Diameters of Topographic Optical Zone and Programmed Ablation Zone for Laser in situ Keratomileusis for Myopia

To compare topographic optical zones with programmed ablation zone settings of eyes treated with laser in situ keratomileusis (LASIK) for myopia using the VISX S2 excimer laser.Two-hundred three eyes treated with LASIK using the VISX S2 excimer laser were retrospectively evaluated to determine the size of the topographic optical zone. Three to six months after LASIK, the topographic optical zone was measured at the zone of highest curvature on topography and subtraction topography. Eyes were divided into four groups (A, B, C, D) in order of increasing myopia.When the topographic optical zone was compared with the programmed ablation zone, an optical zone reduction of 0.5 +/- 0.1 mm and 0.4 +/- 0.1 mm was found for the longest and shortest diameters, respectively. For eyes with spherical ablation zones, this reduction was 0.6 +/- 0.1 mm and 0.4 +/- 0.1 mm shorter than the programmed horizontal and vertical dimensions. Groups A, B, C, and D, in order of increasing myopia, all showed reductions of approximately 0.5 +/- 0.1 mm for the longest and 0.3 to 0.4 +/- 0.1 mm for the shortest diameters of the optical zone.The topographic optical zone was reduced from the programmed ablation zone. This reduction was statistically significant for both elliptical and spherical ablations, and seemed to be independent of the amount of myopia.