Confocal microscopy reveals persisting stromal changes after myopic photorefractive keratectomy in zero haze corneas

AIMS—Micromorphological examination of the central cornea in myopic patients 8-43 months after excimer laser photorefractive keratectomy (PRK), using the slit scanning confocal microscope.
METHODS—Patients were selected from a larger cohort of individuals on the basis of full corneal clarity (haze grading 0 to +1; mean 0.3) and their willingness to participate in the study. 15 eyes of 10 patients with myopic PRK (−4 to −11 D; mean 6.7) and an uneventful postoperative interval of 8-43 months (mean 26) were examined. Contact lenses had been worn by eight of the 10 patients for 4-11 years (mean 6.7) before surgery. Controls included the five untreated fellow eyes of PRK patients, 10 healthy, age matched volunteers without a history of ocular inflammation or contact lens wear, and 20 patients who had worn rigid gas permeable (n=10) or soft contact lenses (n=10) for 2-11 years. Subjects were examined with a real time flying slit, scanning confocal microscope using ×25 and ×50 objectives.
RESULTS—In PRK treated patients and contact lens wearers, basal layer epithelial cells sporadically displayed enhanced reflectivity. The subepithelial nerve plexus was observed in all individuals, but was usually less well contrasted in the PRK group, owing to the presence of a very discrete layer of subepithelial scar tissue, which patchily enhanced background reflectivity. Within all layers of the stroma, two distinct types of abnormal reflective bodies were observed in all PRK treated eyes, but in none of the controls. One had the appearance of long (>= 50 µm), slender (2-8 µm in diameter) dimly reflective rods, which sometimes contained bright, punctate, crystal-like inclusions, arranged linearly and at irregular intervals. The other was shorter (<25 µm), more slender in form (<1 µm in diameter), and highly reflective; these so called needles were composed of crystal-like granules in linear array, with an individual appearance similar to the bright punctate inclusions seen in rods, but densely packed. Both of these unusual structures were confined, laterally, to the ablated area, but were otherwise distributed throughout all stromal layers, with a clear predominance in the anterior ones. These rods and needles were observed in all PRK treated corneas, irrespective of previous contact lens wear. On the basis of qualitative inspection, the incidence of rods and needles did not appear to correlate with either the volume of tissue ablated or the length of the postoperative interval. In contact lens wearing controls, highly reflective granules, reminiscent of those from which the needles were composed, were found scattered as isolated entities throughout the entire depth and lateral extent of the corneal stroma, but rods and needles were never encountered. The corneal endothelium exhibited no obvious abnormalities.
CONCLUSION—Confocal microscopy 8-43 months after PRK revealed belated changes in the corneal stroma. These were manifested as two distinct types of abnormal reflective bodies, which had persisted beyond the stage when acute wound healing would have been expected to be complete. The clinical significance of these findings in the context of contrast visual acuity and long term status of the cornea is, as yet, unknown.

Keywords: photorefractive keratectomy; excimer laser; confocal microscopy; stromal pathology     

Response of the cornea for up to four years after photorefractive keratectomy for myopia

PURPOSE: To analyze the long-term corneal topographic changes 4 years after myopic photorefractive keratectomy (PRK). METHODS: This study comprised 15 patients (30 eyes) who had PRK surgery with a scanning-spot excimer laser (Chiron Technolas 217C; Bausch & Lomb, Dornach, Germany) and were followed up to 4 years after surgery. The eyes were subdivided into three groups according to the preoperative spherical equivalent refraction. Corneal topographic maps were obtained for all eyes with a Placido disc topographer. Preoperative and follow-up topographical data were imported into a custom software program, which computed the average composite corneal maps and difference maps for each study group to quantify the anterior corneal changes following laser ablation. The software delineated three concentric zones of the corneal surface to characterize the regional corneal remodeling following the surgery. RESULTS: A significant central corneal steepening (approximately 0.25 D, P < .001) was calculated between the 1- and 4-year postoperative maps in all study groups. A significant steepening (P < .001) of the corneal periphery was also noted for the lower myopic ablations whereas a peripheral flattening (P < .001) was observed for the deeper ablations between 1 and 4 years after surgery. CONCLUSIONS: The anterior corneal surface was observed to remodel for up to 4 years after surface ablation, steepening a mean of approximately 0.25 D.     

