title: Eccentricity and measurement variability and repeatability with the retinal thickness analyser.
abstract: OBJECTIVE
  To define the variability and repeatability of retinal thickness measurements using the retinal thickness analyser (RTA) and to elucidate any interaction between eccentricity (that is, position relative to the fovea) and variability and repeatability.
  
  
  METHODS
  The sample comprised 20 normal subjects of mean age 33 years. Each subject attended for two visits. Repeated RTA scans were acquired centred on the fovea and for any one of the four possible non-foveal scan areas. The mean retinal thickness (+SD) was calculated for a series of concentric circular bands centred on fixation. A repeated measures analysis of variance (ANOVA) was used to determine any significant interaction between the variability of RTA thickness values and eccentricity.
  
  
  RESULTS
  The group mean coefficient of variation and coefficient of repeatability were highest at the fovea. The repeated measures ANOVA revealed that the within test variability of RTA measurements varied significantly with eccentricity (p<0.0001). Similarly, the between test repeatability varied significantly with eccentricity (p = 0.045).
  
  
  CONCLUSIONS
  The significantly elevated within test variability and between test repeatability in the foveal area need to be considered when using the RTA to evaluate patients with macular disease.
authors.affiliation: Department of Ophthalmology and Vision Science, Toronto Western Hospital, University of Toronto, Toronto, M5T 2S8 Ontario, Canada.
authors.forename: E D
authors.initials: ED
authors.lastname: Gilmore
authors.forename: C
authors.initials: C
authors.lastname: Hudson
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D003941:Diagnostic Techniques, Ophthalmological; D005584:Fovea Centralis / Q000033:anatomy & histology; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D018613:Microscopy, Confocal; D008875:Middle Aged; D010781:Photography; D012016:Reference Values; D015203:Reproducibility of Results; D012160:Retina / Q000033:anatomy & histology*