We studied the effect of corneal hydration upon ablation rate in excimer laser photorefractive keratectomy (PRK). This variable may alter the subepithelial smoothness and the resulting clarity of the result. The eyes of freshly slaughtered pigs (N=5) and the eyes of Dutchbelted rabbits (N=4) (in vivo) were de-epithelialized and central ablation zones 3.0 to 4.5 mm in diameter were produced in the subepithelial corneal layers using a 193 nm argon fluoride (ArF) ophthalmic excimer laser. Ablation was performed immediately or after a 15-min incubation period in distilled water as a means of inducing corneal edema. Smoothness was evaluated using specular reflection microscopy and showed the water-treated surface to be increasingly less regular than the nonwater-treated samples. Water treatment may affect the final outcome of the PRK procedure and indicates the need to monitor the preoperative cornea for the development of any edema, especially after the epithelium is removed.