Laser-induced Fluorescence During Photorefractive Keratectomy: A Method for Controlling Epithelial Removal

Purpose Laser-induced fluorescence is generated during ablation of corneal tissue with the argon-fluoride 193-nm excimer laser. To investigate possible changes in laser-induced fluorescence spectra emitted during the transition between epithelium and stroma, we developed a system using an intensified charge-coupled device to achieve fast per-pulse temporal resolution of laser-induced fluorescence. Methods Freshly enucleated human cadaver eyes were subjected to 193-nm excimer laser keratectomy. During the procedure, laser-induced fluorescence was measured using an intensified charge-coupled device. Changes in laser-induced fluorescence were detected and used to control epithelial removal. Depth of ablation was determined histologically. Results The 193-nm excimer laser pulses induced both visible and ultraviolet fluorescence from corneal epithelium and stroma. In each layer two peaks predominated, one at 405 nm and the other at 346 nm. There was a rapid threefold reduction in the 346-nm ultraviolet peak at the transition from epithelium to stroma. Conclusions By monitoring changes in laser-induced fluorescence at the epithelial-stromal interface, the clinician may be able to control corneal epithelial removal more precisely and reproducibly before performing photorefractive ablation.