title: Repeatability of corneal and ocular aberration measurements and changes in aberrations over one week.
abstract: BACKGROUND
  Both Shack-Hartmann aberrometry (IRX3, Imagine Eyes, Orsay, France) and Scheimpflug photography (Oculus Pentacam, Oculus Inc Wetzlar, Germany) are known to provide repeatable measurements. The variability in measurements of corneal and ocular aberrations obtained with these instruments over one week had not been assessed. The aim was to study the variability in corneal and ocular aberrations in the human eye over one week and to determine the impact of age on corneal and crystalline lens aberrations and on the variability of these measurements.
  
  
  METHODS
  Monochromatic ocular aberrations were measured with the IRX3 and monochromatic corneal aberrations were measured using Scheimpflug photography on one eye of 23 normal subjects at periods of a few seconds, one hour and one week after the initial measurement.
  
  
  RESULTS
  No significant differences were found between the initial aberrations and aberrations measured at 59 +/- 24 seconds, 1.10 +/- 0.24 hours and 7.11+/- 0.31 days later. Analysis with Bland and Altman plots showed that measurements with both instruments were highly repeatable over the times studied. There was no relationship between age and the variance of corneal and ocular aberrations (higher order, spherical and coma aberrations). Corneal spherical aberration did not show a significant correlation with age, whereas the lens aberrations changed from being negative in the younger age groups to positive in the older age group, however, these differences failed to reach statistical significance (p > 0.05).
  
  
  CONCLUSIONS
  The variability found in all the measurements was small and not clinically significant and could be attributable to instrument noise, changes in the tear film and to small fixational eye movements.
authors.affiliation: Faculty of Life Sciences, The University of Manchester, United Kingdom. marco.miranda@postgrad.manchester.ac.uk
authors.forename: Marco A
authors.initials: MA
authors.lastname: Miranda
authors.forename: Clare
authors.initials: C
authors.lastname: O'Donnell
authors.forename: Hema
authors.initials: H
authors.lastname: Radhakrishnan
mesh_terms: D000065:Accommodation, Ocular; D000293:Adolescent; D000328:Adult; D016477:Artifacts; D019781:Corneal Topography / Q000295:instrumentation* / Q000592:standards*; D005260:Female; D005403:Fixation, Ocular; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009907:Optometry / Q000295:instrumentation*; D011446:Prospective Studies; D012030:Refractive Errors / Q000175:diagnosis* / Q000503:physiopathology*; D015203:Reproducibility of Results; D013666:Tears; D055815:Young Adult