Comprehensive Assessment of Posterior Corneal Asphericity Change Calculated by Tangential Radius of Curvature After FS-LASIK and SMILE

PURPOSE: To evaluate changes in posterior corneal asphe- ricity (AQ) using the tangential radius of curvature after fem- tosecond laser-assisted in situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE) procedures. METHODS: One hundred twenty right eyes of myopic patients who underwent either FS-LASIK or SMILE procedures were analyzed using Sirius 3D corneal topography for assessment. The tangential radius was employed to calculate both preoperative and postoperative posterior corneal Q-values across each semimeridian. After both surgical interventions, the AQ value variations across the 360 degrees semimeridional regions of the posterior corneal surface were compared. RESULTS: A marked postoperative increase in the posterior corneal Q-value was documented. No significant differences were noted between the postoperative Q-values or AQ-values of the two surgical approaches. Among patients with mod- erate myopia, postoperative Q-value exhibited considerably lower increases and AQ-value significantly smaller than their counterparts with high myopia. Moreover, the fluctuation in AQ across semimeridional regions was less evident in pa- tients with moderate myopia than in those with high myopia. Notably, the degree of AQ fluctuation across semimeridional regions was similar between both surgical categories. These data offer insights into variations in the posterior corneal surface after refractive surgeries depending on the degree of myopia, illuminating their clinical relevance. CONCLUSIONS: Both FS-LASIK and SMILE introduce notable changes to posterior corneal asphericity among patients with different myopia intensities. Furthermore, the influence on the asphericity across the entire posterior surface is similarly distributed between FS-LASIK and SMILE techniques.