DIFFRACTIVE SMOOTHING OF EXCIMER-LASER ABLATION USING A DEFOCUSED BEAM

OBJECTIVE: To determine if excimer laser myopic ablation with a defocu sed laser image produces a smoother ablation profile than does focused laser light. METHODS: An ArF excimer laser was used to ablate a 5.00- diopter myopic correction in test blocks using both a contracting and expanding iris aperture. Defocused ablation was performed using a cont racting iris aperture by translating the target away from the laser so urce. A confocal laser scanning microscope was used to analyze the sur face smoothness at 55 x and 275 x magnifications. RESULTS: The confoca l laser scanning micrographs revealed a series of sharply demarcated c oncentric ridges in the focused ablation, and less prominent, slightly wavy lines in the defocused ablation performed with a contracting ape rture. The focused ablation with an expanding aperture also created co ncentric ridges toward the periphery, but with slightly smoother edges . CONCLUSION: Micrographic analysis of the surface profile of excimer laser myopic ablation using a variable iris aperture revealed the pres ence of concentric ridges following focused ablation and smooth curvil inear lines when ablation was performed with a defocused image.