Topography-controlled excimer laser photorefractive keratectomy

PURPOSE: To assess whether photorefractive keratectomy (PRK) controlled by videokeratography can successfully treat refractive errors in eyes with corneal irregularities and improve spectacle-corrected visual acuity. METHODS: In a prospective clinical study, PRK was performed in 10 eyes of 10 patients. Reason for surgery was irregular astigmatism after penetrating keratoplasty, corneal irregularity after corneal scarring, corneal astigmatism in keratoconus, and decentration after myopic and hyperopic PRK. Excimer ablation was controlled by preoperative videokeratography (Orbscan II, Orbtek) using the MEL-70 system from Aesculap Meditec. Follow-up was 6 months. RESULTS: Concerning manifest refraction, the sphere was reduced on average from +1.92 to +0.57 D, 6 months postoperatively. Cylinder changed from -1.95 D on average to -0.30 D at 6 months postoperatively. There was improvement of uncorrected visual acuity of 2 or more lines in 5 eyes and no change in 5 eyes 6 months postoperatively. Spectacle-corrected visual acuity improved in 2 eyes by 2 to 3 lines, in 9 eyes by 1 to 3 lines, and showed no change in 1 eye. CONCLUSION: Videokeratography-controlled PRK improved refractive errors in irregular corneas with improvement of spectacle-corrected visual acuity.     

PRK对压平眼压测量的影响

目的：通过前瞻性研究方案探讨ＰＲＫ手术对压平眼压测量的影响。方法：使用手持ＰＥＲＫＩＮＳ压平眼压计、超声角膜测量仪及角膜曲率测量仪测量ＰＲＫ术前及术后１个月眼压、中央角膜厚度及角膜曲率。结果：ＰＲＫ术后压平眼压、中央角膜厚度及角膜曲率。结果：ＰＲＫ术后压平眼压、中央角膜厚度及角膜曲率均较术前明显降低,眼压的变化与中央角膜厚度的变化直接相关,中央角膜厚度每减少１０βｍ,压平眼压测量值降低１ｍｍＨｇ,     

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     

An introduction to excimer laser photorefractive keratectomy

Laser research has rapidly expanded in the area of corneal sculpting in the past few years. Lasers with specific wavelengths in the ultraviolet and infrared ranges are best suited for ablating corneal tissue without disturbing clarity of the surrounding matrix. This is essential in laser refractive procedures. The excimer laser is an ultraviolet dimer laser with a wavelength of 193 nm. Excimer laser research has progressed rapidly and FDA-approved clinical trials are presently underway. This paper covers various aspects of the excimer's history, qualities of excimer laser ablation, mechanisms of damage, various laser delivery systems, and FDA-approved clinical trial results.     

准分子激光屈光性角膜切削术后角膜地形图分析

目的分析准分子激光屈光性角膜切削术（ｐｈｏｔｏｒｅｆｒａｃｔｉｖｅｋｅｒａｔｅｃｔｏｍｙ,ＰＲＫ）术后角膜切削区的形态、偏心情况和屈光的稳定性。方法对３１２例（３６６只眼）ＰＲＫ手术患者进行术后１、３和６个月的角膜地形图检查。结果术后１个月切削区中心偏离瞳孔中心的距离为０．２６６ｍｍ,双眼平均偏离瞳孔中心的方向均为鼻上侧。切削区形态平滑型占４９．５％,半环型、钥匙洞型、肾型和哑铃型占４２．９％,中心岛型占６．０％。中心岛型对术后最佳矫正视力影响较大。术后１～３个月角膜屈折力变化较大,高度近视比低度近视回退明显。结论提示ＰＲＫ术中瞄准中心问题非常重要,直接影响术后的效果,同时也应长期随访角膜地形图,进一步观察术后的稳定性。     

Bilateral corneal infiltrates after excimer laser photorefractive keratectomy

A 26-year-old man developed painless inferior subepithelial infiltrates away from the site of ablation in both eyes after excimer laser photorefractive keratectomy (PRK) for myopia. Clinical characteristics of the corneal infiltrates resembled staphylococcal-immune infiltrates. The condition responded to treatment with topical diluted steroids and antibiotics. There was no residual corneal scarring. The infiltrates did not affect the refractive outcome of the surgery. Recognition of this rare entity will help clinicians avoid aggressive investigative and treatment modalities that can affect the results of PRK.     

