An assessment of the ‘mesopization’ model of blue-yellow colour vision defects

Abstract

The colour-vision losses in blue-yellow acquired colour-vision deficiencies have been likened to the performance of normal subjects at low luminance levels and described as a ‘mesopization’. The B-Y colour-vision deficiency seen in diabetic patients has been shown to be enhanced when short-duration stimuli are used in patients without retinopathy (Scase et al., 1990). To assess whether mesopization can also explain losses with brief stimuli, hue-discrimination performance was determined along the cardinal directions of colour space in subjects with normal colour vision over a range of luminances from 7.0 to 0.025 cd m^-2. Stimuli were presented on a colour video-display system. This technique has the advantage, unlike the Farnsworth-Munsell 100-Hue Test on which the mesopization hypothesis was based, of having no possible bias towards B-Y thresholds compared with red-green thresholds when screen luminance was reduced. This was true for both long- and short-duration stimuli. Therefore mesopization cannot account for the specific deficits in B-Y discrimination previously demonstrated by this technique in diabetic patients, especially those found with short-duration stimuli in patients without retinopathy. A specific loss in blue-yellow processing is indicated.