title: The performance of four different corneal topographers on normal human corneas and its impact on orthokeratology lens fitting.
abstract: OBJECTIVE
  To evaluate the performances of Humphrey Atlas 991, Orbscan II, Dicon CT200, Medmont E300 on young Chinese adults.
  
  
  METHODS
  Three sets of corneal topography measurements were obtained from each topographer from 22 subjects-two sets by the same examiner and one set by another examiner on the same day.
  
  
  RESULTS
  There were no significant within-examiner and between-examiner differences for any of the parameters tested for each topographer. However, only the repeatability and reproducibility (of apical radius[Ro], eccentricity, and elevation) of the Humphrey and Medmont were good. There was no statistically significant between-topographer difference in R(o), but significant differences in eccentricity and elevation values were found. The number of repeated readings that should be taken for a precision of 2 microm (elevation) were 12 for the Humphrey and 2 for the Medmont.
  
  
  CONCLUSIONS
  The performance of both the Humphrey and the Medmont was very good. R(o) and eccentricity values of different topographers cannot be used interchangeably, but the agreement in elevation values was good for these topographers. The number of repeated readings required for maximum precision varies with the topographer used, and they are not interchangeable.
authors.affiliation: Centre for Myopia Research, Department of Optometry and Radiography, The Hong Kong Polytechnic University, HKSAR, China. orpaulin@polyu.edu.hk
authors.forename: Pauline
authors.initials: P
authors.lastname: Cho
authors.forename: Andrew K C
authors.initials: AK
authors.lastname: Lam
authors.forename: John
authors.initials: J
authors.lastname: Mountford
authors.forename: Larry
authors.initials: L
authors.lastname: Ng
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D019781:Corneal Topography / Q000295:instrumentation*; D004867:Equipment Design; D006801:Humans; D015588:Observer Variation; D015203:Reproducibility of Results