Comparison of Corneal Power and Astigmatism between Simulated Keratometry, True Net Power, and Total Corneal Refractive Power before and after SMILE Surgery

Purpose. To compare the mean corneal power (Km) and total astigmatism (Ka) estimated by three methods: simulated keratometry (simK), true net power (TNP), and total corneal refractive power (TCRP) before and after femtosecond laser small incision lenticule extraction (SMILE) surgery. Methods. A retrospective, cross-sectional study. SimK, TNP, and TCRP from a Scheimpflug analyzer were obtained from 144 patients before and 6 months after SMILE surgery. Km and Ka were recorded as the mean of individual paracentral rings of 1.0 to 8.0 mm (R1 to R8). The surgically induced changes in Km (delta-simK, delta-TNP, and delta-TCRP) and Ka (delta-simKa, delta-TNPa, and delta-TCRPa) were compared to the changes in spherical equivalent of the cycloplegic refraction (delta-SE) and astigmatism (delta-RA). Results. Preoperatively, astigmatism values were greatest with simKa from R1 to R5 and greatest with TCRPa from R6 to R8. Astigmatism values were smallest with TNPa from R1 to R7. Postoperatively, astigmatism values were greatest with simKa from R1 to R5 and greatest with TCRPa from R6 to R8. Delta-TCRP(3) and Delta-TCRP(4) matched delta-SE most closely, and delta-TCRPa(3) matched delta-RA most closely. Conclusions. TCRP proved to be the most accurate method in estimating corneal power and astigmatism both before and after SMILE surgery.