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.     

Wavefront-guided photorefractive keratectomy for myopia and myopic astigmatism

PURPOSE: To evaluate the results of wavefront-supported customized ablation (WASCA) in eyes treated with photorefractive keratectomy (PRK) to correct spherical myopia and myopic astigmatism. METHODS: One-hundred fifty eyes of 104 patients (mean age 33.4 +/- 4.4 years) were included in the study. An Asclepion Shack-Hartmann wavefront aberrometer was used to assess lower and higher order refractive aberrations of eyes, and customized PRK treatments were carried out using the Asclepion-Meditec MEL 70 G-Scan excimer laser. Follow-up time was 6 months. RESULTS: The mean preoperative spherical equivalent refraction was -4.02 +/- -1.04 D, and mean uncorrected visual acuity (UCVA) was 0.06 +/- 0.02. Postoperatively, mean UCVA was 1.04 (better than 20/20), mean best spectacle-corrected visual acuity was 1.22 (20/16), and average spherical equivalent refraction was -0.12 D; 98.6% (148 of 150 eyes) were within +/-0.50 D of intended refraction, and 100% were within +/-1.00 D. Concerning safety, in 71.1% of eyes (107 of 150) BSCVA was the same as preoperatively, and in 8.2% (11 of 150) it increased by two or more Snellen lines. None of the eyes lost two or more lines of BSCVA. The root mean square value for higher order aberrations increased 1.4 times following PRK. CONCLUSIONS: WASCA-guided PRK was efficacious, safe and predictable; BSCVA may be improved by the WASCA method compared to results achievable with a traditional PRK technique, in spite of an increase in the root mean square value for higher-order aberrations.     

Surgically induced astigmatism after photorefractive keratectomy and laser in situ keratomileusis. Summit PRK-LASIK Study Group

PURPOSE: To compare the axis and magnitude of surgically induced astigmatism in photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). SETTING: Multicenter clinical trial. METHODS: In this prospective randomized trial, 220 eyes of 220 patients entered the study cohort: 105 randomized to PRK and 115 to LASIK. All patients received a single-pass, multizone excimer laser ablation as part of a PRK or LASIK procedure. Attempted corrections ranged from -6.00 to -15.00 diopters (D). The LASIK procedures were performed with nasal hinges. Absolute changes in astigmatism and axis and magnitude of surgically induced astigmatism were analyzed. Patients were followed for up to 6 month. RESULTS: In the PRK group, the mean change in absolute astigmatism was +0.14, +0.16 and +0.32 D at 1, 3, and 6 months, respectively; in the LASIK group, the mean change was -0.15, -0.08, and -0.03 D, respectively. At all time points, a greater proportion of PRK than LASIK eyes had an increase in absolute magnitude of astigmatism. In the PRK group, the axis of vectoral-induced astigmatism was significantly different from random at 3 and 6 months (P = .01, P < .001), respectively) with a tendency for induced with-the-rule shifts postoperatively. In the LASIK group, the axis of vectoral-induced astigmatism was significantly different from random at only 1 month (P = .04), and there was no preponderant direction of axis shift. Despite these findings, other analyses showed no statistically significant between-group differences in vectoral axis or magnitude of surgically induced astigmatism. CONCLUSIONS: Induced astigmatism was generally less and more random in axis in LASIK than in PRK; a general trend for induced with-the-rule astigmatism in PRK was not seen in LASIK. Hypothetically, the lamellar corneal flap in LASIK may counteract the tendency toward steepening at 90 degrees seen in PRK by retracting toward the hinge, by masking underlying induced astigmatism in the ablation zone, or by its mitigating influence on postoperative corneal healing.     

