Three-Year Stability of Posterior Corneal Elevation After Small Incision Lenticule Extraction (SMILE) for Moderate and High Myopia

PURPOSE: To investigate long-term changes in posterior corneal elevation after small incision lenticule extraction (SMILE). METHODS: Thirty-six eyes of 20 patients (7 male, 13 female) who underwent SMILE were recruited for this prospective consecutive study. The mean preoperative manifest spherical equivalent was -6.24 +/- 1.47 diopters (D) (range: -3.88 to -8.75 D). Posterior corneal surfaces were measured by a Scheimpflug camera (Pentacam; Oculus Optikgerate GmbH, Wetzlar, Germany) preoperatively and at 1 month, 6 months, 12 months, 2 years, and 3 years after surgery. Posterior central elevation (PCE), posterior maximal elevation (PME), and posterior elevation at the thinnest corneal point (PTE) in the central 4 mm area above the best fit sphere (BFS) were analyzed. The BFS was the same across all followup periods and determined by the preoperative data. A P value of less than.05 was considered statistically significant. RESULTS: All surgeries were executed without complications and no case of keratectasia was observed during the follow-up. An uncorrected distance visual acuity of 20/20 or better was achieved in 100% of eyes at the last visit. The mean change of PCE, PME, and PTE at 3 years after the operation was -2.39 +/- 2.85, 0.50 +/- 3.33, and -2.33 +/- 2.90 mu m, respectively. There were significant differences in the measurements of PCE and PTE before surgery and 3 years after surgery (P =.009); however, there was no significant difference in PME before surgery and 3 years after surgery (P = 1.000). No correlation was found between changes in posterior corneal elevation and residual bed thickness, ablation depth, and preoperative thinnest corneal thickness. CONCLUSIONS: The posterior corneal surface, measured using the Pentacam, was stable after SMILE in the long-term follow-up. The cause of the slight backward change of PCE and PTE needs further study.