准分子激光屈光性角膜切削术的角膜地形图分析

目的 分析准分子激光屈光性角膜切主后角膜地形图的变化和动态。方法 对接受准分子激光屈光性角膜切削术后随诊３个月的６２例（１２２只眼）和随诊６个月的４９例（９６只眼）的角膜地形图变化和动态进行分析。结果 中央岛型切削是导致术事早期最佳戴镜矫正视力下降１行以上的重要因素，随着时间推移，中央岛型切削逐渐演变其它类型，角膜中央曲率减爱，视力逐步提高。角膜地形图分析，拟似回退指数（ＳｉｍＫ）是反映角膜基质变     

Myopic photorefractive keratectomy with the excimer laser. One-year follow-up

To evaluate the efficacy, predictability, and stability of myopic photorefractive keratectomy (PRK), the authors completed a 1-year follow-up study on a consecutive series of 26 sighted eyes undergoing this procedure. The results of this follow-up are presented. In addition, side effects and complications in another 255 sighted eyes with a follow-up of 3 months to 1 year are reported to judge the safety of the procedure. Twenty-four of 26 eyes (92%) were within +/- 1.0 diopter (D) of the intended final refraction (baseline, -1.4 to -9.25 D). Fifty-eight percent of the eyes were stable within +/- 0.25 D between 6 and 12 months. One year after surgery, none of the patients lost or gained more than one line of best corrected (spectacle) visual acuity. Uncorrected visual acuity improved to 20/40 or better in 96% of the eyes and to 20/20 or better in 48% of the eyes (not including the eyes that were intentionally undercorrected). However, visual acuity with glare decreased from 20/27 preoperatively to 20/31 after 1 year. Scarring occurred in 2.8% of the treated corneas. Risk factors for scarring include noncompliance with postoperative steroid medication, high myopic corrections, and high steroid responders (3.1%). Collagen vascular and other autoimmune diseases are a contraindication for PRK.     

Long-term clinical course of excimer laser photorefractive keratectomy

PURPOSE: Long-term clinical follow-up for 5 years or longer has not yet been reported in Japan. We performed excimer laser photorefractive keratectomy(PRK) on 181 eyes from 1990 to 1993, and 44 of those eyes could be followed for 8 to 10 years. METHODS: The 44 eyes were divided into 3 groups depending on degree of correction. We compared of safety, efficacy, predictability-spherical equivalent, stability, complication, and satisfaction among the 3 groups. RESULTS AND CONCLUSIONS: The first generation PRK was certified clinically to be safe and stable in patients corrected for low to moderate myopia.     

Corneal topography of small-beam tracking excimer laser photorefractive keratectomy.

PURPOSE: To evaluate the topographic characteristic of photorefractive keratectomy (PRK) for low myopia performed with a small-beam (0.9 mm) tracking excimer laser. SETTING: Department of Ophthalmology, LSU Eye Center, Louisiana State University Medical Center School of Medicine in New Orleans, and the Refractive Surgery Center of the South at the Eye, Ear, Nose, & Throat Hospital, New Orleans, Louisiana, USA. METHODS: Sixty-seven eyes of 47 patients had PRK with a small-beam tracking laser. Of these, 49 eyes had data permitting evaluation of ablation centration; usable data for topographic analysis were available for 59 eyes preoperatively, 54 eyes at 1 month, 42 eyes at 3 months, and 25 eyes at 6 months, permitting measurement of various topographic parameters, including the cylinder (CYL), average corneal power (ACP), surface regularity index (SRI), surface asymmetry index (SAI), corneal eccentricity index (CEI), and coefficient of variation of corneal power (CVP). RESULTS: Preoperatively, all eyes were topographically normal. Postoperatively, no eye exhibited a "central island" by even the least-restrictive definition, and all eyes had best spectacle-corrected visual acuities (BSCVAs) of 20/20 or better at all follow-ups. Mean decentration of the ablations from the pupil centers was 0.42 mm +/- 0.28 (SD) (n = 49). There was no correlation between measured decentration and BSCVA (P = .46). The central cornea was flattened (decreased ACP; P < .001) and made oblate (decreased CEI; P < .001) as expected. There was no increase in SRI or SAI (irregular astigmatism) at 6 months compared with preoperative values (P = .91); however, CYL and CVP (varifocality) increased slightly (P = .04 and .02, respectively). CONCLUSION: The absence of significant regular or irregular astigmatism 6 months after PRK with the small-beam laser is an improvement over published results achieved with wide-beam lasers and is consistent with the excellent visual acuity results in this cohort.     

