with high myopia and those with high astigmatism. METHODS: Two series of eyes were of interest and subsequently enrolled in the study. Thirty-three eyes with preoperative manifest refraction spherical equivalent (MRSE) > -6.00 diopters (D) (high myopia group) and 25 eyes with preoperative myopic astigmatism > -1.50 D (high myopic astigmatism group) were enrolled. Mean patient age was 35 years in the high myopia group and 33 years in the astigmatism group. For the high myopia group, the mean preoperative MRSE was -8.13 D (range: -6.25 to -12.5 D). For the high myopic astigmatism group, the mean preoperative astigmatism was -1.89 D (range: -1.50 to -4.50 D). All LASIK flaps were made using a femtosecond laser with superior hinge position. Stromal ablation was performed using the LADAR6000 system for conventional treatment. All eyes were targeted for emmetropia. RESULTS: Both groups of eyes experienced excellent clinical outcomes with 100% of eyes within +/-1.00 D of attempted correction at 1 month. For the high myopia group, mean postoperative MRSE was -0.10 D at 1 month. For the high myopic astigmatism group, mean postoperative MRSE was -0.06 D at 1 month. CONCLUSIONS: The LADAR6000 system produced excellent early clinical outcomes in two challenging patient groups using LASIK with femtosecond laser flaps.     

Surgically induced astigmatism after hyperopic and myopic photorefractive keratectomy

PURPOSE: To compare the axis and magnitude of surgically induced refractive astigmatism (SIA) after hyperopic and myopic photorefractive keratectomy (PRK). SETTING: Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, Texas, USA. METHODS: In this single-center retrospective study, the VISX Star S2 excimer laser was used to create a peripheral annular ablation profile to correct spherical hyperopia in 23 eyes of 16 consecutive patients. Attempted corrections ranged from +0.50 diopter (D) to +4.25 D with 0 to 1.00 D of astigmatism. The same laser was used to create a central ablation profile to correct spherical myopia in 25 eyes of 17 consecutive patients. Attempted corrections ranged from -2.25 to -6.50 D with 0 to 1.00 D of astigmatism. The absolute change in refractive astigmatism was calculated by taking the difference in magnitudes of astigmatism before and after laser treatment without regard to axis. Axis and magnitude of SIA were analyzed by vector differences. Magnitudes were compared using the Student t test, and axial shifts were compared using the chi-square test. All patients were followed for a minimum of 6 months. RESULTS: The mean changes in absolute astigmatism were 0.29 +/- 0.28 D at 3 months and 0.34 +/- 0.29 D at 6 months after hyperopic PRK and 0.40 +/- 0.35 D at 3 months and 0.39 +/- 0.36 D at 6 months after myopic PRK. The mean vectoral magnitudes were 0.49 +/- 0.29 at 3 months and 0.52 +/- 0.25 at 6 months after hyperopic PRK and 0.48 +/- 0.39 at 3 months and 0.44 +/- 0.38 at 6 months after myopic PRK. The mean values for SIA (the centroid) were 0.10 +/- 0.57 D x 113 degrees at 3 months and 0.15 +/- 0.57 D x 131 degrees at 6 months after hyperopic PRK and 0.04 +/- 0.63 D x 160 degrees at 3 months and 0.08 +/- 0.58 D x 171 degrees at 6 months after myopic PRK. There was no statistically significant difference between the 2 groups in vectoral axis or magnitude of SIA. CONCLUSION: Surgically induced astigmatism after hyperopic PRK was comparable to astigmatism induced by myopic PRK. A peripheral annular ablation for hyperopic correction, similar to a central ablation in myopic PRK, did not appear to result in uneven corneal healing causing astigmatism.     

LASIK versus PRK for high astigmatism

Purpose

To compare the refractive outcomes of laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) for myopic astigmatism of 3 diopters (D) or more.

Study design

Retrospective matched comparative study.

Methods

This study include consecutive myopic patients (SE 0 to –10 D) undergoing LASIK or PRK between 2007 and 2016 with astigmatism of 3 to 6 D, and postoperative follow-up of at least 30 days for LASIK and 60 days for PRK, compared outcomes of LASIK and PRK eyes.

