Human corneal ablation threshold using the 193-nm ArF excimer laser.

PURPOSE To determine the human corneal threshold ablation energy density for the 193-nm ArF excimer laser, approximating clinical conditions. METHODS The VISX Star (Santa Clara, CA) 193-nm argon fluoride excimer laser was used to ablate the cornea in human eye bank eyes under clinical conditions. Corneas were exposed to energy densities of 10, 20, 30, 35, 40, 45, and 140 to 160 mJ/cm2. Corneas were fixed for light and transmission electron microscopy immediately after laser exposure. RESULTS Different ablation thresholds for various corneal structural elements were observed. The ablation threshold for the collagen in the corneal stroma was determined to be 30 mJ/cm2. Keratocytes had ablation thresholds of 40 mJ/cm2. These different ablation thresholds accounted for the production of stromal peaks and valleys, with the keratocytes atop the peaks. CONCLUSIONS Different corneal structural elements have different ablation threshold energy densities.