Insights into the Farnsworth D15 test and its efficacy in occupational protocols

Abstract

AbstractSince their introduction, occupational colour vision (CV) standards have, in many ways, driven the development of CV tests. One test designed for occupational use is the Farnsworth D15 and despite having been introduced over 70 years ago, this test continues to be used to determine occupational suitability. To complete the test subjects are required to place 15 caps in order so as to minimise perceived differences between adjacent caps when illuminated with daylight (D65). Both red‐green (RG), yellow‐blue (YB) colour and luminance signals can contribute to what a subject perceives as a minimum difference between adjacent caps. The D15 aims to fail all monochromats, dichromats and subjects with severe anomalous trichromacy whilst passing all normal trichromats and only the least severe subjects with colour vision deficiency (CVD). The purpose of this study was to investigate the D15 test and its efficacy in occupational protocols. The different signals rod monochromats, dichromats and subjects with normal CV make use of most when presented with the D15 test were established, along with reliable D15 statistics for normal, deutan and protan subjects. A model was also developed to predict the colour signals involved, and the expected cap orders generated when subjects with a range of CVD carry out the test. When no crossings and up to two adjacent transpositions are allowed on the D15 test, 100% of normal trichromats (N = 95), 56% of deutans (N = 325) and 47% of protans (N = 170) 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). As one would expect the pass rate can vary significantly under different occupational protocols. As predicted by the model, rod monochromats, deuteranopes and protanopes were able to complete the Farnsworth D15 test when the caps were separated into two groups, despite severe loss or even complete absence of colour vision.