The confines of our knowledge with respect to excimer laser photorefractive keratectomy are particularly manifest in two areas: the effects of the excimer on the corneal tissue, especially in the course of the wound healing process; and the optical aberrations caused by the laser treatment through structural alterations in a previously clear cornea. The criteria currently used to evaluate the outcome of excimer refractive surgery are not adequate. More stringent and nuanced assessments are needed to expand the frontiers of our knowledge.