The role of corneal epithelium in smoothing laser – induced surface irregularities in rabbits.

Abstract

Abstract: : Purpose: The purpose of this study was to develop a mathematical model of the smoothing function of corneal epithelium based on experimental data. Methods: Extended irregularities were created on the corneal surface of fourteen eyes of seven adult pigmented rabbits by means of 100µm deep excimer laser ablations through slits of different widths. One eye of each rabbit received vertical slit ablation while the fellow eye received horizontal to identify possible anisotropy. Reepithelialization was complete within six days after treatment in all eyes examined. Four animals were sacrificed at 3 months while two animals at 6 months postoperatively. Excised corneas underwent histological preparation and evaluation. Histological images were digitized using fixed magnification and the shapes of the corneal substrate as well as of the anterior epithelial surface were identified. The prolonged shape of the irregularities justified the one–dimensional mathematical treatment of the problem. Fourier spectra of both the substrates and the corresponding epithelial surfaces were calculated. Animals enrolled in this study were treated and euthanatized in accordance to the ARVO Statement for the Use of Animals in Ophthalmic and Visual Research, during all phases of the experimental work. Study design involving bilateral treatments was made on the basis of anticipated minor visual impact resulting from the performed procedure in combination with the possible high inter–subject variability of the response. Results: Epithelium layer was thinner at the locations where the substrate featured peaks and thicker over valleys. The corresponding anterior surface of the epithelium appeared smoother than the corresponding corneal substrate indicating a high spatial frequency rejection process. The frequency response of this filtering function, was calculated by Fourier analysis of the anterior epithelium and underlying corneal surface geometries. Conclusions: The smoothing function of epithelium can be modeled as a low–pass filter having different characteristics across the vertical and horizontal directions. This anisotropy of the smoothing function could be attributed to the direction of lid movement.

Keywords: cornea: epithelium • wound healing • refractive surgery