Abstract
AIM: To investigate the changes in posterior corneal elevation within 6mo after small incision lenticule extraction (SMILE) surgery for myopia and myopic astigmatism in patients with thin corneas. METHODS: A prospective study included patients with thin corneas (preoperative thinnest corneal thickness ranging from 480 to 520 µm) who underwent SMILE for myopia or myopic astigmatism. Corneal topography and posterior corneal elevation were assessed using Pentacam HR at three time points: preoperatively, 1mo, and 6mo postoperatively. The measured parameters included thinnest point elevation (PTE), posterior maximal elevation (PME), posterior central elevation (PCE), and 24 additional reference points. RESULTS: A total of 106 eyes from 106 patients (age range: 18-34) were included in the study. Uncorrected distance visual acuity (UDVA) improved significantly, with a mean logMAR value of -0.07±0.06 at the final follow-up visit. Measurements of posterior corneal elevation showed no significant changes in most points, hemispheres, and meridians at 6mo postoperatively. Notably, only two points, ∆E(2mm-45°) and ∆E(2mm-90°), exhibited statistically significant elevation changes: the elevation of ∆E(2mm-45°) increased from -2.3±4.99 to -1.0±5.9 µm (P=0.0037), and that of ∆E(2mm-90°) increased from -16±7.53 to -15±7.4 µm (P=0.016). However, these changes were within the measurement error range of the Pentacam HR (±5 µm in a 5 mm area). CONCLUSION: SMILE surgery is a safe and stable procedure for correcting myopia or myopic astigmatism in patients with thin corneas, as evidenced by the stability of posterior corneal elevation.