Customized and low spherical aberration corneal ablation design

PURPOSE: The purpose of this study was to use the Arizona Eye Model to help guide customization of corneal excimer ablation and reduce spherical aberration. METHODS: Myopic eyes were treated with the Nidek EC-5000 excimer laser with a 5.5-mm diameter optic ablation zone and a 7.0-mm diameter transition ablation zone. We analyzed preoperative and postoperative corneal topographies using height mapping. From this data, refractive error profiles and maps were constructed using the Arizona Eye Model. The first group of patients had refractions between -2.00 and -5.00 D. Data was obtained by subtracting postoperative topography from preoperative topography. We then plotted the ideal ablation pattern if no additional spherical aberration was introduced when compared to preoperative topographies. RESULTS: We found that in the central 4 mm, the ablation pattern was highly acceptable, with negligible spherical aberration. As the ablation moved out toward 6 mm, there was increasing spherical aberration. Newer ablation designs require more flattening in the midperiphery of the cornea. These flatter peripheral designs require more blending in the periphery and larger transition zones. CONCLUSION: The use of computerized corneal topography in eye modeling is helpful in designing new ablation patterns to reduce optical and spherical aberration. Ablation zone design is critical to maximizing optical and biologic tolerance.