Regional analysis of posterior corneal elevation after laser refractive surgeries for correction of myopia of different degrees

Purpose: To evaluate regional changes in the posterior corneal elevation after three laser refractive surgeries for correction of myopia of different degrees. Settings and Design: Retrospective, comparative, and non-randomized study. Methods: Two hundred patients (200 eyes) who underwent laser epithelial keratoplasty (LASEK), femtosecond-assisted laser in-situ keratomileusis (FS-LASIK), and small-incision lenticule extraction (SMILE) were included in this study. According to preoperative spherical equivalent (SE), each surgical group was divided into two refractive subgroups: low-to-moderate myopia (LM group) and high myopia (H group). The posterior corneal elevation from Pentacam Scheimpflug tomography was analyzed preoperatively and at 1 month, 3 months, 6 months, and 12 months postoperatively. Three subregions of the posterior cornea were divided in this study as the central, paracentral, and peripheral regions. Statistical Analysis Used:Generalized Estimating Equations (GEE). Results: For all three surgical groups, similar changing trends were seen in the two refractive subgroups. H group presented a larger changing magnitude than the LM group in FS-LASIK over time (P < 0.05), whereas no significant difference was noted in the two refractive subgroups of LASEK or SMILE (P > 0.05). At 12 months postoperatively, the central posterior corneal elevation returned to the preoperative level in LASEK (P > 0.05) but shifted forward significantly in FS-LASIK and SMILE (P < 0.05). Conclusion: Different posterior corneal regions respond differently to corneal refractive surgeries. LASEK, FS-LASIK, and SMILE demonstrate different trends in the regional changes in posterior corneal elevation. The corneal shape seems more stable in LASEK than in FS-LASIK and SMILE.