Results

The LASIK and PRK groups comprised 175 eyes of 175 patients each, with median follow-up of 39 and 139 days, respectively (P?<?0.001). Mean preoperative manifest astigmatism was –3.35?±?0.46 and –3.42?±?0.51 D (P?=?0.92), postoperative SE was –0.43?±?0.55 and –0.16?±?0.64 D (P?<?0.001), and arithmetic astigmatism was –0.59?±?0.46 and –0.88?±?0.60 D (P?<?0.001), for the LASIK and PRK groups, respectively. Fifty-seven and 64.0% eyes had postoperative SE within?±?0.5 D of emmetropia (P?=?0.19), and 57.7 and 38.8% eyes were within 0.5 D of attempted astigmatic correction (P?<?0.001) for the LASIK and PRK groups, respectively. More PRK eyes were overtreated regarding both SE and astigmatism than LASIK eyes (P?<?0.001). The efficacy and safety indices were close to 1.0 in both groups. The surgically induced astigmatism, magnitude of error, index of success, correction index and flattening index were all better in the LASIK group.

Conclusion

Both LASIK and PRK achieve good outcomes in high astigmatism. LASIK achieved mild superiority over PRK.

     

The safety and efficacy of photorefractive keratectomy after laser in situ keratomileusis

PURPOSE: To determine the safety and efficacy of performing photorefractive keratectomy (PRK) in corneas previously treated with laser in situ keratomileusis (LASIK) surgery. METHODS: Fifteen eyes of 14 patients who had initially received LASIK for the treatment of myopia and compound myopic astigmatism were evaluated. Variables included existence of and/or type of flap complication associated with the original LASIK procedure, refractions before and after (3 and 6 months) PRK, uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), and the development of complications after PRK such as haze, scarring, double vision, or ghosting. RESULTS: All 15 eyes were available for analysis at 6 months. Eleven eyes had experienced flap complications during the initial LASIK procedure and 4 eyes had experienced complications in the LASIK postoperative period. Characteristics prior to performing PRK included 11 myopic and 4 hyperopic eyes. By 6 months after PRK treatment, 87% of eyes had UCVA > or = 20/40, 53% had > or = 20/25, and 40% had > or = 20/20. All eyes had BSCVA of > or = 20/30, with 73% being > or = 20/20. No eye had lost 2 lines of BSCVA and only 1 eye lost 1 line of BSCVA. Sixty percent of eyes were within 1.0 diopters (D) of emmetropia, and 40% were within 0.5 D of emmetropia. A trend towards undercorrection and surgical induction of astigmatism as confirmed by vector analysis was noted. No eye developed significant haze or scarring. CONCLUSIONS: Photorefractive keratectomy may be a safe procedure to perform in corneas previously treated with LASIK surgery. Results show good reduction of refractive error and improvement of UCVA and BSCVA. A significant undercorrection of astigmatism was attributed to surgically induced astigmatism. Further studies are necessary to determine the long-term safety and stability of outcomes.     

The excimer laser for corneal refractive surgery—recent developments and evolutionary directions

This article reviews recent developments in excimer laser refractive corneal surgery. The excimer laser is now used to treat myopia, hyperopia and astigmatism by either surface (photorefractive keratectomy or PRK) or stromal (laser in situ keratomileusis or LASIK) ablation. The refractive outcome of PRK is excellent for low (less than six dioptres) myopia, but it is not without complications. These include initial severe pain, myopic regression, haze, glare, halos and difficulty with vision in reduced light. The refractive outcome for LASIK is similar to that for PRK, but there is negligible pain, much less haze, less regression among highly myopic patients and a more rapid establishment of final unaided visual acuity. Although excimer laser treatment is currently available, some important advances are necessary before the spectacle and contact lens markets are threatened. Control of the healing process is crucial to improve the accuracy of the outcome, reduce regression and eliminate haze. More attention must be paid to the visual outcome and ablation design so that visual functions, such as best corrected visual acuity and contrast sensitivity, are not reduced. It even may be possible, in the future, to custom design aspheric ablations to yield improved best corrected visual acuity.     

准分子激光角膜原位磨镶术矫治高度近视准分子激光屈光性角膜切削术后屈光回退的临床观察

目的评价准分子激光角膜原位磨镶术（LASIK）矫治高度近视准分子激光屈光性角膜切削术（PRK）后屈光回退的疗效。方法回顾性临床研究。对PRK术后2年以上、屈光回退且屈光度稳定的患者8例14眼行LASIK,对LASIK术后术眼进行评价。患眼PRK术前屈光度为-6.25～-12.50 D,PRK术后屈光度为-1.50～-6.25 D。随访观察LASIK矫正1年后术眼的裸眼视力、最佳矫正视力、屈光度、上皮下雾状混浊（haze）形成和角膜厚度的变化。结果所有患眼术后主观症状较轻。LASIK术后1年平均球镜度数为（-0.62±0.94）D。LASIK术后0.5≤裸眼视力〈0.8者4眼,≥0.8者9眼,1眼（7.1%）最佳矫正视力下降2行。4眼术后出现不同程度的haze,包括2级haze 3眼、3级haze 1眼。应用氟米龙滴眼液1个月后,haze及屈光回退减轻;术后1年,1级haze 2眼,2级haze 2眼,3级haze 1眼。LASIK术前角膜厚度为（467±38）μm,术后为（422±21）μm。结论高度近视PRK术后屈光回退行LASIK矫治是一种可行的方法,但少数患者术后可出现haze,仍需治疗。     

