title: Model for nonectatic increase in posterior corneal elevation after ablative procedures.
abstract: OBJECTIVE
  To evaluate the response of the posterior cornea after uneventful laser in situ keratomileusis (LASIK) with scanning-slit videokeratography using the change in elevation as a measure of biomechanical remodeling.
  
  
  METHODS
  Hong Kong Sanatorium and Hospital, Hong Kong, China.
  
  
  METHODS
  Three schematic models of possible posterior corneal response mechanisms to laser refractive surgery were proposed: model A, isolated central bulging; model B, forward shift over a large region of the posterior surface; model C, backward peripheral movement into the anterior chamber. A retrospective study was performed to determine which model was consistent with posterior corneal behavior in 2380 eyes of 1255 patients after myopic LASIK performed with the Technolas 217 laser (Bausch & Lomb). Patients received preoperative and 6-month postoperative Orbscan I (version 2.0, Bausch & Lomb) examinations. Preoperative posterior elevation maps were subtracted from postoperative maps of 2380 eyes using 3 fitting protocols. Difference maps were averaged and the results compared to the proposed schematic models. All topography data processing was done using the Ohio State University Corneal Topography Tool.
  
  
  RESULTS
  Significant central increases in posterior elevation corresponded with significant peripheral decreases in posterior elevation. This pattern is consistent with schematic model C, backward peripheral movement of the posterior cornea, possibly due to a differential pattern of swelling.
  
  
  CONCLUSIONS
  Increases in central posterior corneal elevation after LASIK appear to be dominated by backward peripheral corneal swelling into the anterior chamber rather than forward "bulging" of the central posterior cornea. This is consistent with stable remodeling of the corneal shape due to a surgically induced change in structure and fluid balance, rather than an ectatic event.
authors.affiliation: Department of Ophthalmology and the Biomedical Engineering Center, The Ohio State University, Columbus, Ohio 43210, USA.
authors.forename: Deborah M
authors.initials: DM
authors.lastname: Grzybowski
authors.forename: Cynthia J
authors.initials: CJ
authors.lastname: Roberts
authors.forename: Ashraf M
authors.initials: AM
authors.lastname: Mahmoud
authors.forename: John S
authors.initials: JS
authors.lastname: Chang
mesh_terms: D001251:Astigmatism / Q000473:pathology / Q000601:surgery; D001696:Biomechanical Phenomena; D003315:Cornea / Q000473:pathology*; D003319:Corneal Stroma / Q000473:pathology; D019781:Corneal Topography; D004108:Dilatation, Pathologic; D006801:Humans; D020731:Keratomileusis, Laser In Situ; D008954:Models, Biological; D009216:Myopia / Q000473:pathology / Q000601:surgery*; D011183:Postoperative Complications; D012189:Retrospective Studies