title: [An analysis of changes in posterior corneal elevation and relevant factors after small incision lenticule extraction].
abstract: OBJECTIVE
  To investigate changes in posterior corneal elevation after small incision lenticule extraction (SMILE) and related factors.
  
  
  METHODS
  Retrospective case series study. Eighty-three eyes of 44 myopic patients undergoing SMILE were examined with the Pentacam preoperatively, and at 1 day, 1 month, 3 months, and 6 months postoperatively. Posterior corneal elevation at the corneal apex and 0°, 45°, 90°, 135°, 180°, 225°, 270° and 325° points of the 2 mm and 6 mm diameter (total, 17 points) was analyzed.
  
  
  RESULTS
  The changes in posterior corneal elevation at 1 day, 1 month, 3 months, and 6 months were(-1.72±2.59), (-0.98±2.37), (-0.45±1.81) and (-0.25±2.20) μm, respectively, at the corneal apex. The results were statistically significant (t=6.07, 3.75, 6.07; P<0.05), except 6 months. The changes in posterior corneal elevation were (-1.42±2.06),(-0.69±1.86), (-0.30±1.50) and(-0.22±1.58) μm, respectively, in the 2 mm circle. The results of 1 day and 1 month were statistically significant (t=6.28, 6.28, P<0.05). The changes in posterior corneal elevation were (1.48±1.47),(0.98±1.32),(0.90±1.31) and (0.90±1.16) μm, respectively, in the 6 mm circle .The results were totally statistically significant (t=6.28, 6.28, P<0.05). There were statistically significant differences between 1 month and 1 day postoperatively in the corneal apex, 2 mm and 6 mm circles. The changes were (0.75±2.55),(0.73±1.97) and(-0.50±1.60) μm. There were statistically significant differences between 3 months and 1 month postoperatively in the corneal apex and 2 mm circle. The changes were (0.53±2.22) and (0.39±1.80) μm. No significant change was found in the 6 mm circle. Between postoperative 6 months and 3 months, there were no statistically significant differences. The spherical equivalent, intraocular pressure, ablation depth, residual bed thickness, corneal hysteresis, and corneal resistance factor had no obvious correlation with the changes in posterior corneal elevation.
  
  
  CONCLUSIONS
  After SMILE, the surrounding cornea was slightly forward, while the central posterior cornea was slightly backwards, and returned gradually. The spherical equivalent, intraocular pressure, ablation depth, residual bed thickness, corneal hysteresis, and corneal resistance factor had no obvious correlation with the changes in posterior corneal elevation. (Chin J Ophthalmol, 2016, 52: 494-498).
authors.affiliation: Tianjin Eye Hospital, Clinical College of Ophthalmology, Tianjin Medical University, Tianjin Eye Institute, Tianjin Key Lab. of Ophthalmology and Visual Science, Tianjin 300020, China.
authors.forename: C J
authors.initials: CJ
authors.lastname: Yu
authors.forename: Y
authors.initials: Y
authors.lastname: Wang
authors.forename: X L
authors.initials: XL
authors.lastname: Su
authors.forename: W J
authors.initials: WJ
authors.lastname: Wu
authors.forename: Z Q
authors.initials: ZQ
authors.lastname: Wu
authors.forename: Y N
authors.initials: YN
authors.lastname: Wu
mesh_terms: D003315:Cornea / Q000601:surgery*; D048988:Corneal Surgery, Laser / Q000379:methods*; D019781:Corneal Topography / Q000379:methods*; D006801:Humans; D007429:Intraocular Pressure; D009216:Myopia / Q000601:surgery*; D011184:Postoperative Period; D012189:Retrospective Studies; D013997:Time Factors; D014065:Tonometry, Ocular; D014792:Visual Acuity