Visual Discomfort and Visual Function: Colour and Contrast

In six studies, vision and visual discomfort were investigated in individuals who experienced migraine or reading difficulty. Contrast discrimination thresholds were measured at two pedestal contrasts (10% and 50%) in volunteers with migraine with aura (MA), without aura (MO) and controls (C).There was no significant difference in thresholds between groups, although participants with unilateral aura had superior discrimination thresholds in the visual field affected by the aura. Similar groups of volunteers viewed gratings illuminated by light of a colour previously selected as “comfortable” or “uncomfortable” for viewing text. They viewed gratings of increasing contrast until discomfort occurred. The thresholds were lower in MA and MO groups and the “comfortable” colour of lighting raised the contrast at which discomfort was reported. In a further group of volunteers the “comfortable” colour raised the contrast discrimination thresholds. The visual evoked potential and haemodynamic response to gratings with low,mid and high contrast was measured in MA and C groups. There were no differences between groups, although the amplitude of the N2 component increased with contrast. Schoolchildren who habitually used a coloured overlay to read selected a colour of light comfortable for viewing text. Reading speed was no greater with lenses that matched the chosen colour. The study was repeated with patients attending Anglia Ruskin Visual Stress Clinic and patients read more quickly with the appropriate tint under double-masked conditions.The above findings are interpreted in terms of cortical hyperexcitability.