Risk factors of regression and undercorrection in photorefractive keratectomy:a case-control study

AIM:To determine risk factors of regression and undercorrection following photorefractive keratectomy (PRK) in myopia or myopic astigmatism.METHODS: A case-control study was designed in which eyes with an indication for re-treatment (RT) were defined as cases; primary criteria for RT indication, as assessed at least 9mo postoperatively, included an uncorrected distance visual acuity (UDVA) of 20/30 or worse and a stable refraction for more than 3mo. Additional considerations included optical quality symptoms and significant higher order aberrations (HOAs). Controls were chosen from the same cohort of operated eyes which had complete post-operative follow up data beyond 9mo and did not need RT. The cohort included patients who had undergone PRK by the Tissue-Saving (TS) ablation profile of Technolas 217z100 excimer laser (Bausch & Lomb, Rochester, NY, USA). Mitomycin C had been used in all of the primary procedures.RESULTS:We had 70 case eyes and 158 control eyes, and they were comparable in terms of age, sex and follow-up time (P values:0.58, 1.00 and 0.89, respectively). Pre-operative spherical equivalent of more than -5.00 diopter (D), intended optical zone (OZ) diameter of less than 6.00 mm and ocular fixation instability during laser ablation were associated with RT indications (all P values <0.001). These factors maintained their significance in the multiple logistic regression model with odd ratios of 6.12, 6.71 and 7.89, respectively.CONCLUSION:Higher refractive correction (>-5.00 D), smaller OZ (<6.00 mm) and unstable fixation during laser ablation of PRK for myopia and myopic astigmatism were found to be strong predictors of undercorrection and regression.     

准分子激光角膜切削术后的屈光回退

目的通过准分子激光角膜切削术（ｐｈｏｔｏｒｅｆｒａｃｔｉｖｅｋｅｒａｔｅｃｔｏｍｙ,ＰＲＫ）术后屈光回退的分析,以期探讨可能影响回退的因素。方法经ＰＲＫ手术治疗近视于术后发生回退（≥－１．００Ｄ）１０３只眼,术前屈光度－４．００～－１４．５０Ｄ（－８．７５±２．６５Ｄ）。分为二组进行比较,Ⅰ组为中度近视（－４．００～－７．９０Ｄ）,Ⅱ组为高度近视（≥－８．００Ｄ）。结果中度近视回退率１．１７％,高度近视回退率６．９３％（Ｐ＜０．００１）。高年龄组回退率较低年龄组高（Ｐ＜０．０１）。较严重的角膜上皮下雾状混浊（ｈａｚｅ）多与回退伴行。因激素性高眼压减少或停止局部糖皮质激素的应用可导致回退,屈光的稳定性与性别无关,回退常伴Ｋ值增大。结论回退与预期矫正度、年龄以及ｈａｚｅ有明显相关     

Epithelial scrape for photorefractive keratectomy overcorrection associated with induced regression

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

Excimer retreatment for scarring and regression after photorefractive keratectomy for myopia.

AIMS/BACKGROUND--Scarring associated with regression of refractive effect can occur after photorefractive keratectomy (PRK) for myopia. The experience of treating these complications is reported. METHODS--Eighteen of 285 eyes (6.3%) were retreated with the excimer laser. Age, sex, preoperative primary treatment keratometry, pre-primary treatment, pre-retreatment and post-retreatment spherical equivalents, best corrected and uncorrected visual acuities were recorded and analysed. RESULTS--At 6 months post-retreatment, the mean spherical equivalent was -2.07 dioptres (D) (SD 4.60 D). This spherical equivalent persisted in eyes followed for 12 months (-2.85D, SD 4.09 D). Nine of 18 eyes (50%) had uncorrected visual acuity of 6/12 (20/40) or better. If retreatment was undertaken within 6.5 months of the initial PRK, then scarring was likely to recur (p = 0.035). Nine of 10 eyes (90%) which had a retreatment spherical equivalent less than two thirds of their primary treatment spherical equivalent were within plus or minus 1.25D from emmetropia after retreatment. Four of 11 eyes (36%) followed for 12 months after retreatment rescarred with further regression. CONCLUSION--The data showed that eyes with scarring and regression of myopia should not be treated with PRK within 6 months of the initial procedure. Eyes with the highest percentage of regression towards their initial myopia tend to have a poor response to retreatment.     