Angle kappa changes after photorefractive keratectomy for myopia

The goal of this study was to compare differences in the mean angle kappa and its intercepts before and after photorefractive keratectomy (PRK) for myopia. In a prospective controlled study, myopic patients were treated with aspheric wavefront-guided (personalized) PRK with a Bausch & Lomb Technolas 217z excimer laser. The manifest refraction, visual acuity, and angle kappa were evaluated preoperatively and at 1 and 6 months postoperatively. The same operator performed all angle kappa measurements using Orbscan IIz. A total of 48 cases (96 eyes, 68.75 % female) with a mean age of 26.70 ± 4.89 years (18–34 years) were treated. The preoperative and postoperative mean angle kappa values were not significantly different (4.97 ± 1.24 vs 4.99 ± 1.10 at 6 months). The average horizontal distance (x-intercept) between the visual axis and pupillary axis intersection on the corneal surface measured before surgery (?0.562 ± 0.074 mm) did not significantly differ from the values measured at 1 and 6 months after surgery (?0.559 ± 0.048 and ?0.554 ± 0.055 mm, respectively). Similarly, the average vertical distance (y-intercept) values did not differ before and at 1 and 6 months after surgery (0.156 ± 0.225, 0.142 ± 0.040, and 0.149 ± 0.33 mm, respectively). No differences in the angle kappa or its corneal intercepts were observed between pre- and post-PRK. This finding implies that PRK does not change the corneal vertex locations.     

Confocal microscopy evaluation of stromal ablation depth after myopic laser in situ keratomileusis and photorefractive keratectomy

PURPOSE: To compare the measured ablation depth after myopic laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) with the predicted ablation depth. SETTING: Mayo Clinic, Rochester, Minnesota, USA. METHODS: Twenty-five eyes of 15 patients had PRK and 25 eyes of 15 patients had LASIK to correct refractive errors between -1.50 diopters (D) and -11.00 D. The corneas were examined by in vivo confocal microscopy before and 1 month after both procedures. Thickness measurements were obtained from digital-image analysis of confocal scans. The measured ablation depth, an estimate of the actual photoablation depth, was obtained as the surgically induced stromal thinning between the preoperative and the 1-month post-PRK or post-LASIK central stromal thickness. The predicted ablation depth was recorded from the laser's software program. RESULTS: In LASIK, the measured ablation depth (81 microm +/- 34 [SD]) was 25% greater than the predicted ablation depth (65 +/- 13 microm, P =.007) and the difference between the measured and predicted ablation depths was positively associated with the mean ablation depth (r = 0.81, P<.001). In PRK, there was no difference between the measured ablation depth (48 +/- 19 microm) and the predicted ablation depth (47 +/- 18 microm, P =.84). CONCLUSION: Significantly more tissue than predicted was removed by LASIK than by PRK excimer photoablation with the laser system used in this study.     

Correlation between refractive and corneal topographic changes after photorefractive keratectomy for myopia

PURPOSE: To compare videokeratographic and refractive data obtained before and after photorefractive keratectomy (PRK) for myopia. METHODS: Seventy-four eyes underwent PRK for myopia ranging from -2.50 to -17.00 D (mean, -7.76 +/- 3.17 D). All patients had videokeratography with the EyeSys instrument before, and 1 and 6 months after PRK, and the changes in three corneal power measurements (center of the ablation, apex, and effective refractive power) were compared with refractive changes. RESULTS: Changes obtained in the three corneal power measurements at 1 and 6 months were well correlated with manifest refraction (Pearson's coefficient ranged from 0.71 to 0.84). CONCLUSION: Power measurements obtained with corneal topography, as described above, are a reliable and objective method for the evaluation and follow-up of PRK, provided addition of an approximate 25% correcting factor.     

