title: Reliability and validity studies of a new computer-assisted crossed-cylinder aberroscope.
abstract: OBJECTIVE
  We assessed the reliability and validity of a new computer-assisted crossed-cylinder aberroscope technique which measures the monochromatic optical aberrations of the human eye.
  
  
  METHODS
  Intra-image variability, the variability occurring when the same image is repeatedly measured, and inter-image variability, the variability occurring when different images collected from the same eye are measured, were assessed using 10 repeated measures on each of 10 different subjects. We compared the measurements made using the computer-assisted technique with manual measurements made when a human operator performed all the aberroscope grid intersection location tasks.
  
  
  RESULTS
  One-way repeated measures analyses of variance (ANOVA) on the inter-image and intra-image variability showed that the mean of the measurements made was statistically independent of the occasion on which a group of subjects was measured, and inter-image variability was larger than intra-image variability. A two-way repeated measures ANOVA comparing computer-assisted results with manual results showed that the means of the measurements made with the two methods are not statistically different from one another. The manual results showed greater variability than computer-assisted measurements.
  
  
  CONCLUSIONS
  The technique is reliable and valid compared to earlier objective crossed-cylinder aberroscopic techniques.
authors.affiliation: Department of Optometry, University of Bradford, West Yorkshire, United Kingdom. M.Cox@bradford.ac.uk
authors.forename: M J
authors.initials: MJ
authors.lastname: Cox
authors.forename: G
authors.initials: G
authors.lastname: Walsh
mesh_terms: D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D009799:Ocular Physiological Phenomena; D012029:Refraction, Ocular; D015203:Reproducibility of Results; D014741:Video Recording; D014787:Vision Tests / Q000295:instrumentation*; D014785:Vision, Ocular / Q000502:physiology*