准分子激光屈光性角膜切削术后兔角膜基质细胞凋亡及其防治的研究

目的：探讨准分子激光屈光性角膜切削术（photorefractive keratectomy,PRK）后凋亡机制介导的角膜创伤愈合反应对屈光度数回退和角膜雾状混浊（haze）的影响,以及局部应用锌制剂的药物效果。方法：对90只新西兰白兔行双眼PRK,将左眼作为实验眼,手术前、后分别给予A组0．1％地塞米松眼液、B组0．5％硫酸锌眼液和C组0．04％丝裂霉素眼液滴眼;右眼作为对照眼。术后定期裂隙灯下观察haze的程度,测量角膜的厚度,进行光镜和透射电镜观察,采用脱氧三磷酸尿苷缺口末端标记法行凋亡细胞检测,并进行对比性分析。结果：（1）PRK术后角膜前基质细胞出现凋亡,实验眼B组凋亡细胞最少（P＜0．01）。（2）术后角膜厚度增加,前基质细胞增多,实验眼haze和增生程度眼B组凋亡细胞最少（P＜0．01）。（3）术后角膜上皮增生,实验眼B组角膜上皮厚度最小（P＜0．01）。结论：PRK术后屈光度数回退和haze的形成是凋亡机制介导的角膜创伤愈合过程,锌制剂可阻止角膜前基质细胞凋亡,最大限度减轻反应性过度增生,有望成为临床防治haze形成和屈光度数回退的理想药物。     

Intraepithelial photorefractive keratectomy for regression after laser in situ keratomileusis.

PurposeTo propose a refractive procedure, intraepithelial photorefractive keratectomy (IE-PRK), to treat regression after laser in situ keratomileusis (LASIK).SettingIMO Instituto de Microcirugı̂a Ocular de Barcelona, Cornea and Refractive Surgery Unit, Autonoma University of Barcelona, Barcelona, Spain; Vall d’Hebron Hospital, Department of Ophthalmology, INSERM, University Hospital, Toulouse, France.MethodsThis open but uncontrolled prospective pilot study assessed the efficacy, predictability, and stability of IE-PRK in 21 eyes of 21 patients who had previous LASIK for myopia or myopic astigmatism with a mean spherical equivalent (SE) refraction of −9.80 diopters ± 2.95 (SD). After LASIK, the eyes regressed to a mean of −1.93 ± 0.82 D. They were retreated with IE-PRK, in which a photoablation was performed directly in the epithelium without damage to Bowman’s membrane. Follow-up was up to 1 year.ResultsEight of the 21 eyes (38%) were emmetropic at 6 months and 11 (52.4%) had a refraction between −0.50 and +0.50 D. Refraction was stable from the second week to the first year, with no significant differences among the mean SEs at 10 days, 6 weeks, and 6 and 12 months.ConclusionThe preliminary results of this small series indicate that IE-PRK appears to be safe, especially in selected cases; 1 line of lost best spectacle-corrected visual acuity occurred in 5% of eyes.     

PRK后视力回退与屈光度的关系

为研究不同屈光度患者准分子激光角膜切削术（ＰＲＫ）后的视力稳定性,对３６１例６１５眼行ＰＲＫ手术并随访６～１８个月,对术后视力回退情况分组统计分析。结果：近视回退率中低度近视组为３．２％,高度近视组为１４．４％,超高度近视组为５６．９％。结论：等值球镜－７．００Ｄ以下的近视患者视力稳定性较好,ＰＲＫ手术应该严格控制手术适应证来减少手术风险     

Repeated phototherapeutic keratectomy (PTK) followed by PTK with photorefractive keratectomy for anterior granular corneal dystrophy

Two preteen siblings with the anterior-stromal variant of granular corneal dystrophy type 1 underwent multiple phototherapeutic keratectomies (PTK) (due to recurrences of the dystrophy) with progressively increasing hyperopia after each procedure. The last procedure performed was an additional photorefractive keratectomy along with the PTK which led to a decrease in the hyperopia with better refractive outcomes. The addition of mitomycin C may have led to a delay in the recurrence of the dystrophy.     

Role of epithelial hyperplasia in regression following photorefractive keratectomy.