LASIK术后早期角膜上皮改变的共焦显微镜观察

目的 评价LASIK术后不同时间角膜中央上皮厚度变化，探讨上皮厚度变化与屈光状态之间的关系。方法 设计自身配对研究。选择2002年11月29日至2003年1月24日于天津医科大学眼科中心屈光手术门诊进行原位角膜磨镶术病例24例(48眼)，分别在术前、术后第1、3、7、10、30、60、90天，观察屈光状态的变化，应用活体共聚焦显微镜(Confoscan 3．0)测量中央角膜上皮厚度，并对上皮厚度变化与屈光状态的相关性进行分析。结果 与术前相比，LASIK术后角膜上皮厚度平均增加了10．7％。等效球镜度数变化与上皮厚度的变化呈正相关(r=0．538，P=0．047)。结论 LASIK术后角膜上皮厚度增加，上皮参与了早期角膜组织修复的过程。术后屈光状态变化与上皮厚度的增减有关。     

放射状角膜切开术矫正准分子激光角膜切削术后残余近视

目的 评价放射状角膜切开术（ＲＫ）矫正准分子激光角膜切削术（ＰＲＫ）后残余近视的安全性、有效性及有关并发症。方法 分析１０例病人１４只眼用ＲＫ手术矫正ＰＲＫ后残余近视的屈光及视力变化。ＲＫ后最短观察时间６个月。结果 ３只眼（２１％）接受１次ＰＲＫ治疗,７只眼（５０％）接受２次ＰＲＫ治疗,４只眼（２９％）接受３次ＰＲＫ治疗。１１只眼（７９％）接受４刀Ｒ人眼（２１％）接受８刀ＲＫ术。所有病人ＲＫ术后裸     

Changes in mesopic vision after photorefractive keratectomy for myopia

PURPOSE: To evaluate the mesopic functions of excimer laser treated eyes with different treatment diameters and different laser beam delivery systems. METHODS: In Group 1, 38 eyes were treated with the Aesculap Meditec MEL 60 ArF scanning laser beam excimer laser. The treatment diameter was 5.0 mm. In Group 2, 38 eyes were treated with the Aesculap Meditec MEL 70(G-Scan) flying spot excimer laser; the chosen treatment diameter was 6.5 mm. In Group 3, there were 38 eyes with no treatment; vision was corrected only with spectacles (control group). All eyes had 20/20 best spectacle-corrected visual acuity before surgery, as did the control group. Measurements were carried out preoperatively and at 12 months following surgery. All eyes exhibited normal corneal wound healing, and subepithelial haze was <0.5 according to Hanna's scale. Mesopic functions (mesopic vision and glare sensitivity) were tested with the Mesoptometer II. RESULTS: The average preoperative refractive error in Group 1 was -3.40 D; in Group 2, -3.38 D; in Group 3, -3.44 D. In Group 1, 34% of the treated eyes met the night driving requirements (recognition at 1:5 contrast level), whereas in Group 2, 85%, and in Group 3, 95% of the eyes fulfilled this criteria. When contrast vision was tested under glare conditions in Group 1, 31.6%; in Group 2, 80%; and in Group 3, 94.7% of the eyes identified the target orientation (Landolt ring) at contrast level 1:5. CONCLUSIONS: The unoperated spectacle wearers had better results in all tested functions. The larger 6.5-mm treatment diameter with the use of the flying spot laser beam delivery system resulted in better mesopic function and contrast vision under mesopic conditions than the smaller 5.0-mm diameter.     

Comparison of laser epithelial keratomileusis and photorefractive keratectomy for low to moderate myopia

PURPOSE: To compare the effectiveness, safety, and stability of laser epithelial keratomileusis (LASEK), a modified photorefractive keratectomy (PRK) technique, with those of conventional PRK for low to moderate myopia. SETTING: Department of Ophthalmology, Yonsei University School of Medicine, Seoul, Korea. METHODS: In this prospective study, 27 patients with a manifest refraction of -3.00 to -6.50 diopters were treated and followed for 3 months. In each case, PRK was performed in 1 eye and LASEK in the other eye. The first eye treated and the surgical method used in the first eye were randomized. Postoperative pain, epithelial healing time, uncorrected visual acuity (UCVA), manifest refraction, corneal haze, and surgical preference were examined in PRK- and LASEK-treated eyes. RESULTS: During the 3 month follow-up, there were no significant between-eye differences in epithelial healing time, UCVA, or refractive error. However, LASEK-treated eyes had lower postoperative pain scores (P =.047) and corneal haze scores (1 month; P =.02) than PRK-treated eyes. Seventeen patients (63%) preferred the LASEK procedure. CONCLUSIONS: Laser epithelial keratomileusis safely and effectively treated eyes with low to moderate myopia. It reduced the incidence of significant postoperative pain and corneal haze and may prevent the flap- and interface-related problems of laser in situ keratomileusis.     