Correlation among refractive, keratometric and topographic astigmatism after myopic photorefractive keratectomy

BACKGROUND: Photorefrative keratectomy can be used to flatten the curvature of the anterior cornea and reduce the myopic refraction of the eye. This leads to unphysiological topographical changes of the cornea and may alter the conditions for examinations of corneal surface topography. The purpose of this study was to check for mutual agreement of three different methods of assessment of astigmatism before and after myopic photorefractive keratectomy (PRK). PATIENTS AND METHODS: Forty-seven eyes of 28 patients (age 32.7+/-6.6 years) following PRK using an 193-nm excimer laser were included in this study. 37 eyes were treated for pure myopia (-4.9+/-2.4 D) and 10 eyes for myopic astigmatism (sphere -2.0 to -7.0 D, cylinder -1.0 to -3.0 D). Preoperatively and at 18 months postoperatively, subjective refractometry, keratometry and topography analysis were performed. The axes of topographic and keratometric cylinder were standardized periodically (180 degrees) with respect to the refractive cylinder axis. RESULTS: Pre- and postoperatively, the absolute astigmatism values correlated highly significantly between all three methods (P< or =0.001). The mean refractive cylinder was 0.65+/-0.61 D preoperatively and 0.46+/-0.41 D postoperatively (P=0.2). The mean keratometric astigmatism was 1.14+/-0.64 D before and 0.94+/-0.50 D after PRK treatment (P=0.2). Among the three methods, the mean topographic astigmatism was the highest (P<0.001) preoperatively (1.31+/-0.56 D) and postoperatively (1.21+/-0.52 D) (P=0.3). In eyes treated for pure myopia, no difference between pre- and postoperative refractive, keratometric and topographic astigmatism was detected (P>0.5). The axes of both topographic and keratometric astigmatism correlated highly significantly with the refractive cylinder axis (R> or =30.9, P<0.0001). CONCLUSION: Up to 2 years after myopic PRK, the difference between refractive and keratometric astigmatism does not differ from the preoperative value, indicating an even corneal surface. The absolute astigmatism values and the cylinder axis correlated well between subjective and objective methods of astigmatism assessment. Thus, objective measurements may be helpful in determining the cylinder component of best spectacle correction after PRK. However, topographic analysis overestimates astigmatism values systematically before and after PRK.     

准分子激光角膜切削术治疗近视及近视散光远期疗效观察

目的:评价准分子激光角膜切削术治疗近视、近视散光的远期疗效,分析术后远期视力回退的相关因素。方法:测量、比较79例(137眼)不同程度的近视及近视散光患者PRK术后1和7a的视力、屈光度、角膜屈光力、角膜厚度、角膜Haze变化,并对术后视力回退的影响因素进行分析及回归分析。结果:术后7a视力、屈光度与术后1a比较差异均有显著意义(P <0.05);术后不同时期屈光度低组与高组比较视力及屈光度差异均有非常显著意义(P <0.01)。角膜厚度术后7a较术后1a差异有非常显著意义(P <0.01),角膜屈光力差异无显著意义(P >0.05)。术后裸眼视力回退(Y)与术后等效球镜屈光度变化(X)呈正相关(r =0.49,P <0.01),与术前球镜屈光度呈负相关(r =-0.20,P <0.05),建立多元逐步回归方程为:Y =0.08 0.12X。结论:PRK术后远期视力及屈光度均有轻度回退,以高度近视眼明显,影响术后远期视力回退的主要因素是术后屈光度的变化。     

准分子激光角膜切削术治疗近视散光的临床分析

目的评价准分子激光屈光性角膜切削术（ｐｈｏｔｏｒｅｆｒａｃｔｉｖｅｋｅｒａｔｅｃｔｏｍｙ，ＰＲＫ）矫正近视性角膜散光的结果。方法对２３１例（３８７只眼）近视患者按术前散光度分为Ａ（无散光）、Ｂ（散光＜２．００Ｄ）及Ｃ（散光＞２．００Ｄ）三组，并用ＰＲＫ对其近视和散光进行治疗。对手术前、后散光的变化进行比较，采用矢量分析方法，对手术矫正效应的量和方向进行分析。结果Ｂ、Ｃ两组术前散光分别为１．２９±０．４８Ｄ和３．０７±０．７２Ｄ，按术后６个月时残留散光计算，手术矫正效应分别为１．１０±０．６７Ｄ和２．４２±０．９３Ｄ，而手术效应与术前散光轴之间的夹角分别为５．８°±２．１°和４．９°±２．４°。结论ＰＲＫ治疗散光效果明显，轴向准确，但在高度散光组有一定的回退现象。     

Excimer laser photorefractive keratectomy for high myopia and myopic astigmatism.

