  The aim of this study was to assess the extreme effects of tinted lenses on
colour vision by examining changes in chromatic sensitivity when viewing visual
displays through a slightly tinted (blue-blocking) filter and through a heavily
tinted, orange coloured filter. The CAD test was used to measure both red/green
(RG) and yellow/blue (YB) chromatic sensitivity in ten subjects when viewing
visual displays through each of the two filters. The measured RG and YB colour
thresholds were then compared with similar measurements made without coloured
filters in front of the eye. The blue-blocking filter absorbs only a small
amount of short-wavelength light whilst the orange filter attenuates
preferentially more short wavelength and some middle-wavelength light. The
results show that the blue-blocking filter does not affect significantly either
RG or YB colour vision. The orange filter, on the other hand, causes large
changes in colour discrimination. The results were analysed statistically by
comparing results obtained with the coloured filters with those measured
without any filters in front of the eye. More experimental work is now needed
to establish how much short wavelength light can be removed without affecting
significantly the subject's colour discrimination performance.