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.     

LASEK and photorefractive keratectomy for myopia: clinical and confocal microscopy comparison

PURPOSE: To compare postoperative visual acuity and corneal morphology after laser epithelial keratomileusis (LASEK) versus photorefractive keratectomy (PRK) in the correction of low to moderate myopia. METHODS: In a double-blind, randomized clinical trial, 50 myopic patients (mean: -4.5 +/- 1.35 diopters) were randomized to receive LASEK in one eye and PRK in the fellow eye. No mitomycin C eye drops were used in this study. Patients were observed daily for 4 days, then at 1 month and every 3 months up to 1 year. Uncorrected and best-corrected visual acuity (UCVA and BSCVA), manifest refraction, corneal epithelium healing time, postoperative pain, and corneal haze were evaluated. Corneal wound healing was quantified with corneal confocal microscopy. RESULTS: Refractive error, UCVA, and BSCVA were not statistically different between eyes treated with LASEK and PRK. Corneal epithelium healing time was 2.52 +/- 0.99 days in the eyes treated with PRK and 2.29 +/- 0.52 days in the eyes treated with LASEK (P=.22). The postoperative pain score was 2.17 +/- 0.87 in the eyes treated with PRK and 2.62 +/- 0.60 (P=.02) in the eyes treated with LASEK. Corneal confocal microscopy showed fewer stromal activated keratocytes and less extracellular matrix deposition in the eyes treated with LASEK than in the eyes treated with PRK at 1 month postoperatively (P=.003). CONCLUSIONS: LASEK is an effective and safe procedure for low to moderate myopia, but it seems more painful until full corneal reepithelization. In the early postoperative period, the corneal wound healing process is significantly less intense in eyes treated with LASEK than in eyes treated with PRK. The role of LASEK in corneal wound healing modulation remains controversial.     

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.     

PRK治疗近视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 (photorefractive keratectom y,PRK )治疗近视术后角膜表面形态及偏中心切削。方法　 76例 (1 5 0只眼 )行 PRK,术前屈光度 (- 3.0 0～ - 1 0 .0 0 ) D,平均 (- 6 .0 8± 1 .2 1 ) D。术后 1、3、6、1 2个月行角膜地形图检查。结果　角膜地形图形态分为平滑型、半圆型、钥匙孔型、肾型、中央岛型和不规则型 6种。角膜地形图形态有逐渐变平滑的趋势。术后 3个月以后 ,各种类型所占比例基本稳定。平滑型术后裸眼视力较好。偏中心距离 >0 .5 0 m m时 ,术后视力恢复不良。结论　角膜地形图分析系统能精确测量、分析全角膜的前表面形态 ,观察术后效果、指导手术设计 ,从而提高 PRK治疗近视的准确性、安全性和预测性     

近视眼准分子激光角膜切削术后的对比敏感度评价

目的:评价近视患者PRK术后的对比敏感度变化.方法:应用CSV-1000E图表对41例接受Nidek EC-5000型准分子激光仪行PRK手术的患者,行单眼对比敏感度测量.患者术前平均屈光度为-2.62±1.33D(范围从-0.75至-4.00D).应用CSV-1000E对比敏感度仪分别在术前,术后1wk;1,3,6mo行对比敏感度检查.结果:将每个空间频率的对比敏感度对数值进行统计学分析,并应用图表与正常值进行比较.结果显示对比敏感度在术后1wk及术后1 mo时明显降低,从第1 mo开始,对比敏感度尤其是低空间频率的对比敏感度快速恢复,在第3mo,只有6和12cpd两种空间频率的对比敏感度明显降低,在术后6mo时,所有频率的对比敏感度功能都明显增加.结论:PRK术后患者第1 mo对比敏感度功能明显降低,但在术后6mo时对比敏感度功能即恢复至术前水平.     

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。