Theoretical analysis of ablation depths and profiles in laser in situ keratomileusis for compound hyperopic and mixed astigmatism

Purpose: To compare the theoretical ablation depths and profiles of 4 treat ment strategies for compound hyperopic and mixed astigmatism. Setting: Theoretical analysis. Methods: Corneal contour drawings of theoretical corneal ablation profiles during laser in situ keratomileusis (LASIK) and photoastigmatic refractive keratectomy were made. The depths of tissue ablation in 4 treatment strateg ies for compound hyperopic astigmatism (Groups 1 to 4) and for mixed astigm atism (Groups 5 to 8) were compared: (1) combined hyperopic spherical and m yopic cylindrical treatments (Groups 1 and 5); (2) combined spherical and h yperopic cylindrical treatments (Groups 2 and 6); (3) combined cylindrical treatments (Groups 3 and 7); (4) combined cross-cylinder and spherical equi valent treatments (Groups 4 and 8). Results: In compound hyperopic astigmatism, the 4 approaches resulted in id entical final curvatures, but the ablation depths were greatest in Group 1 (combined hyperopic spherical and myopic cylindrical treatments). The small est amount of ablation occurred in Group 2 (combined hyperopic spherical an d hyperopic cylindrical treatments) and Group 3 (combined hyperopic cylindr ical treatments), which had similar tissue ablation patterns. In mixed asti gmatism, the greatest ablation depth was in Group 5, followed by Group 8, a nd Groups 6 and 7. The tissue ablation depths and profiles were similar in Groups 6 and 7. Conclusion: The treatment approaches in Groups 2, 3, 6, and 7 (which avoide d the use of minus cylinder) resulted in the smallest degree of stromal abl ation. Patients with compound hyperopic or mixed astigmatism may benefit fr om reduced ablation depths by deferring treatment until hyperopic cylindric al and/or combined cylindrical treatments are available. J Cataract Refract Surg 2000; 26:1123-1136 (C) 2000 ASCRS and ESCRS.