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Corneal haze after photorefractive keratectomy using different epithelial removal techniques: mechanical debridement
Y G Lee1, W Y Chen, W M Petroll
1Department of Ophthalmology, University of Texas, Southwestern Medical Center at Dallas, Dallas, Texas, USA.
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 microm in the mechanical debridement group and 50.49+/-4.01 microm 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 microm (39-73 microm; n = 8) in the mechanical group and 57.75 +/- 7.21 microm (48-70 microm; 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.