The spectral content of the light reflected from objects carries useful information about their chemical composition and surface properties. This can often be of advantage and the perception of ‘colour’ has evolved as important attribute of vision to achieve this aim. ‘Colour’ vision (CV), is of great value in enhancing our visual performance since it enables us to represent and use effortlessly information carried in the spectral composition of the light.
Not all of us benefit from normal CV and although colour perception is not a key requirement in everyday life, in some safety-critical jobs, it can be a matter of life and death. The correct interpretation of air traffic landing lights, railway signals and electrical wiring is a safety-critical task for which good colour perception is vital.
Normal trichromatic CV relies on the normal functioning of L, M and S cones. Some subjects do not have three functioning cone types or in some cases rely on pigments that differ in spectral responsivity to those found in normal trichromats. Congenital RG colour deficiency affects ~ 8% of men and less than 1% of women. The presence of anomalous red / green (RG) or yellow / blue (YB) signals leads to reduced chromatic sensitivity as well as changes in the perceived colour of objects. Many subjects with anomalous, trichromatic CV can still make use of their residual RG signals and their normal YB vision to perform the suprathreshold, colour-related tasks encountered in safety-critical, working environments as well as normal trichromats. Since these subjects should not be discriminated against on the basis of their colour deficiency, recently it has become more important to improve the sensitivity and specificity of our tests, and in particular, the ability to quantify accurately the severity of CV loss.
Recent advances in colour assessment make it possible to detect congenital / acquired deficiency with close to 100% sensitivity and specificity and, more importantly, to also quantify accurately the severity of CV loss. The Colour Assessment and Diagnosis (CAD) test achieves these aims, but the fully calibrated equipment needed is expensive and the full test requires ~ 14 minutes to complete. The development of a rapid, sensitive and inexpensive CV screener that can be administered quickly and efficiently would solve these problems. If such a screener was available for use within schools and visually demanding occupations, only ~10% of male subjects would require full colour assessment to establish accurately the class of deficiency and severity of loss.
A new CAD-Screener developed to fulfil these requirements will be described. The screener takes just under three minutes to complete. Only ~ 3.8% of the least affected deutans pass. All normal trichromats and all protans are detected with 100% sensitivity and specificity. Further work is needed to make the CAD-Screener available on the web and to extend its use in schools and occupations.