准分子激光角膜切削中心的角膜地形图分析

目的探讨准分子激光角膜切削术（ｐｈｏｔｏｒｅｆｒａｃｔｉｖｅｋｅｒａｔｅｃｔｏｍｙ，ＰＲＫ）的切削中心对视功能的影响。方法采用Ｅｙｅｓｙｓ角膜形态分析系统对随访６个月以上的９８例（１５８只眼）ＰＲＫ前、后１０天的角膜地形图进行分析，确定激光切削中心相对入射瞳孔中心的方向、距离；比较单区和多区域激光切削的偏中心差异。结果切削区中心相对入射瞳孔中心：０～０．５ｍｍ者１００只眼（６３．３％），０．５～１．０ｍｍ者５５只眼（３４．８％），＞１．０ｍｍ者３只眼（１．９％），平均０．４５ｍｍ。多区域切削３８只眼及单区域切削１２０只眼，其偏心量分别为０．５５ｍｍ和０．４４ｍｍ。差异有显著性（ｔ检验，Ｐ＜０．０５）。偏中心切削致术后最好矫正视力下降１～２行者４只眼，其偏心量＞０．５ｍｍ。结论严重的偏心切削将影响术后视功能恢复，术中眼球跟踪系统（ｐａｓｓｉｖｅｅｙｅ－ｔｒａｃｋｉｎｇ，ＰＥＴ）的应用有利于切削中心的确定，减少偏心量。     

Mesopic contrast sensitivity function after excimer laser photorefractive keratectomy

PURPOSE: To evaluate contrast sensitivity under mesopic conditions in patients who had undergone uncomplicated excimer laser photorefractive keratectomy (PRK) for myopia. METHODS: Monocular contrast sensitivity function was measured with the Stereo Optical F.A.C.T. chart in 26 patients who had received PRK using the Nidek EC-5000 excimer laser system. Mean preoperative refractive error was -6.23 +/- 1.69 D (range, -4.00 to -8.25 D); postoperatively, mean refractive error was -0.36 +/- 0.58 D (range, -0.75 to +0.50 D). Contrast sensitivity function was measured 6 months after surgery using four different chart luminances: 85, 5.0, 2.5, and 0.1 cd/m2, the first being a photopic level and the rest mesopic. A control group of eight emmetropic subjects was also studied to allow comparison of results for statistical purposes. RESULTS: Logarithmic values of contrast sensitivity at each spatial frequency were used for statistical analysis and normalized values were used for graphical representation. The results showed a statistically significant reduction (P < .01) in contrast sensitivity for the PRK patients in comparison with the control group under mesopic conditions for each spatial frequency tested (1.5, 3, 6, 12, and 18 c/deg), although no significant contrast sensitivity differences were observed between PRK and control groups at the photopic (85 cd/m2) level (P > .01 for all frequencies). CONCLUSION: Photorefractive keratectomy can induce significant reductions in contrast sensitivity under mesopic conditions, even though the photopic contrast sensitivity function is normal.     

准分子激光角膜屈光性切削术后肿瘤坏死因子︿的表达

目的　探讨准分子激光角膜切削术 (PRK)后肿瘤坏死因子 α(TNF- α)的表达及其对角膜创伤修复的作用。对比 10 g· L- 1 强地松龙和 1g· L- 1 双氯芬酸钠对 TNF- α表达的影响。方法　应用半定量反转录 -多聚酶链式反应 (semi- quantitative,RT- PCR)的方法探测 PRK后兔角膜细胞活性因子不同时间 m RNA表达的变化 ,并在相应时间点观察细胞学改变。结果　 TNF-α在 PRK后 m RNA表达随时间变化 ,表达水平有改变 ,高峰出现在术后 2 4h。10 g· L- 1强地松龙完全抑制 TNF- α的表达 ,双氯芬酸钠无显著影响。结论　在高能量短暂作用的紫外光照射下角膜组织选择性地表达 TNF-α,提示这一细胞因子在PRK后角膜创伤修复过程中有一定作用 ,并证实 10 g· L- 1强地松龙能在转录水平抑制TNF- α的表达     

