Predictability of Central Corneal Stromal Reduction After SMILE and FS-LASIK for High Myopia Correction: A Prospective Randomized Contralateral Eye Study

Abstract

PURPOSE: To compare small incision lenticule extraction (SMILE) and femtosecond laser–assisted in situ keratomileusis (FS-LASIK) in terms of the predictability of central stromal thickness reduction in eyes with high myopia. METHODS: In this prospective, randomized contralateral eye trial, 42 patients received SMILE in one eye and FS-LASIK (using the Amaris 750S excimer laser [SCHWIND eye-tech-solutions]) in the fellow eye for the correction of high myopia (manifest refraction spherical equivalent: < −6.00 diopters). Spectral-domain optical coherence tomography was used to measure the central corneal and epithelial thickness. Pre-operative and postoperative values were compared to determine the amount of central stromal reduction achieved. RESULTS: At the 6-month follow-up visit, the amount of central stromal reduction was overestimated by 20.05 ± 5.92 µm in the SMILE group ( P < .0001) and underestimated by 8.21 ± 8.14 µm in the FS-LASIK group ( P < .0001). The mean actual central stromal reduction achieved with SMILE was significantly less than that achieved with FS-LASIK (10.10 ± 18.01 µm, range: 1.90 to 18.29 µm, P < .001). The discrepancy between the planned and achieved central corneal stromal reduction was not associated with refractive overcorrection or undercorrection in either the SMILE group or the FS-LASIK group ( P = .9743 vs P = .0777). CONCLUSIONS: In patients with high myopia, the laser software platform may underestimate and overestimate the amount of actual corneal reduction in eyes treated with FS-LASIK and SMILE, respectively. SMILE required less corneal stroma compared to FS-LASIK in the studied cohort using the Amaris 750S excimer laser when correcting a similar spherical equivalent refraction. [ J Refract Surg . 2022;38(2):90–97.]