title: Repeatability of Keratometry Measurements Obtained With Three Topographers in Keratoconic and Normal Corneas.
abstract: OBJECTIVE
  To assess the repeatability of the corneal topography functions of Orbscan II (Bausch & Lomb, Rochester, NY), OPD-Scan III (Nidek, Gamagori, Japan), and iTrace (Tracey Technologies, Houston, TX) in keratoconic eyes and in a control group of normal patients.
  
  
  METHODS
  In this prospective cohort study, patients were recruited between November 2011 and May 2012. Measurements were performed with a combined Placido-scanning slit system (Orbscan II) and two combined Placido-aberrometer systems (OPD-Scan III and iTrace). Repeatability limit and intraclass correlation coefficients (ICCs) of keratometric readings were calculated.
  
  
  RESULTS
  Fifty-nine keratoconic eyes of 34 patients and 54 normal eyes of 27 patients were included. Three groups were evaluated: all stage I-IV keratoconic eyes (59 eyes), a subgroup consisting of stage I-II keratoconic eyes (41 eyes), and normal eyes (54 eyes). For almost all parameters studied, the repeatability limit was higher in the two groups of keratoconic eyes compared to normal eyes with all three topographers, indicating lower repeatability. For the maximum keratometry measurement, repeatability limit was 1.73, 1.49, and 1.41 diopters (D) in the stage I-IV keratoconic eyes group, 1.11, 1.02, and 0.98 D in the stage I-II keratoconic eyes group, and 0.61, 0.37, and 1.02 D in the normal eyes group with Orbscan II, OPD-Scan III, and iTrace, respectively.
  
  
  CONCLUSIONS
  Topographies performed in keratoconic eyes are less repeatable than those performed in normal eyes. Threshold values of keratometric changes used to ascertain keratoconus progression should be carefully considered. Caution should be taken when interpreting the topographies of such patients. The higher variability should be taken into account before performing any treatment.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Guilbert
authors.forename: Alain
authors.initials: A
authors.lastname: Saad
authors.forename: Maud
authors.initials: M
authors.lastname: Elluard
authors.forename: Alice
authors.initials: A
authors.lastname: Grise-Dulac
authors.forename: Hélène
authors.initials: H
authors.lastname: Rouger
authors.forename: Damien
authors.initials: D
authors.lastname: Gatinel
mesh_terms: D000328:Adult; D015331:Cohort Studies; D003315:Cornea / Q000473:pathology*; D019781:Corneal Topography / Q000295:instrumentation*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D007640:Keratoconus / Q000145:classification / Q000175:diagnosis*; D008297:Male; D011446:Prospective Studies; D015203:Reproducibility of Results; D055815:Young Adult