AIM--To determine the relation between epithelial hyperplasia and regression of effect after photorefractive keratectomy (PRK). METHODS--Seventy unilaterally treated patients with PRK were examined. All eyes had been treated with the Summit excimer laser 27 (SD 7) months previously with zone diameters of 4.1 to 5.0 mm. The untreated fellow eyes served as controls. Epithelial thickness was measured centrally with a thin slit optical pachometer and manifest subjective refraction was performed. RESULTS--The epithelium was 21% thicker in the treated eye (p < 0.0001). The relation between refractive regression and epithelial hyperplasia was significant (r = 0.41; p < 0.001). CONCLUSIONS--Epithelial hyperplasia after PRK correlated with the myopic shift (including hyperopia reduction) after treatment with the Summit laser. A model is proposed suggesting that both subepithelial and epithelial layers contribute to regression in the Summit treated eyes with 18 microns of epithelial hyperplasia contributing each dioptre of regression.     

Scraping and mitomycin C to treat haze and regression after photorefractive keratectomy for myopia

PURPOSE: To evaluate the efficacy, safety, and predictability of therapeutic scraping and application of a diluted 0.02% mitomycin C solution to treat haze and regression after photorefractive keratectomy (PRK) for myopia. METHODS: We performed a non-comparative, non-randomized retrospective study of 35 eyes of 30 patients who had previously undergone PRK for myopia and developed haze and regression after treatment. The range of refractive error after regression was -0.75 to -5.50 D (mean -2.92 D). Haze, ranging from grade 3 to 4 (scale: 0 to 4) caused a best spectacle-corrected visual acuity loss of 1 to 6 Snellen lines. All eyes were treated 6 to 12 months after PRK by scraping the stromal surface and application of a 0.02% mitomycin C solution for 2 minutes using a soaked merocel sponge. No laser ablation was performed. Corneal transparency, refractive error, and visual outcomes were evaluated over a 12-month follow-up period. RESULTS: All eyes had significant improvement in corneal transparency. Thirty-one eyes had haze grades lower than 1, which were maintained over time. Only four eyes showed haze grades 1 to 2 and two of them needed further treatment using the same technique. At 12 months after treatment, all eyes were within +/-1.50 of original intended correction (mean 0.04 +/- 0.63 D). BSCVA improved in all eyes. No toxic effects were observed during re-epithelialization or during follow-up. CONCLUSION: Single application of diluted mitomycin C 0.02% solution following scraping of the corneal surface was effective and safe in treating haze and regression after PRK.     

多区域准分子激光角膜切削术治疗近视

本文报导了多区域准分子激光角膜切削术治疗近视的疗效。１５０眼随访满６月，中低度近视组（≤－６．０Ｄ）８４眼，高度近视组（－６Ｄ～－１２Ｄ）６６眼。术后半年总体平均裸眼视力达到１．０７±０．２８；１４４眼（９６．０％）最终屈光度在±１．０Ｄ以内，其中中低度近视组８４眼（１００％）、高度近视组６０眼（９０．９％）。术后疗效高于单区域ＰＲＫ文献报导，尤其是高度近视术后稳定性及预测性明显提高     

Phototherapeutic keratectomy for decentration and central islands after photorefractive keratectomy

PURPOSE: To determine visual outcomes after treatment of decentration and central islands occurring after photorefractive keratectomy (PRK). DESIGN: Retrospective, noncomparative case series. PARTICIPANTS: Patients (n = 14) who exhibited decentration or central islands after PRK and photoastigmatic keratectomy (PARK). METHODS: Fourteen eyes with post-PRK decentration (group I) or central islands (group II) were treated by transepithelial phototherapeutic keratectomy guided by epithelial fluorescence without modulating agents, and subsequently were treated with PRK or PARK. Mean follow-up time was 9 months (range, 45 days-21 months). MAIN OUTCOME MEASURES: We analyzed pre- and postoperative keratometry, refractive errors, uncorrected visual acuity (UCVA), best-corrected visual acuity, and haze. In group I, we also measured pre- and postoperative decentration; in group II, we compared pre- and postoperative central island power. RESULTS: Group I showed improvement in centration (P = 0.003). Group II showed decreased central island power (P = 0.18). -LogMAR UCVA improved from 0.59 (20/80(+1)) to 0.17 (20/30) (P = 0.03) and from 0.74 (20/100(-1)) to 0.21 (20/30(-1)) (P = 0.01) after retreatment of groups I and II, respectively. CONCLUSIONS: Retreatment of patients having decentration and central islands after PRK results in improved visual outcomes.     