BACKGROUND AND OBJECTIVE: To determine the efficacy, safety, and predictability of excimer laser photorefractive keratectomy of high myopia and myopic astigmatism. PATIENTS AND METHODS: 76 eyes of 52 patients with myopia from -8.00 to -23.50 diopters (D) with or without astigmatism up to -5.50D were treated with the VISX 20/20 excimer laser (VISK, Santa Clara, CA) and a multi-zone ablation technique. Visual acuity, manifest refraction, corneal haze, and topography were evaluated at 1 week and 1, 3, 6, 12, and 18 months postoperatively. RESULTS: Postoperative refractions were generally stable after 12 months. At the last follow-up all patients were within - 1.96 D of the intended correction. Eighteen months postoperatively, 68% of patients undergoing photorefractive keratectomy (PRK), and 65% of patients undergoing photo astigmatic refractive keratectomy (PARK), were within 1 D of planned refraction. Furthermore, 87% of patients after PRK and 80% of patients after PARK had a visual acuity of 20/40 or better. CONCLUSIONS: High myopia with or without astigmatism was successfully treated in most of the patients using PRK. The stability of the postoperative refraction during the first 18 months seems to be good. The incidence of adverse effects was low but improvements in the future should further reduce complications, thus increasing the safety of refractive procedures.     

Corneal iron ring after hyperopic photorefractive keratectomy.

PURPOSE: To report the incidence and course of corneal iron deposition after hyperopic photorefractive keratectomy (PRK). SETTING: Gazi University, Medical School, Department of Ophthalmology, Ankara, Turkey. METHODS: Between January 1995 and December 1997, 62 eyes had PRK to correct hyperopia. RESULTS: Nine eyes developed corneal iron ring 5 to 8 months (mean 6.25 months +/- 1.3 [SD]) after PRK for hyperopia. The rings persisted during the mean follow-up of 19 +/- 11.09 months. CONCLUSION: The ring-shaped iron deposition after PRK for hyperopia must be differentiated from the Fleischer ring. Our results suggest that the slitlamp findings of peripheral corneal iron deposition in hyperopic PRK patients correlate with achieved correction.     

Changes in measured intraocular pressure after hyperopic photorefractive keratectomy

PURPOSE: To investigate the effect of hyperopic photorefractive keratectomy (PRK) on intraocular pressure (IOP) measurements. SETTING: University of Ottawa Eye Institute, Ottawa Hospital, Ottawa, Canada. METHODS: In this retrospective cohort study, IOP and central corneal thickness (CCT) were measured preoperatively and at 1, 2, 3, 6, 12, 18, and 24 months in 191 eyes that had hyperopic PRK with the VISX Star excimer laser. All corrections applied were between +1.00 and +6.50 diopters (D) of sphere and less than 3.75 D of cylinder. RESULTS: At all postoperative examinations, the mean IOP in the hyperopic PRK group was 1.0 to 1.8 mm Hg lower than the preoperative IOP (P <.001). A large range of IOP changes was found across the population; eg, at 6 months, 49% of the eyes had a change in IOP from baseline of at least +/-3 mm Hg. A mean reduction of 19 microm of CCT was found with pachymetry after surgery (P < .001). The change in IOP readings postoperatively was not correlated with age, sex, keratometric readings, or applied correction. Changes in IOP were strongly correlated with preoperative IOP at all time points and with preoperative CCT at 18 and 24 months (P < .001). After hyperopic PRK, the measured IOP was more likely to increase in patients with preoperative IOPs less than 14.5 mm Hg and more likely to decrease in patients with preoperative IOPs above 14.5 mm Hg. CONCLUSION: Changes in IOP after hyperopic PRK were similar to changes after myopic PRK, despite only minimal changes in the CCT. This suggests that hyperopic PRK results in biomechanical effects that modify the elastic properties of the cornea beyond the changes in rigidity expected from central corneal thinning. There was a strong negative correlation between the measured preoperative IOP and the change in IOP postoperatively that was likely the result of regression of the mean effect.     

