title: Comparison of forward shift of posterior corneal surface after operation between LASIK and LASEK.
abstract: OBJECTIVE
  To compare the forward shift of the posterior corneal surface as a function of time after surgery between successful laser in situ keratomileusis (LASIK) and laser-assisted subepithelial keratectomy (LASEK).
  
  
  METHODS
  Twenty-two eyes from 14 patients who underwent LASIK and 19 eyes from 10 patients who underwent LASEK were reviewed retrospectively. The uncorrected visual acuity, spherical equivalent and pachymetry were obtained before and 1 or 2 weeks and 2, 6, 12, and 24 months after surgery. The change in the elevation of the posterior corneal surface was assessed using the difference map of an Orbscan II (Bausch and Lomb, Salt Lake City, Utah, USA), which was generated from the preoperative and subsequent postoperative elevation map.
  
  
  RESULTS
  One or 2 weeks after LASIK and LASEK, the posterior corneal surface had shifted forward by 18.00 and 25.90 microm, respectively (p = 0.008). However, the mean posterior corneal surface reduced by 3.05 microm from 1 or 2 weeks to 2 years in the LASIK group (p = 0.359). In contrast, the mean posterior corneal surface had reduced by 12.40 microm in the LASEK group (p = 0.004). This forward shift did not return to the corneal normal elevation observed prior to surgery in the two groups.
  
  
  CONCLUSIONS
  Refractive surgery induced a forward shift of the posterior corneal surface early postoperatively in the LASIK and LASEK groups, and this change after LASEK was significantly larger than that observed after LASIK. The posterior corneal surface gradually shifted backwards depending on the time course in both groups, but they did not return to the preoperative levels.
authors.affiliation: Department of Ophthalmology and Visual Science, College of Medicine, The Catholic University of Korea, Seoul, Korea.
authors.forename: Hyojin
authors.initials: H
authors.lastname: Kim
authors.forename: Hyun Jin
authors.initials: HJ
authors.lastname: Kim
authors.forename: Choun-Ki
authors.initials: CK
authors.lastname: Joo
mesh_terms: D000328:Adult; D003315:Cornea / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery; D019781:Corneal Topography; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D049008:Keratectomy, Subepithelial, Laser-Assisted; D020731:Keratomileusis, Laser In Situ; D008297:Male; D009216:Myopia / Q000601:surgery*; D011184:Postoperative Period; D012189:Retrospective Studies; D016896:Treatment Outcome; D014463:Ultrasonography