Background: Both yellow-blue (YB) discrimination thresholds and macular pigment optical density (MPOD) measurements in the eye exhibit large variability in the normal population. Although it is well established that selective absorption of blue light by the macular pigment (MP) can significantly affect trichromatic colour matches, the extent to which the MP affects colour discrimination (CD) sensitivity remains controversial.
Objective: In this study, we assess whether the variability in YB thresholds is attributable to differences in MPOD, both at the fovea and in the paracentral visual field. We also investigated whether higher levels of MP offer any advantage in other visual functions such as red-green (RG) CD sensitivity.
Design: CD thresholds and spatial MPOD profiles were measured in 24 normal trichromats supplemented with zeaxanthin (OPTISHARP) and/or lutein. Novel stimulus conditions that isolate YB and RG chromatic mechanisms were employed and MPOD profiles were measured up to an eccentricity of 8 degrees.
Results: The data reveal an increase in MPOD in the supplemented subjects that was almost uniform within a centre region around the fovea subtending +/-4 degrees. RG sensitivity was high in all subjects with thresholds well within the normal range. Unexpectedly, YB thresholds were also normal and showed no correlation with MPOD. A model for threshold CD based on appropriate combinations of cone contrast signals was developed to explain the experimental findings.
Conclusions: 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.