准分子激光屈光性角膜切削术后眼压测量值的变化

目的：探讨影响准分子激光屈光性角膜切削术（laser photorefractive keratectomy,PRK)后眼压测量值变化的因素。方法：对209例（364只眼）近视患者行PRK,手术前、后采用Goldemann压平式眼压计测量患者的眼压,并测量角膜厚度和角膜曲率,进行量角膜厚度和角膜曲率,进行统计学分析。术后随访时间＞1年。结果：术后6个月和12个月术眼的眼压测量值低于术前,差异有非常显著意义（P＜0．001）,术后12个月的眼压测量值低于术后6个月,差异有非常显著意义（P＜0．001）,术后12个月的眼压测量值低于术后6个月,差异有非常显著意义（P＜0．001）。术后眼压测量值的降低与角膜厚度的减少和角膜曲率的降低均呈高度正相关（P＜0．01）,其二元回归方程为Y（手术前、后眼压差,mmHg）＝1．156＋0．022X1（手术前、后角膜厚度差,μm)＋0．052X2（手术前、后角膜曲率差,D）。结论：PRK术后眼压测量值低于术前;角膜厚度和角膜曲率是导致手术前、后眼压测量值变化的因素。     

Retinal detachment in myopic eyes after photorefractive keratectomy

PURPOSE: To analyze the incidence and characteristics of retinal detachment (RD) in myopic patients who had photorefractive keratectomy (PRK). SETTING: Universidad Miguel Hernández, Instituto Oftalmológico de Alicante, Alicante, Spain. METHODS: The incidence of RD in 5936 consecutive eyes that had PRK to correct myopia was studied. Mean follow-up was 38.5 months +/- 17.4 (SD). RESULTS: Retinal detachment occurred in 5 eyes (0.08%); 2 in women and 3 in men. The mean interval between PRK and RD was 21. 00 +/- 15.89 months (range 9 to 48 months). The mean best corrected visual acuity (BCVA) after PRK and before RD development was 20/81 (range 20/200 to 20/25). After RD repair, the mean BCVA was 20/460 (range 20/2000 to 20/29). In 4 of the 5 eyes, BCVA after RD was within 1 line of the preoperative value; in 1 eye, it decreased from 20/40 to 20/2000. The mean spherical equivalent (SE) before RD treatment was -1.35 +/- 1.08 diopters (D) (range 0 to -3.00 D) and after RD treatment, -2.95 +/- 0.83 D (range -2.00 to -4.00 D). Differences between SE before and after RD treatment were statistically significant (P =.01, paired Student t test). CONCLUSIONS: The incidence of RD after PRK to correct myopia was 0.08%. In 4 of 5 eyes, there was little or no visual loss; but in the group as a whole, there was a significant increase in myopic SE.     

准分子激光角膜切削术治疗近视和近视散光的临床研究

目的 评价准分子激光角膜切削术矫正近视的结果。方法 我院自１９９６年９月到１９９７年１０月,应用ＳＶＳＡＰＥＸ型（Ｓｕｍｍｉｔ Ｔｅｃｈｎｏｌｏｇｙ Ｉｎｃ．ＵＳＡ）准分子激光治疗仪,对１６８例近视患者（３１６只眼）行ＰＲＫ手术,对其中的１５０例（２６０只眼,占８４％）患者随诊至少３ｍｏ以上,最长１ａ;男６８例（１１６只眼,占４０．１％）,女８２例（１４４只眼,占５９．９％）。１５０例（２６０只眼     

Myopia and myopic astigmatism photorefractive keratectomy: applying an advanced multiple regression-derived nomogram

Graefe's Archive for Clinical and Experimental Ophthalmology - To evaluate a multiple regression-derived nomogram for myopia and myopic astigmatism photorefractive keratectomy (PRK). Regression...