Assessing the severity of colour vision loss - implications for occupational environments

Colour is often used in safety‐critical environments to code and signal information. Colour is also used to enhance target ‘conspicuity’ and visual performance in ‘grouping’, segmentation and pop‐out tasks. Colour vision (CV) is not a key requirement in everyday life, but in some safety‐critical jobs, it can be a matter of life and death. The absence of normally functioning chromatic mechanisms leads to reduced chromatic sensitivity and also to changes in the perceived colour of objects. CV is needed in some occupations, but the majority of subjects with congenital colour deficiency (CCD) retain some red / green (RG) CV. When the latter is combined with normal, yellow / blue (YB) colour signals, many CCD subjects are able to carry out suprathreshold, colour‐related tasks as well as normal trichromats. Since severity of loss in congenital deficiency extends from almost normal to complete absence of CV, it is important to determine accurately severity of CV loss. Empirical studies carried out in some occupations established the degree of CV loss that can be classed as ‘safe’. This led to the establishment of minimum requirements that can be enforced. In addition to safety, the overall aim is to ensure that all subjects with anomalous trichromatic colour vision who can perform the safety‐critical, colour tasks in a given job as well as normal trichromats pass and do not end up being discriminated against unfairly on the basis of their CCD. Until very recently, it has not been possible to achieve this aim, simply because many existing CV tests lack sensitivity and / or specificity and also fail to quantify reliably the severity of CV loss. Improved understanding of CV and the recent development of sensitive and specific CV tests have transformed traditional colour assessment (Br Med Bull. 2017;122 (1):51–77). Results will be presented to show how a single colour assessment test can be used to establish the applicant’s class of CV and to quantify the severity of loss.