title: Extent of foveal tritanopia in diabetes mellitus.
abstract: OBJECTIVE
  To use a colour matching technique to test the hypothesis that the foveal tritanopic zone is increased in size in diabetes mellitus.
  
  
  METHODS
  A Wright tristimulus colorimeter was adapted for small field colour matching and colour matches were performed on bipartite fields in the range 12' to 60' of arc. The reference stimulus was 490 nm desaturated with 650 nm and the matching stimulus consisted of either two wavelengths (530 nm and 650 nm) or three (460 nm, 530 nm, and 650 nm). The size of the zone of foveal tritanopia was measured using two alternative forced choice presentations of dichromatic and trichromatic matches made by the observer for different field sizes. 21 diabetic and 12 controls performed the experiment.
  
  
  RESULTS
  The results for the controls show a normal distribution, with a median foveal tritanopic zone of 18' of arc. The median for the diabetic patients was also 18' of arc, but the distribution showed a significant skew to the right. A non-parametric test shows a significant difference in comparison with the controls (p = 0.01), with several subjects having extensive zones of foveal tritanopia, reaching up to 1 degree.
  
  
  CONCLUSIONS
  In the majority of diabetic subjects the extent of foveal tritanopia is normal; however, there is good evidence that in a small number of subjects the size of the zone is significantly increased. This indicates S-cone pathway damage that is sufficiently severe to lead to dichromatic colour vision in the fovea.
authors.affiliation: Vision Research Group, Biophysics, Imperial College, South Kensington, London SW7 2BZ, UK. family.davies@ukgateway.net
authors.forename: N
authors.initials: N
authors.lastname: Davies
authors.forename: A
authors.initials: A
authors.lastname: Morland
mesh_terms: D000328:Adult; D000368:Aged; D003119:Color Perception Tests; D003117:Color Vision Defects / Q000209:etiology* / Q000473:pathology; D003930:Diabetic Retinopathy / Q000150:complications* / Q000473:pathology; D005584:Fovea Centralis; D006801:Humans; D008875:Middle Aged; D015999:Multivariate Analysis; D017949:Retinal Cone Photoreceptor Cells