title: Three-Year Stability of Posterior Corneal Elevation After Small Incision Lenticule Extraction (SMILE) for Moderate and High Myopia.
abstract: OBJECTIVE
  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 Optikgeräte 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 follow-up 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 µm, 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. [J Refract Surg. 2017;33(2):84-88.].
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhao
authors.forename: Weijun
authors.initials: W
authors.lastname: Jian
authors.forename: Yingjun
authors.initials: Y
authors.lastname: Chen
authors.forename: Michael C
authors.initials: MC
authors.lastname: Knorz
authors.forename: Xingtao
authors.initials: X
authors.lastname: Zhou
mesh_terms: D000293:Adolescent; D000328:Adult; D003319:Corneal Stroma / Q000601:surgery*; D048988:Corneal Surgery, Laser / Q000379:methods*; D019781:Corneal Topography; D004108:Dilatation, Pathologic / Q000175:diagnosis; D004728:Endothelium, Corneal / Q000473:pathology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D047728:Myopia, Degenerative / Q000503:physiopathology / Q000601:surgery*; D010781:Photography; D011446:Prospective Studies; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult