Epi-LASIK update: overview of techniques and patient management.

摘要

Epi-LASIK allows refractive surgeons another option for separating the corneal epithelium before surface ablation. The evolution of epi-LASIK as a new technique for surface ablation stems from its predecessors photorefractive keratectomy (PRK) and laser subepithelial keratomileusis (LASEK). Past methods of removing epithelial cells in PRK involved mechanical debridement, use of a rotating brush, and laser transepithelial ablation. The debridement of corneal epithelium involves postoperative pain while the cornea heals. LASEK uses 20% alcohol to loosen the epithelium from its stromal bed. After 25 seconds, the epithelium is lifted off of the surface and reflected back before excimer ablation. In a study conducted by Azar et al,2 the question of safety in regards to the use of alcohol on epithelial cell viability was examined. Once alcohol was applied, the sheets of corneal epithelium were histiologically examined using light and electron microscopy. Electron microscopy of the samples revealed fragmentsof basement membrane still attached to the epithelial basal cells. The absence of Bowman's layer and stroma indicate where the alcohol separated the epithelium from the stroma. It was also found that by in vitro studies of corneal samples, epithelial cell survival with alcohol is dose and time-dependent. Most cells remained viable with less than 25% alcohol, and an increase in cellular apoptosis occurred with greater than 35 seconds of exposure.