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

ObjectivesTo retrospectively evaluate refractive and topographic outcomes after excimer laser photorefractive keratectomy (PRK) retreatment using the laser-scrape technique for epithelial removal.DesignRetrospective clinical study.ParticipantsThirty eyes of patients who had PRK retreatment for undercorrection after primary PRK were examined.InterventionThe 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 measuresUncorrected visual acuity, best-corrected visual acuity (BCVA), surface regularity index (SRI), and surface asymmetry index were measured.ResultsPrimary 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.ConclusionExcimer 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.     

Evaluation of photorefractive keratectomy retreatments after regressed myopic laser in situ keratomileusis

PURPOSE: To evaluate the results of photorefractive keratectomy (PRK) enhancements in eyes previously treated by myopic laser in situ keratomileusis (LASIK) showing an undercorrection due to either a refractive regression or a primary undercorrection, when an in-the-bed enhancement was not advisable because of residual stromal thickness limitations. DESIGN: Noncomparative, prospective, interventional case series. PARTICIPANTS: Seventeen eyes of 17 patients previously treated by LASIK for a spherical equivalent (SE) correction of -8.125 to -12.50 diopters (D; mean, -9.45 +/- 1.01 D), that after a follow-up of 6 to 14 months ended up with a refraction of -1.50 to -3.75 D (SE; mean, -2.48 +/- 0.74 D). Intended flap thickness was 160 microm for all eyes. In all cases, the residual stromal bed under the flap was considered too thin (255-305 microm) to allow an in-the-bed enhancement without exceeding an assumed safety thickness limit (250 microm). INTERVENTION: Eyes were treated by PRK at least 6 months after LASIK. The PRK ablation parameters (diameter, attempted correction) were selected to avoid theoretical flap perforation. The deepest ablation was 60 microm, for a -3.75-D correction. We used a Bausch & Lomb 217 C excimer laser (Bausch & Lomb, Rochester, New York). MAIN OUTCOME MEASURES: Refraction, uncorrected and best-corrected visual acuity (BCVA), slit-lamp evidence of corneal opacity or other visible complications, and corneal topography. RESULTS: Although the initial postoperative period was characterized by very satisfactory refractive results (mean SE error at 1 month, -0.04 +/- 0.37 D; range, +0.75 to -0.625 D), during follow-up, a dense haze (grade 3 and 4) developed in 14 eyes (82.3%) that induced a further myopic regression (SE, -1.725 to -5.50 D; mean, -3.11 D) and BCVA loss (two to six lines). These 14 eyes underwent a further surgical treatment to remove the severe haze at 3 to 10 months after PRK. CONCLUSIONS: Based on these results, we strongly advise against PRK as a possible option to correct eyes previously treated by myopic LASIK that resulted in an undercorrection.     

Five-year follow-up of photorefractive keratectomy for myopia

PURPOSE: To analyze long-term results of photorefractive keratectomy (PRK) for myopia and myopic astigmatism. METHODS: This retrospective study included 15 eyes of 8 patients who were examined annually for 5 years after PRK. The Nidek EC-5000 laser with an ablation zone of 5.0 mm was used. Evaluations included spherical equivalent manifest refraction, uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), corneal haze, and corneal astigmatism calculated by Fourier analysis of videokeratography data. RESULTS: A tendency toward myopic regression was most evident within the first postoperative year, with manifest refraction changing from +0.80 +/- 1.62 D at 1 week to -0.45 +/- 0.70 D at 1 year postoperatively (P = .007). Regression continued after the second postoperative year. There was a statistically significant difference between manifest refraction at 2 years (-0.36 +/- 0.75 D) and 5 years (-1.11 +/- 1.12 D) (P = .002). Postoperative UCVA stabilized from 3 months up to 3 years, but slightly deteriorated at 4 years and thereafter due to the myopic refractive shift. BSCVA remained stable throughout the 5-year follow-up period. Several eyes developed mild corneal haze after surgery, but haze was minimal in the majority of patients by 1 year and continued to fade over time. The asymmetry component of the cornea significantly increased after surgery, with all postoperative values significantly higher than before PRK (P < .05). Higher order irregularity increased after surgery, with a statistically significant difference between preoperative and 1 year postoperative (P < .05), but values after 2 years were not different from preoperative baseline. CONCLUSION: Fifteen eyes with a baseline refraction of -3.00 to -9.00 D had PRK with the Nidek EC-5000 laser and a 5-mm-diameter ablation zone. Myopic regression occurred in the first year, with continued mild regression of approximately -0.75 D between 2 and 5 years. Nevertheless, the results show the procedure was relatively safe and effective in this group.     

