title: Measurement repeatability of corneal aberrations.
abstract: OBJECTIVE
  Customized procedures that aim to improve visual performance beyond traditional sole correction of sphere and cylinder require the reliable determination of higher order corneal and ocular aberrations for individual eyes. The aim of the current investigation was to determine the repeatability of corneal aberration measurement.
  
  
  METHODS
  Ten subjects were measured on 10 different days using a videokeratoscope. The Zernike coefficients and the wavefront error were calculated from the height data files using CTView. Repeatability was calculated for apertures of 3, 4.5, and 6 mm at the 95% confidence level.
  
  
  RESULTS
  The wavefront error absolute repeatability was similar for the 4th and 10th order analysis. The absolute repeatability for individual Zernike coefficients was coefficient dependent; the poorest repeatability was recorded for coma-like aberrations (uncertainty 3 mm = 0.060 microm; 4.5 mm = 0.083 microm; 6 mm = 0.109 microm). The relative repeatability compared to the population means was good for wavefront error (5% to 20%) but poor for some individual Zernike coefficients.
  
  
  CONCLUSIONS
  Videokeratoscope clinical repeatability was sufficient to reliably determine wavefront error at a single session, but may require several examinations and/or repeated independent measurements at the same examination to determine reliably some Zernike coefficients. This has significant practical implications for accurate customized correction of aberrations.
mesh_terms: D000328:Adult; D003315:Cornea / Q000473:pathology*; D003316:Corneal Diseases / Q000175:diagnosis*; D019781:Corneal Topography; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results