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Benjamin Edward William Evans, Marisa Rodriguez-Carmona, John L Barbur; Analysis of the residual signals colour deficients can use to pass the D-15 test. Invest. Ophthalmol. Vis. Sci. 2019;60(9):1306.
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© ARVO (1962-2015); The Authors (2016-present)
The Farnsworth D15 panel test when illuminated with daylight (D65) requires the subject to order 15 coloured surfaces so as to minimise the perceived differences between adjacent caps. The 15 caps exhibit only small luminance differences (when viewed by normal trichromats) and the task is reduced to finding which of the remaining caps differs least from the last selected cap. ‘Adjacent’ transpositions are indicative of reduced red / green (RG) chromatic sensitivity and ‘major’ crossings are linked to more severe loss of RG colour vision with either deutan, protan or tritan characteristics. In order to pass the 6.3% of normal trichromats that make adjacent transpositions, up to two adjacent transpositions are normally accepted as a pass. Based upon this protocol, 56% of deutans and 47% of protans also pass. The purpose of this study was to establish reliable D15 statistics for normal, deutan and protan subjects. A model was also developed to examine the residual signals colour deficients make use to pass the D15 test.
RG and yellow / blue (YB) thresholds were measured in 590 subjects (325 deutans, 170 protans and 95 normals) using the Colour Assessment & Diagnosis (CAD) test. Each subject also completed the D15 test. The spectral radiance data measured for each cap under D65 illumination were used to model the expected changes in RG, YB and the corresponding luminance signals for normal, deutan and protan subjects.
When no crossings and up to two adjacent transpositions are allowed on the D15 test, 100% of normal trichromats, 56% of deutans and 47% of protans pass. 43% of protans and 23% of the deutans that pass have RG thresholds above 10 CAD units (one CAD unit describes the mean RG colour signal strength for young normal trichromats). The model predicts large changes in YB colour signals and increased luminance differences across adjacent caps in subjects with congenital deficiency.
53% of colour deficient subjects pass the D15 test, using the protocol needed to ensure that all normal trichromats pass. Some of these subjects have severe loss of RG chromatic sensitivity. The model developed to predict this outcome shows that in the absence of adequate RG signals, subjects with congenital deficiency can use the YB and the enhanced residual luminance differences across the D15 caps to carry out the arrangement task.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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