title: Posterior corneal surface changes after hyperopic laser in situ keratomileusis.
abstract: OBJECTIVE
  To evaluate posterior corneal surface topographic changes after hyperopic laser in situ keratomileusis (H-LASIK) using Orbscan I (Orbtek, Inc.).
  
  
  METHODS
  Department of Ophthalmology, Nara Medical University, Nara, Japan.
  
  
  METHODS
  In 25 eyes of 15 patients who had H-LASIK, the posterior corneal surface was measured with slit-scanning corneal topography (Orbscan I) preoperatively and 1 year postoperatively. The center as a fit zone and calculated posterior corneal surface changes were taken at 4 points: nasal, temporal, superior, and inferior sides in the 5.0 mm diameter. The posterior corneal topographic changes were analyzed using an analysis of variance. The postoperative:preoperative magnification ratio of the posterior corneal surface was calculated in a theoretical eye model.
  
  
  RESULTS
  When a "+" reading was defined as the forward displacement and "-" was defined as the backward displacement, the mean posterior corneal topographic changes were -2.8 microm +/- 27.9 (SD) at the nasal side, -4.5 +/- 27.8 microm at the temporal side, -3.9 +/- 20.1 microm at the superior side, and -2.3 +/- 20.1 microm at the inferior side. The posterior corneal surface between any 2 examined points showed no significant difference after H-LASIK. In addition, the hypothetical change in the posterior cornea was -8.3 microm after +3.0 diopter H-LASIK, which was approximately closer to the study results. In each side, the amount of the attempted correction was significantly correlated with the posterior corneal topographic change.
  
  
  CONCLUSIONS
  Clinical measurement of the posterior corneal displacement after H-LASIK with Orbscan revealed a backward shift. This change corresponded to the hypothetical artifactual changes with Orbscan; that is, changes in the magnification ratio.
authors.affiliation: Department of Ophthalmology, Nara Medical University, Nara, Japan. tueda@naramed-u.ac.jp
authors.forename: Tesuo
authors.initials: T
authors.lastname: Ueda
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Nawa
authors.forename: Kozo
authors.initials: K
authors.lastname: Masuda
authors.forename: Hidetoshi
authors.initials: H
authors.lastname: Ishibashi
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Hara
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Uozato
mesh_terms: D000328:Adult; D000368:Aged; D015350:Contrast Sensitivity; D003315:Cornea / Q000503:physiopathology; D019781:Corneal Topography; D004728:Endothelium, Corneal / Q000503:physiopathology*; D006801:Humans; D006956:Hyperopia / Q000503:physiopathology / Q000601:surgery*; D020731:Keratomileusis, Laser In Situ; D008875:Middle Aged; D008962:Models, Theoretical