title: A comparative study of the performance of different corneal topographers on children with respect to orthokeratology practice.
abstract: OBJECTIVE
  The purpose of this study was to evaluate and compare the performance of three topographers, Medmont E300, Keratron Scout, and Humphrey Atlas 991, for the measurement of corneal parameters of interest in orthokeratology practice on young children.
  
  
  METHODS
  Apical radius (R0), flattest corneal curvature (flat k), eccentricity (e) value, and elevation at 9-mm chord were measured twice on 22 healthy subjects of mean +/- standard deviation (SD) age 11.2 +/- 2.2 years using the topographers under investigation.
  
  
  RESULTS
  The repeatability of the Medmont and Humphrey were good for the measurements of R0 and flat k. The repeatability of the Humphrey was also good for the measurement of e-value. However, for both topographers, the measurement of elevation was not precise enough for orthokeratology empirical lens design. The Keratron showed poor repeatability for all the parameters evaluated. The agreement of the parameters of interest between these instruments was poor.
  
  
  CONCLUSIONS
  The Medmont and the Humphrey showed good repeatability on children, but the precision of elevation measurements was not good enough to be used for designing empiric orthokeratology lenses on children. The Keratron is not recommended to be used on children in orthokeratology fitting and management. Interinstrumental agreements were significantly different and therefore measurements from different topographers should not be used interchangeably.
authors.affiliation: Centre for Myopia Research, Department of Optometry & Radiography, The Hong Kong Polytechnic University, HKSAR, China.
authors.forename: Wan Sang
authors.initials: WS
authors.lastname: Chui
authors.forename: Pauline
authors.initials: P
authors.lastname: Cho
mesh_terms: D002648:Child; D003261:Contact Lenses; D003315:Cornea / Q000473:pathology*; D019781:Corneal Topography / Q000592:standards*; D005260:Female; D006801:Humans; D008297:Male; D009216:Myopia / Q000628:therapy*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity