On the Validity of Colour Vision Tests in the Field: A Practical Assessment

We found a surprisingly high incidence of tritan-like (blue - yellow) symptoms in population samples from southern Africa. However, these results could be false positives because the test (The City University Colour Vision Test: CUCVT) was not administered under the prescribed illuminant (CIE Illuminant C). We therefore assessed the robustness of the test in order to estimate the true tritan rates in our data and to assess its usefulness under field conditions. First, we administered the test to normal young people under three illuminances (600, 300, and 150 lux), and three spectral distributions (C, reduced short wavelength, and reduced long wavelength). In addition, two viewing distances were used: the standard (14 inches) and double the standard. At the normal viewing distance, no errors were induced by reducing the illuminance or by changing the spectral distribution. However, at 28 inches, both illuminance and spectral changes induced tritan errors. Second, we assessed a sample of old people (over 65), first, under the prevailing illuminant; second, under Illuminant C; and third, under Illuminant C with increased intensity. In all cases, the old people in the sample made large numbers of tritan responses, but the frequency of tritan errors decreased under Illuminant C and decreased even more under enhanced illuminance. Thus, for normal young people at the prescribed distance the test is robust, but at increased distance the test is vulnerable to deviations from the prescribed illuminant. Further, older people can present as having tritan-like problems unless the illuminance is increased above the standard.