Epithelial thickness profile changes induced by myopic LASIK as measured by Artemis very high-frequency digital ultrasound.

PURPOSE: To characterize changes in the corneal epithelial thickness profile induced by myopic LASIK.
METHODS: This was a prospective study of 37 eyes of 19 myopic LASIK patients. Eyes were divided into three groups according to sphere in the maximum myopic meridian: low (-1.00 to -4.00 diopters [D]), moderate (-4.25 to -6.00 D), and high myopia (-6.25 to -13.50 D). The epithelial thickness profile was measured by prototype Artemis very high-frequency (VHF) digital ultrasound scanner (ArcScan Inc) across the central 10-mm corneal diameter preoperatively and between 3 and 6 months postoperatively. The epithelial thickness profile was determined by averaging the epithelial thickness within annular bands centered on the corneal vertex. The change in epithelial thickness profile was calculated as the difference between the preoperative and postoperative epithelial thickness profiles.
RESULTS: The corneal epithelium thickened after myopic LASIK across the central 6 mm with maximum thickening centrally and progressively less thickening centrifugally in low myopia, and a more homogenous thickening in moderate and high myopia within the 5-mm diameter. The mean epithelial thickening at the corneal vertex was 7.41 +/- 1.09 microm, 9.29 +/- 1.22 microm, and 12.33 +/- 1.05 microm for low, moderate, and high myopia, respectively. The rate of epithelial thickening at the corneal vertex per diopter of myopia treated decreased with increasing myopia.
CONCLUSIONS: Although the magnitude of epithelial thickening increased with increasing ablation depth, in accordance with Barraquer's Law of Thicknesses, the myopic refractive shift due to epithelial thickness profile changes was paradoxically more significant in low myopia than in high myopia.