The main purpose of this study was to produce reliable, color assessment outcomes to examine the extent to which single and multi-test protocols in use meet current clinical and occupational needs. The latter include the detection of small changes in chromatic sensitivity as the earliest signs of retinal and/or systemic disease, and the need to assess the class of color vision in congenital deficiency and to quantify severity of loss. Color vision was assessed using Ishihara (IH), Farnsworth Munsell D-15, City University (CU, 2nd ed.) and Holmes-Wright type A (HW-A) lantern tests. All subjects also carried out Colour Assessment and Diagnosis and Nagel anomaloscope tests. The sample included 350 normal trichromats, 1012 deutans and 465 protans (age 31.1 ± 12.4, range 10-65 years). The results reveal the trade-off between sensitivity and specificity, depending on the number of errors accepted as a pass on the IH test. The D-15 and CU tests pass all normals and almost 50% of subjects with color vision deficiency. The HW-A lantern passes all normals, 22% of deutans and 1% of protans. The multi-test protocols designed to identify protans and to pass only subjects with mild color loss, pass over 50% of protans and deutans. Many of the subjects who fail exhibit less severe loss of color vision than others who pass. When high sensitivity for detection of congenital deficiency is achieved, single-test protocols fail many normal trichromats. Multi-test protocols produce large variability and fail to achieve desired aims.

Color vision tests and multi-test protocols in current use often fail to detect small changes in red/green (RG) and yellow/blue (YB) color vision due to poor sensitivity. The tests also have low specificity. In this study, we examine how improved understanding of within-and inter-subject variability in RG and YB color vision and accurate assessment of the differences in color thresholds between the least-sensitive, age-matched normal trichromats, and the leastaffected deutans and protans can be used to design an efficient color vision screener (CVS) test. To achieve this objective, we examined two extensive data sets from earlier studies and carried out new experiments to provide better estimates of within-subject variability in color thresholds and to validate the CVS test. The data sets provide essential information on inter-subject variability, the effects of normal aging on RG and YB thresholds, and the spread in RG color thresholds in deutan and protan subjects. A statistical model was developed to optimize the parameters of the CVS test and to predict the limits of what can be achieved in color assessment. The efficiency and repeatability of the CVS test were then assessed in 84 subjects. The results match model predictions and reveal close to 100% test efficiency. The test takes between

The Farnsworth D-15 test (D-15) is commonly used to screen for moderate to severe congenital color vision deficiency. The aim of this study was to establish reliable D-15 statistics for normal, deutan and protan subjects, and to investigate the different visual signals one can use to carry out the test, even in dichromats and rod monochromats. Six hundred and seventy-four subjects were examined using the D-15, the Colour Assessment and Diagnosis test and the Nagel anomaloscope. A rod monochromat and five dichromats were tested using the standard D-15 protocol before the caps were separated into two groups and subjects were asked to repeat the task. D-15 spectral radiance data, measured under D65 illumination, were used to estimate differences in photoreceptor excitations for each of the caps. When no crossings and up to two adjacent transpositions on the D-15 results diagram are accepted as a pass, 100% of normal trichromats, 54% of deutans and 43% of protans pass the D-15. A rod monochromat and two protanopes and deuteranopes were able to complete the D-15 when the caps were separated into two groups, despite severe loss or even complete absence of color vision. When up to two adjacent transpositions are accepted 50% of color deficient subjects, some with severe red/green loss, pass the D-15. While the D-15 is normally used to screen for moderate to severe color deficiency, subjects with severe loss can still use combined, residual red/green, yellow/blue and luminance signals to pass.

Since 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.

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.