Seven-Year Observation of Posterior Corneal Elevations After Small Incision Lenticule Extraction in Myopic Patients with Thin Corneas.

Purpose: To assess the long-term stability of the posterior corneal surface in myopic patients with thin corneas after Small Incision Lenticule Extraction (SMILE).

Methods: This study involved 60 eyes from 60 patients (mean spherical equivalent (SE): -5.81 ± 1.79 D), divided into two groups based on preoperative central corneal thickness (CCT): Group A (CCT < 510 μm, thin cornea) and Group B (CCT ≥ 510 μm, normal cornea), with 30 eyes per group. Data collected preoperatively and 7 years postoperatively included visual acuity, SE, efficacy and safety indices, intraocular pressure, axial length, and posterior corneal surface elevation measured by Pentacam.

Results: No significant long-term complications were observed. Efficacy and safety indices were similar: 0.94 ± 0.16 and 1.07 ± 0.11 in Group A, and 0.94 ± 0.17 and 1.07 ± 0.16 in Group B. In Group A, posterior central elevation (PCE) increased significantly from baseline, while posterior thinnest elevation (PTE) decreased. Group B showed a significant increase in mid-peripheral elevation at 4 mm (MPE-4 mm). Subgroup analysis revealed increased PTE and MPE-6 mm in low-to-moderate myopia in Group A, and increased peripheral elevations in similar myopia levels in Group B. High myopia patients showed no significant changes. Correlation analysis in Group A showed that changes in 7-year PTE were negatively correlated with residual bed thickness (RBT) and positively correlated with the ablation ratio (AR). Similarly, changes in PCE and PTE correlated with RBT and AR.

Conclusion: SMILE effectively corrects myopia long-term but increases posterior surface elevation in thin corneas. Patients with high myopia and thin corneas should monitor RBT and AR to ensure long-term corneal stability and safety.