Excimer laser keratectomy for myopia with a rotating-slit delivery system.

We performed argon fluoride excimer laser (193-nm) superficial keratectomy for myopia on human donor eyes and on a resected corneal disc. The laser beam was shaped by a rotating slit to produce a circular ablation 7.5 mm in diameter, with a mathematically defined profile to correct myopia. The fluence at the surface of the cornea was 200 mJ/cm2; the laser was fired at 20 Hz. Each 4.5-mJ laser pulse etched a 0.17-micron deep image of the slit in the cornea. Since the slit moved (0.03 Hz), each successive pulse etched an area adjacent to the previous one, reducing damage from repetitive pulses striking the same area. The slit scanned the cornea many times and the summation of these individual ablations produced the smooth myopic ablation profile, as shown by computerized keratographs and light and electron microscopy.