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.