The impact of corneal epithelial remodeling on visual quality after SMILE and FS-LASIK for high myopia.

Background: To investigate the corneal epithelial remodeling profile after small incision lenticule extraction (SMILE) and femtosecond laser in situ keratomileusis (FS-LASIK) for high myopia, as well as its possible consequence for subjective and objective changes in visual quality.

Methods: This prospective observational study included 72 eyes with high myopia, divided into two groups, who underwent either SMILE or FS-LASIK. In addition to standard evaluation, anterior segment optical coherence tomography was used to assess central 6-mm corneal epithelial thickness (ET) before surgery and at 1 week, 1, 3, and 6 months after surgery; ET inhomogeneity across the central 5- and 6-mm cornea was quantified using the coefficient of variance (CV). The objective optical quality includes the modulation transfer function cut off frequency (MTF cut off), Strehl ratio, objective scatter index (OSI), and mean OSI obtained using the Optical Quality Analysis System-II. Patient-reported quality of vision was determined with a modified National Eye Institute Refractive Error Quality of Life questionnaire. The correlation of postoperative ET and treatment parameters with visual quality related parameters was analyzed.

Results: Both ET and CV were significantly increased in the SMILE and FS-LASIK groups at 6 months postoperatively (P < 0.001). Paracentral ET was positively correlated with changes in MTF cut off and Strehl ratio at 1 week after SMILE (0.338, 0.405, separately, P < 0.05). For FS-LASIK, ET was negatively correlated with MTF cut off change at 1, 3, 6 months postoperatively (-0.334, -0.385, -0.375, separately, P < 0.05); Central 6-mm CV and Strehl ratio significant correlated at 6 months (-0.427, P = 0.01); ET was significantly correlated with patient-reported quality of vision (P < 0.05). No correlation was found between preoperative spherical equivalent, keratometry values, total corneal thickness, optical zone, and ablation depth and changes in visual quality parameters.

Conclusions: Correction of high myopia with SMILE and FS-LASIK induced epithelial remodeling involved an increase in ET and ET inhomogeneity. Epithelial changes in different regions have different effects on subjective and objective visual quality, which may have a certain clinical relevance of the corneal epithelial thickness measurement for visual quality assessment after refractive surgery.