Corneal infiltrates after excimer laser photorefractive keratectomy and LASIK

PURPOSE: To determine the frequency and clinical characteristics of corneal infiltrates after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) and to evaluate the efficacy of treatment. METHODS: We retrospectively reviewed the records of 8508 eyes treated with PRK or LASIK in a university-based clinic for the correction of refractive errors for 60 days postoperatively. RESULTS: Corneal infiltrates were observed in 35 (0.8%) of 4492 PRK-operated eyes and in 4 (0.1%) of 4016 LASIK-operated eyes. The mean time of diagnosis was 5.46 days. Among the 39 eyes with infiltrates, 10 (9 PRK, 1 LASIK) had culture-verified infectious keratitis. Coagulase-negative Staphylococcus was the most frequently isolated bacterium (50%), followed by S aureus (20%), Corynebacterium xerosis (10%), Streptococcus viridans (10%), and an unidentified gram-positive coccus (10%). Final visual acuity of > or = 20/30, without correction, was achieved in 79.5% of the 39 eyes. CONCLUSIONS: Corneal infiltrates occurred in 0.8% of PRK eyes and 0.1% of LASIK eyes. Bacterial smears were positive for several eyes. In all cases, prompt treatment was responsible for good visual outcome.     

Contrast sensitivity after excimer laser photorefractive keratectomy for myopia

AIM: To evaluate contrast sensitivity in patients who had undergone uncomplicated excimer laser photorefractive keratectomy (PRK) for myopia. · METHODS: Monocular contrast sensitivity function was measured with the CSV-I000E chart in 41 patients who had received PRK by the Nidek EC-5000 excimer laser system. Mean preoperative refractive error was -2.62±1.33 D (range, -0.75 to -4.00 D). Contrast sensitivity function was measured preoperatively, 1week, 1, 3 and 6 months after surgery through the CSV-1000E contrast sensitivity unit (VectorVision). · RESULTS: Logarithmic values of contrast sensitivity at each spatial frequency were used for statistical analysis and normalized values were used for graphical representation. Contrast sensitivity decreased 1 week and 1 month postoperatively. Starting from the first month, there was rapid recovery of contrast sensitivity especially at low spatial frequencies, and at the third month, only at 6 and 12 cycles per degree (cpd) statistically significant decrease was seen. Six months after surgery, there was an increase in contrast sensitivity values at all spatial frequencies. · CONCLUSION: Photorefractive keratectomy can induce significant reductions in contrast sensitivity in the first month after surgery; these values returned to the preopereative values at 6 months after surgery.     

Tono-Pen versus Goldmann tonometry after excimer laser photorefractive keratectomy

PURPOSE: To compare intraocular pressure (IOP) measurements by the Tono-Pen 2 tonometer and Goldmann applanation tonometer (GAT) in post-photorefractive keratectomy (PRK) patients. SETTING: Refractive Surgery Center, Assaf Harofeh Medical Center, Zerifin, Israel. METHODS: In 18 patients, IOP was measured by GAT and then by Tono-Pen 2 tonometer 2 to 18 months following PRK (mean 6.6 months +/- 5.1 [SD]). Photorefractive keratectomy had been performed in 1 eye of each patient; the fellow eyes served as controls. Corneal curvature and thickness were evaluated. Ten of the 18 patients were treated with topical steroids. RESULTS: In the post-PRK eyes, mean GAT IOP was 1.8 +/- 3.1 mm Hg lower than mean Tono-Pen IOP (P = .012); there was no significant IOP difference in the control (fellow) eyes. In steroid-treated post-PRK eyes, mean GAT IOP (12.2 mm Hg) was 2.2 +/- 1.3 mm Hg lower than mean Tono-Pen IOP (14.4 mm Hg) (P = .0007). Mean Tono-Pen IOP in steroid-treated post-PRK eyes was 4.3 +/- 3 mm Hg higher than in the fellow eyes (P = .0014); mean GAT IOP was only 2.3 +/- 3.5 mm Hg higher (P = .04). In post-PRK eyes without topical steroid treatment, mean GAT IOP was 2.0 +/- 1.18 mm Hg lower than in the fellow eyes (P = .001); there was no significant difference in Tono-Pen IOP. There was a negative correlation between the difference in IOP values (Tono-Pen minus GAT) and corneal curvature in post-PRK eyes (r = 0.76, P = .0108, n = 15). CONCLUSIONS: The Tono-Pen tonometer appeared to be less affected than the GAT by the relative flattening, thinning, and anterior stromal decreased rigidity of the central cornea that occur following PRK. Post-PRK steroid-induced IOP elevation may be masked by the artifactual decrease in GAT IOP.