title: Efficacy of Orbscan II and Pentacam topographers by a repeatability analysis when assessing elevation maps in candidates to refractive surgery.
abstract: BACKGROUND
  Anterior and posterior corneal elevations are measurements used to detect keratoconus suspects.
  
  
  OBJECTIVE
  To determine the efficacy of Orbscan II and Pentacam when assessing their elevation maps.
  
  
  METHODS
  The efficacy of the Orbscan II and Pentacam measuring the anterior and posterior corneal elevations were evaluated in a sample of 68 eyes. The concordance between the two devices and the coefficient of repeatability were measured following the parameters of the British Standard Institution by the Bland-Altman concordance analysis and the Lin concordance correlation coefficient.
  
  
  RESULTS
  The coefficient of repeatability at the point of maximum anterior elevation was 68.29% with the Orbscan and 24.20% with the Pentacam. The concordance correlation coefficient was 0.64 (CI 95%: 0.48-0.76) with the Orbscan and 0.94 with the Pentacam (CI 95%: 0.91-0.96). The coefficient of repeatability at the point of maximum posterior elevation was 38.7% with the Orbscan and 68.0% with the Pentacam. The concordance correlation coefficient was 0.69 with the Orbscan (CI 95%: 0.55-0.80) with a precision of 0.71 and an accuracy of 0.97, and 0.24 with the Pentacam (CI 95%: 0.00-0.45) with a precision of 0.24 and an accuracy of 0.99.
  
  
  CONCLUSIONS
  Measurement of the point of maximum posterior elevation is better with the Orbscan II and less precise with the Pentacam. The random error can be reduced by using the mean of three assessments and can serve as a guide in the search of diagnostic devices with minimum absolute relative error in all measurements.
authors.affiliation: Clínica de Oftalmología de Cali, Colombia. ximena@visionsana.com <ximena@visionsana.com>
authors.forename: María Ximena
authors.initials: MX
authors.lastname: Núñez
authors.forename: Claudia
authors.initials: C
authors.lastname: Blanco
mesh_terms: D000328:Adult; D019781:Corneal Topography / Q000295:instrumentation*; D006801:Humans; D007640:Keratoconus / Q000473:pathology*; D008875:Middle Aged; D054140:Refractive Surgical Procedures; D015203:Reproducibility of Results; D055815:Young Adult