Elsevier

Ophthalmology

Volume 108, Issue 1, January 2001, Pages 112-120
Ophthalmology

Corneal haze after photorefractive keratectomy using different epithelial removal techniques1: Mechanical debridement versus laser scrape,

https://doi.org/10.1016/S0161-6420(00)00426-7Get rights and content

Abstract

Purpose

To determine differences of corneal wound healing and haze after photorefractive keratectomy (PRK) using either mechanical epithelial debridement or laser-scrape epithelial removal in human subjects.

Design

A 6-month randomized, masked, prospective, paired-eye clinical study.

Participants

Twenty eyes in 10 myopic patients treated between March 1999 and May 1999.

Intervention

Photorefractive keratectomy treatments with two different epithelial removal techniques. Continuous z-scan of confocal image, termed confocal microscopy through focusing (CMTF), was performed before surgery and at 3 weeks, 6 weeks, 3 months, and 6 months after surgery.

Main outcomes measures

Epithelial and stromal thickness measurement, achieved stromal ablation depth, and objective assessment of corneal light-backscattering (corneal haze) were obtained from digital image analysis of the CMTF scans. Manifest refraction was also measured. Student’s paired t test or two-way repeated-measures analysis of variance after rank transformation were performed to evaluate statistical differences between groups.

Results

Comparison of the mean posttreatment spherical equivalent between the two techniques showed no statistically significant difference. In preoperative corneas, mean epithelial thickness was 50.08 ± 3.70 μm in the mechanical debridement group and 50.49 ± 4.01 μm in laser-scrape group (not significant). For both groups, the epithelium was significantly thinner at 3 weeks, but returned to preoperative values by 6 months, with no difference between groups. Planned stromal ablation depth by PRK was 59.38 ± 11.48 μm (39–73 μm; n = 8) in the mechanical group and 57.75 ± 7.21 μm (48–70 μm; n = 8) in the laser-scrape group. Achieved stromal ablation depth was not significantly different between the two groups. Most importantly, in both groups CMTF-measured corneal haze increased significantly after surgery, peaked at 3 months, and then decreased at 6 months, with no significant difference between groups. (Power = 0.96).

Conclusions

There is no significant difference in the corneal wound healing response between mechanical epithelial debridement versus laser-scrape technique in human myopic eyes undergoing PRK.

Section snippets

Patients

Twenty eyes of 10 patients (seven women, three men; age, 31.5 ± 7 years; range, 22–41 years) were enrolled in this study, and mean spherical equivalent was −4.75 ± 0.94 diopters (D; range, −2.75 to −6.00 D). The surgical candidates were given consent forms regarding excimer laser PRK and the different methods of epithelial removal. In all patients, one eye was treated with mechanical epithelial debridement and the fellow eye was treated using the laser-scrape technique. The research protocol

Morphologic characteristics of anterior stromal wound healing

Differences in anterior stromal wound healing morphologic characteristics were assessed in the same patient before and after PRK performed after laser-scrape epithelial debridement (Fig 1). Anterior stromal images were obtained from the CMTF peak of the anterior keratocyte layer or anterior stromal haze, which were located within 60 μm of the stromal surface. In the preoperative cornea, normal quiescent keratocytes with low-reflecting nuclei were observed (Fig 1A). At 3 weeks after PRK,

Discussion

Mechanical debridement was the first method used for epithelial removal before PRK surgery. Although this technique is quite effective, several problems may occur. The time required for the debridement can be longer than the laser-scrape technique, especially for inexperienced surgeons. This may cause stromal dehydration secondary to evaporation and could affect refractive predictability. Also, Bowman’s layer defects, irregular anterior stromal surface, and retained islands of residual

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    Supported in part by National Eye Institute (grant no.: EY07348 [JVJ] Bethesda, Maryland; and Senior Scientist Awards [JVJ and HDC]) an Olga Keith Weiss Scholar Award [WMP] and an unrestricted grant from Research to Prevent Blindness, Inc., New York, New York.

    1

    The authors have no proprietary interest in any of the equipment mentioned in this article.

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