Aspheric Photorefractive Keratectomy With Excimer Laser

Abstract

Increased spherical aberration of the cornea is a common finding after excimer laser keratorefractive keratectomy. The shape of the paracentral cornea is probably related to the incidence of side effects like glare and halos at night depending on ablation zone size and pupil diameter. Aspheric curvature changes of the paracentral cornea at the edge of the ablation may decrease those side effects. Fifteen patients were treated with photorefractive keratectomy for myopia correction with a Summit excimer laser (Summit Technology, Waltham, Mass), one eye using a standard spherical algorithm and the fellow eye using a new aspherical algorithm. Eyes were followed for 6 to 18 months. None of 15 patients reported halos in the aspherically corrected eye stronger than in the fellow eye, whereas five patients claimed stronger halos in the spherically corrected eye. The effective clear zone size was 3.16 +/- 0.35 mm in the spherical cases compared to 3.43 +/- 0.31 in the aspherical cases, although the same ablation zone diameters of 5 mm were used. This difference is highly statistically significant. Effective spherical aberration based on raytracing analysis of the central 5 mm of the corneal topographic maps was significantly smaller in the corneas with aspheric correction than in those with spheric corrections. These results indicate better optical homogeneity in eyes after aspheric photorefractive keratectomy for myopia compared to standard spherical corrections.