Epithelial Alterations Following Photorefractive Keratectomy for Myopia

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Abstract
BACKGROUND: A retrospective observational study was conducted to test the hypothesis that there is clinically measurable epithelial hyperplasia after photorefractive keratectomy (PRK), and to determine its effect on the epithelial oxygen uptake rate. METHODS: One hundred myopic eyes who had been previously treated unilaterally with PRK were examined. Fifty eyes were treated with the Summit excimer laser (Summit Technology, Waltham, Mass) 27 ± 7 months previously with ablation zone diameters of 4.1, 4.3, 4.5, or 5.0 mm. Fifty eyes were treated with the VISX excimer laser (VISX Inc, Sunnyvale, Calif) 5 ± 4 months previously with one ablation zone diameter of 6.0 mm. The untreated eyes served as controls. Epithelial thickness was measured at a standardized central area within the ablation zone with a modified optical pachometer. Oxygen uptake rate was measured in a subgroup of 30 eyes (20 Summit and 10 VISX). RESULTS: The epithelium after PRK was 24% thicker than in the control eye in the Summit group (mean difference 13 ± 10 µm; p < .01) and 7% thinner in the VISX group (mean difference - 4 ± 10 µm; p < .01). A higher oxygen uptake rate correlated with a thicker epithelium (r = 0.42; p < .05). CONCLUSIONS: The epithelium was significantly thicker after PRK between 13 and 37 months after treatment with the Summit excimer laser using ablation zone diameters of 4.1 to 5.0 mm. The epithelium was thinner between 1 and 15 months after treatment with the VISX laser using an ablation zone diameter of 6.0 mm. An increase in oxygen uptake rate reflected the metabolic rate of a greater number of cells in the hyperplastic layer. [J Refract Surg. 1995;11:113-118.]