Performance of the Ishihara, D-15, and City University Colour Vision Test as a function of intraocular straylight.

Three colour vision tests, the Ishihara test, the City University Test (CUT) and the D-15 test were studied as a function of induced intraocular straylight, using a commercially available light-scattering filter. Thirty young individuals (aged 17-28 years) with no ocular abnormalities and normal colour vision participated in the study. Intraocular straylight was estimated in all individuals using a psychophysical compensation method with the C-Quant straylight meter, with and without the light-scattering filter which caused an increase in intraocular straylight typical of that found for cataract. Under normal viewing conditions all the subjects passed each of the three tests with no errors. When viewing the Ishihara test plates through the filter, 10 out of the 30 observers made at least one error. Three subjects also made errors on the desaturated CUT test plates, but all subjects still passed the D-15 test with the filter. The errors in the Ishihara test correlated with the amount of intraocular straylight, as measured with the C-Quant. This study indicates that interpretation of the Ishihara test in a clinical environment will be made more difficult in individuals with higher levels of straylight.Introduction.