Late-onset corneal haze and myopic regression after photorefractive keratectomy (PRK)

OBJECTIVE: To report the incidence and clinical course of a series of patients who developed both delayed-onset, clinically significant progressive haze and myopic regression after photorefractive keratectomy (PRK). METHODS: In this retrospective case series, the charts of 542 consecutive patients who had undergone PRK with the VISX Star Excimer or Nidek EC-5000 laser between July 1996 and October 1998 and who had a minimum of 6 months of follow-up were reviewed. Ten eyes of 8 patients developed progressive haze to greater than 1+ and myopic regression equal to or more than -1 D 3 months or more after PRK. The historical and clinical features were reviewed. RESULTS: The incidence of combined progressive haze and myopic regression was 1.8%. The average age was 40.5 years. Three of the 8 patients were female. The median spherical equivalent (SE) attempted correction was -6.69 D (range -4.00 to -12.25 D). Five patients who underwent bilateral PRK had unilateral involvement. The mean SE regression was -2.01 +/- 0.79 D (range -1.00 to -3.00 D). Regression plateaued at a mean of 9.8 months. Haze ranging up to 4+ peaked at a mean of 7.4 months. Topical steroid treatment and/or epithelial scraping was attempted in 3 eyes but was ineffective. CONCLUSIONS: Combined delayed-onset progressive haze and myopic regression can occur after PRK. In such cases, the amount of haze appears to correlate with the magnitude of attempted initial correction (r = 0.639, P = 0.046) although not with the magnitude of subsequent regression. Patients may need at least 10 months of follow-up to achieve a stable refraction and level of haze. These observations suggest a need for improved understanding of corneal wound healing following PRK and of biologic factors that may contribute to variability in outcomes.     

准分子激光角膜切削术矫正RK术后近视22例

目的:探讨准分子激光角膜切削术(PRK)矫正角膜放射状切开术(RK)后残留近视及近视散光的有效性和安全性。方法:应用波长193nm的ArF准分子激光对22例39眼RK术后残留的近视及近视散光进行准分子激光屈光手术治疗。结果:随访5a,平均屈光度由术前-4.21±1.42D下降至术后的-0.41±0.31D,34眼≥术前最佳矫正视力,术前裸眼视力≥1.0者32眼,术后裸眼视力≥1.0者30眼,回退4眼(10%),回退度数<-1.25D。术前矫正视力≤0.9者,术后5a时仅2眼裸眼视力≥1.0。结论:PRK是一种有效和安全的矫正RK术后残留近视的方法。     

Correlation of subepithelial haze and refractive regression 1 month after photorefractive keratectomy for myopia.

PURPOSE: To relate myopic regression after photorefractive keratectomy (PRK) to subepithelial haze at the first postoperative month. METHODS: One hundred nineteen eyes of 119 patients underwent excimer laser PRK for treatment of myopia up to -8.00 D. Eyes were examined at 1, 3, 6, 9, and 12 months after surgery. All eyes received fluorometholone 0.1% for the first 5 postoperative months in a tapered dose. Dexamethasone 0.1% qid for 1 month was prescribed to all eyes with a spherical equivalent refraction less than plano, followed by an augmented dose of fluorometholone 0.1%. Eyes with myopia greater than -0.75 D at 12 months, as well as those that had received dexamethasone at any postoperative interval--regardless of refractive outcome--were considered to be regressed. Eyes that regressed and those that did not regress were compared statistically (Chi-squared statistical criterion with Yate's correction) regarding haze grade. RESULTS: Forty-seven percent (56 of 119) of eyes regressed. In 89.28% (50 of 56) of eyes, subepithelial haze grade was 1 to 2, and in 10.71% (6 of 56), subepithelial haze was graded 0 to 0.5 at 1 month. Fifty-three percent of eyes (63 of 119) did not regress and in all, subepithelial haze was graded 0 to 0.5 at the first month. The correlation between regression and haze grade 1 or more at the first postoperative month was statistically significant (P<.001). CONCLUSION: Mild to marked subepithelial haze (grade 1 to 2) at the first postoperative month after PRK for myopia is strongly related to regression of initial refractive effect and increasing myopia.     

