Narrow angle light scatter in rabbit corneas after excimer laser surface ablation

Abstract

Corneal haze following excimer laser ablation is an adverse after-effect of photorefractive keratectomy (PRK) and is associated with the development of subepithelial opacities. The present work pertains to the measurement of light scattering in rabbit corneas following excimer laser treatment; to the microscopic analysis of the light-scattering corneal structures; and to the development of a mathematical model of light propagation through the post-laser treatment cornea. Photorefractive keratectomy (PRK-6D, 6 mm optical zone) followed by standard postoperative pharmaceutical treatment was performed on rabbit eyes. Animals were examined clinically on a weekly basis and sacrificed after the tenth postoperative week. Confocal microscope image sequences were acquired immediately before animal sacrifice. After the scatter measurement, the corneas were prepared for histopathological evaluation. The subepithelial structures observed using the confocal microscope correspond to refractive index (and therefore optical path difference (OPD) variation. This OPD distribution can be approximated with a fractal surface, band-pass filtered in the Fourier domain. The angular distribution of scattered light is characterised by a narrow forward peak of the order of 0.5 degrees full-width at half maximum (FWHM) in accordance with the sizes of the subepithelial structures (5-150 microm).The intensity of scattered light is correlated with the thickness of the subepithelial scar-tissue layer.