title: Topography-based screening for previous laser in situ keratomileusis to correct myopia.
abstract: OBJECTIVE
  To demonstrate the feasibility of developing a screening tool based on corneal topography to detect previous myopic laser in situ keratomileusis (LASIK).
  
  
  METHODS
  Clinical data from a private clinic analyzed in a university setting.
  
  
  METHODS
  Two hundred thirty-three topographies were randomly selected so 1 topography per patient was used: 150 from unoperated corneas and 83 from corneas that had LASIK to correct myopia. The mean surgical correction was -4.40 diopters (D) +/- 2.53 (SD) (range -11.00 to -0.38 D). All topographies were performed using an Orbscan II unit (Bausch & Lomb Surgical). The LASIK procedures were performed using a Technolas 217C excimer laser and a Hansatome microkeratome (Bausch & Lomb Surgical). The algorithms used the mean value of the directional derivative (DT) of the anterior tangential curvature of the cornea in the 2.2 mm radius central disk and the mean value of the anterior elevation (E) with respect to the best-fit sphere in the 0.5 mm radius central disk. Topographies in the testing set (n = 119) were classified as operated if E < 0 (E algorithm) or DT > 0 (DT algorithm) or as unoperated.
  
  
  RESULTS
  The E algorithm yielded 0% false positives and 16.7% false negatives and the DT algorithm, 6.5% and 7.1%, respectively. For myopia greater than -1.12 D, the DT algorithm provided a 0% false negative rate. The performance of E and DT algorithms, used in combination, was superior to clinical assessment.
  
  
  CONCLUSIONS
  Criteria based on Orbscan II corneal topography are proposed for the detection of previous myopic LASIK performed with a Technolas 217C excimer laser.
authors.affiliation: Department of Computer Science and Operations Research, University of Montreal, Montreal, Quebec, Canada.
authors.forename: François
authors.initials: F
authors.lastname: Destrempes
authors.forename: Isabelle
authors.initials: I
authors.lastname: Brunette
authors.forename: Jean
authors.initials: J
authors.lastname: Meunier
authors.forename: Mylène
authors.initials: M
authors.lastname: Beyrouthy
authors.forename: Pierre
authors.initials: P
authors.lastname: Demers
authors.forename: Sameh
authors.initials: S
authors.lastname: Fanous
authors.forename: Guy
authors.initials: G
authors.lastname: Doyon
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000465:Algorithms; D019781:Corneal Topography; D005188:False Negative Reactions; D005189:False Positive Reactions; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D020731:Keratomileusis, Laser In Situ; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009216:Myopia / Q000601:surgery*; D015351:Vision Screening / Q000379:methods*