The epithelial flap for photorefractive keratectomy

BACKGROUND/AIMS: Epithelial debridement for photorefractive keratectomy (PRK) is associated with pain, slower visual recovery, and may be aetiological in haze production. The aim of this study was to assess the clinical results of a new technique involving raising and replacing of an epithelial flap in photorefractive keratectomy. METHODS: A prospective, non-randomised, comparative, paired eye trial was performed in 72 eyes of 36 patients who underwent PRK with a Nidek EC-5000 excimer laser. For epithelial debridement before PRK, the eyes were divided into two groups. The first eye of each patient was treated with 20% ethanol debridement and the second eye with an epithelial flap which was replaced after treatment. PRK was carried out with the same laser and nomogram in both groups by the same surgeon. Visual and refractive outcome of PRK treatment was compared in both groups. RESULTS: The mean (SD) preoperative mean spherical equivalent (MSE) was -3.61 (1.38) dioptres (D) (range -1.00 D to -7.88 D) with no significant difference between the two groups. After a mean follow up period of 62.6 weeks (range 52-70) the final MSE was +0.07 (0.61) D (range -5.50 D to +4.50 D) in the debridement group and -0.24 (0.43) D in the epithelial flap group. There was no statistically significant difference between the two groups in postoperative MSE. The best corrected visual acuity was better in the epithelial flap group at all visits; this difference was statistically significant (p<0.05). The corneal haze was less in the epithelial flap group and this difference was also statistically significant (p<0.05). CONCLUSIONS: Managing the corneal epithelium as a hinged flap with 20% ethanol is a safe technique with faster visual rehabilitation and reduced haze compared with debridement of the epithelium with alcohol. Further studies need to be performed to compare pain levels postoperatively with the epithelial flap and epithelial debridement.     

准分子激光角膜切削术治疗近视的并发症

为分析准分子激光角膜切削术（ＰＲＫ）治疗近视的并发症，对１３９例（２５７眼）ＰＲＫ术后随访半年至一年。结果表明：术后一年，低中度和高度组各有１眼最佳矫正视力丢失二行，分别占２．５％和３．３％；低中度和高度组的角膜上皮下１级混浊分别为１０．８１％和１５．１６％，２级混浊分别为２．７３％和０％；激素性高眼压，在发生率最高的３个月时，可分别达２４．３７％和２５．３２％，但这种反应性的眼压升高只是暂时的，容易控制；过矫和散光增加的发生率均较低，主要与术者的经验有关。随着术者经验的提高、手术设计的完善及术后用药的研究，这些并发症会降到最低水平。ＰＲＫ是安全、有效的。     

Excimer laser photorefractive keratectomy for hyperopia

BACKGROUND AND OBJECTIVE: Photorefractive keratectomy (PRK) has been extensively evaluated for the correction of myopia. This study was undertaken to assess the safety, efficacy, and reliability of PRK in the correction of hyperopia. PATIENTS AND METHODS: There were 28 eyes with refractions of +1 to +7.75 D treated for hyperopia with the Chiron Technolas 217-C excimer laser. Thorough visual assessments were made before treatment and at regular follow-up to 18 months. Complications and patient satisfaction were noted. RESULTS: At 18 months the mean subjective refraction was +0.46+/-1.00 D with 26 eyes (92.8%) within 1 D of emmetropia. Thirteen eyes (46.4%) achieved uncorrected visual acuity (UCVA) of 20/20 or better and all patients had an UCVA of > or = 20/32 or better. Best corrected visual acuity (BCVA) remained unchanged in 26 eyes (92.8%) and improved in 2 eyes (7.2%). On the seventh day from treatment, 17 eyes (25%) had a loss of 2 or more lines of BCVA. At 15 days this was reduced to 8 eyes (14.3%) and at one month to 3 eyes (3.6%). There were no cases of loss of 2 or more lines of BCVA at 18 months of follow-up. All patients expressed a high degree of satisfaction. CONCLUSIONS: Photorefractive keratectomy safely and effectively reduced hyperopia in the patients studied. The technique was reliable and still offered good results at 18 months of follow-up.