Surgically induced astigmatism after photorefractive keratectomy with the excimer laser

PURPOSE: To evaluate retrospectively the effect of spherical excimer laser photorefractive keratectomy (PRK) on astigmatism. METHODS: Four hundred seventy consecutive eyes of patients who had PRK for the treatment of myopia without astigmatic keratotomy, PRK reoperation, or other surgical procedures were evaluated in a retrospective clinical study. PRK was performed using the Summit Apex excimer laser with attempted corrections from 1 to 7 diopters (D) of myopia. Preoperative and postoperative astigmatism was determined by manifest refraction refined with a 0.25-D Jackson cross cylinder and evaluated with vector analysis. RESULTS: Eighty-five ( 18%) eyes continued to have a spherical refraction after PRK, 53 (11%) eyes had the same preoperative astigmatism, and 332 (71%) eyes had a change in magnitude of astigmatism > or =0.25 D after spherical PRK. The absolute change in astigmatism magnitude irrespective of axis was +0.4 +/- 0.4 (standard deviation) D at 6 months after PRK. Eyes with change in astigmatism power tended to have higher preoperative myopia and higher preoperative astigmatism. Vector analysis revealed surgically induced astigmatism was 0.68 +/- 0.50 D (range, 0-3.25 D) at 1 month and 0.56 +/- 0.47 D (range, 0-3.1 D) at 12 months after spherical PRK. CONCLUSION: Spherical excimer laser PRK is associated with significant surgically induced astigmatism that is likely related to decentration of the ablation, excimer laser beam irregularities, and variations in wound healing across the ablated zone. Surgically induced astigmatism will complicate attempts to correct astigmatism simultaneously at the time of PRK and suggest that such attempts are likely to be problematic for lower levels of astigmatism.     

Treatment of myopia and myopic astigmatism by customized laser in situ keratomileusis based on corneal topography

OBJECTIVE: To evaluate the predictability, efficacy, and safety of customized laser in situ keratomileusis (LASIK) based on corneal topography in myopia and myopic astigmatism. DESIGN: Prospective, noncomparative interventional case series. PARTICIPANTS: One hundred fourteen patients (eyes) with myopia of -1 to -6 diopters (D) and astigmatism of 0 to -4 D (low myopia group), and 89 patients (eyes) with myopia of -6.10 to -12.00 D and astigmatism of 0 to -4.00 D (high myopia group). INTERVENTION: LASIK was performed with the Hansatome Microkeratome and the Keracor 217 spot-scanning excimer laser (Bausch & Lomb Surgical Technolas, Munich, Germany). Individual ablation patterns were calculated on the basis of elevation data obtained with the Orbscan II corneal topography system (Bausch & Lomb Surgical, Irvine, CA). MAIN OUTCOME MEASURES: Manifest spectacle refraction, visual acuity, and change in visual acuity at 3 months after surgery. RESULTS: At 3 months, 51 patients in the low myopia group and 40 patients in the high myopia group were available. In the low (high) myopia group, 96.1% (75.0%) were within +/-0.50 D of emmetropia, and uncorrected visual acuity was 20/20 or better in 82.4% (62.5%), 20/25 or better in 98.0% (70.0%), and 20/40 or better in 100% (95.0%). A loss of two or more lines of spectacle-corrected visual acuity occurred in 3.9% of the low and 5. 0% of the high myopia group. In low myopia, spectacle-corrected visual acuity was 20/12.5 or better in 5.9% preoperatively and in 13.7% at 3 months and 20/15 or better in 37.3% and 47.1%, respectively. Differences were statistically significant. CONCLUSIONS: The customized LASIK based on corneal topography used in this study showed high predictability and efficacy in myopia and myopic astigmatism of -1.00 to -6.00 D, and could possibly improve spectacle-corrected visual acuity in myopia of -1.00 to -6.00 D. Predictability and efficacy were somewhat lower in myopia and myopic astigmatism of -6.10 to -12.00 D. In both groups, a small number of patients lost two or more lines of spectacle-corrected visual acuity.