Study of Corneal and Retinal Thicknesses at Five Years after FS-LASIK and SMILE for Myopia

Abstract BACKGUOND: This study aimed to compare corneal and retinal thicknesses at 5 years after femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE) for myopia, investigate the effect of epithelial remodeling on refractive status. METHODS: Patients who received FS-LASIK or SMILE 5 years before were enrolled in this cross-sectional study. After 1:1 propensity score matching, each surgical group obtained 177 patients (177 eyes). Visual acuity and refraction were measured in this visit at 5 years after surgery. Corneal and retinal thickness maps were generated by spectral domain optical coherence tomography (SD-OCT). The Quality of Vision (QoV) questionnaire was used to assess visual symptoms and overall satisfaction. Thicknesses between groups were compared, contributing factors were analyzed, and correlations between epithelial thickness (ET), postoperative refractive status and overall satisfaction were evaluated. RESULTS: Compared to SMILE group, central and paracentral ET of FS-LASIK group were thicker, pericentral ET was thinner, and the discrepancy of ET between central and pericentral zones was larger (all P<0.05). This discrepancy was correlated with postoperative spherical equivalent (SE) and myopic regression (all P<0.05) in both groups, but not correlated with QoV scores and overall satisfaction (both P>0.05). There was no statistical difference in stromal thickness (ST) and total corneal thickness (all P>0.05). Most annuluses of ET and ST were linearly related to preoperative SE (all P<0.05). Statistical difference of ET between high and super-high myopia groups only was found in supratemporal section of pericentral zone in SMILE group (P=0.012). Macular thickness, ganglion cell complex thickness and retinal nerve fiber layer thickness of two groups had no statistical difference (all P>0.05). CONCLUSION: The tendency that ET in central zone was thicker than peripheral zone was more obvious at 5 years after FS-LASIK compared to SMILE. This tendency was also more significant in patients with higher degree of myopia. Epithelial remodeling might be one of the reasons of myopic regression, but it had little effect on patients' subjective visual quality and satisfaction. Retinal thickness was not affected by these two surgical methods.