The results suggest that supplementation with L or Z increases MPOD at the fovea and at 2.5 degrees , and that supplementation can improve CATs at high mesopic levels and hence visual performance at low illumination.
Normal trichromatic colour vision (CV) is often required as a condition for employment in visually demanding occupations. If accurate CV tests were available Q2 to enforce this requirement, a significant percentage of subjects with anomalous, congenital trichromacy who can perform the suprathreshold, colour-related tasks encountered in many occupations with the same accuracy as normal trichromats would fail. These applicants would therefore be discriminated against unfairly. One solution to this problem is to produce minimum, justifiable CV requirements that are specific to each occupation. This has been done successfully for commercial aviation (i.e. the flight crew) and for Transport for London train drivers. An alternative approach is to make use of new findings and the statistical outcomes of past practices to produce graded, justifiable CV categories that can be enforced. To achieve this aim, we analysed colour assessment outcomes and quantified severity of CV loss in 1363 subjects. The severity of CV loss was measured in each subject and statistical, pass/fail outcomes established for each of the most commonly used, conventional colour assessment tests and protocols. This evidence and new findings that relate severity of loss to the effective use of colour signals in a number of tasks provide the basis for a new colour grading system based on six categories. A single colour assessment test is needed to establish the applicant's CV category which can range from 'supernormal', for the most stringent, colour-demanding tasks, to 'severe colour deficiency', when red/ green CV is either absent or extremely weak.
YB thresholds remain unaffected by supplementation with lutein and/or zeaxanthin rather, at increased MPOD levels, RG vision tends to be improved. The model accounts for the absence of correlation between MPOD and YB thresholds and predicts a marginal improvement in RG discrimination when MPOD is high.
These findings suggest that accurate measurements of RG and YB colour thresholds can provide a sensitive measure of functional change in diseases of the retina with patterns of loss that differ significantly in AMD and diabetes.
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