title: Repeatability of ocular aberration measurements in patients with keratoconus.
abstract: OBJECTIVE
  To explore the repeatability of lower-order and higher-order ocular aberrations measured in patients with keratoconus.
  
  
  METHODS
  The IRX-3 (Imagine Eyes, Paris, France) aberrometer was used to record lower-order and higher-order aberrations in 31 eyes of 31 patients with keratoconus. Four monocular measurements were taken consecutively for each patient. The aberrometry data were analysed up to the 5th Zernike order for a 4-mm pupil diameter. The data were evaluated using repeated-measures anova and Friedman analyses. Repeatability was analysed using within-subject standard deviation (S(W) ) and the repeatability limit (r) calculated as 1.96 ×√2 × S(w).
  
  
  RESULTS
  Of the 11 aberration terms evaluated, the repeatability of Z (2,0) (mean = 1.36 μm; S(W) = 0.09 μm; r = 0.26 μm); Z (2,±2) RMS (mean = 1.05 μm; S(W) = 0.09 μm; r = 0.24 μm) and Z (4,0) aberrations (mean = 0.34 μm; S(W) = 0.09 μm; r = 0.24 μm) showed the highest variability. In contrast, Z (3,±1) RMS aberrations (mean = 0.85 μm; S(W) = 0.06 μm; r = 0.16 μm) and Z (4,±2) RMS aberrations (mean = 0.40 μm; S(W) = 0.07 μm; r = 0.18 μm) showed comparatively better repeatability.
  
  
  CONCLUSIONS
  The lower-order and higher-order aberrations measured in this group of keratoconic patients showed higher levels of variability compared to previous investigations of visually-normal subjects. These results may be of interest to eyecare practitioners involved in the design and fitting of aberration-controlling contact lenses for patients with keratoconus.
authors.affiliation: Faculty of Life Sciences, The University of Manchester, Manchester, UK.
authors.forename: Amit
authors.initials: A
authors.lastname: Jinabhai
authors.forename: Hema
authors.initials: H
authors.lastname: Radhakrishnan
authors.forename: Clare
authors.initials: C
authors.lastname: O'Donnell
mesh_terms: D057128:Aberrometry; D000328:Adult; D000704:Analysis of Variance; D003315:Cornea / Q000503:physiopathology*; D019781:Corneal Topography / Q000379:methods; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D012029:Refraction, Ocular / Q000502:physiology; D015203:Reproducibility of Results; D055815:Young Adult