Comparison of Optical Zone Decentration after SMILE and FS-LASIK for Low and Moderate Myopia

Objective: To compare the optical zone decentration between small incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) in treating myopia and astigmatism, and to analyze the correlation between the decentration distance and corneal higher-order aberrations (HOAs), angle kappa, spherical equivalent (SE), and the dominant eye. Methods: This research was based on the retrospective analysis of 62 patients (124 eyes) who had undergone SMILE and 44 patients (88 eyes) who had undergone FS-LASIK in Guangzhou Aier Eye Hospital between January 2018 and October 2018. Based on the 3-month postoperative tangent curvature [front] map of Pentacam, the 6 mm cutting boundary was fitted with a self-made concentric circle and the distance from the center to the top of the cornea was recorded as decentration. Independent t-tests, Pearson correlation coefficient analysis, and a chi-square test were used to analyze the collected data. Results: The decentration was 0.27±0.14 mm for SMILE and 0.25±0.13 mm for FS-LASIK, and there was no statistically significant difference between the groups. There was a correlation between decentration distance and coma (r=0.288, P=0.009) for FS-LASIK but not for SMILE. There was no correlation between decentration distance and angle kappa or SE for both groups. There was no significant difference in eccentricity between the dominant and non-dominant eye in both groups. Conclusions: The accuracy of the manual centration location of SMILE is similar to that of the automatic centration location of FS-LASIK. There is a correlation between decentration distance and coma for FS-LASIK, but not for SMILE. There is no correlation between decentration distance and angle kappa, SE, or the dominant eye. Key words: small incision lenticule extraction; laser in situ keratomileusis; center shift; angel kappa; aberration