Thresholds for detection of a target against a background grating suggest visual dysfunction in migraine with aura but not migraine without aura.

Square-wave gratings with particular spatial characteristics induce visual illusions. Patients with migraine are particularly susceptible to these illusions and report discomfort. Their discomfort tends to be greater when the gratings are illuminated by red light, a tendency not shown by controls. Gratings that induce illusions have been found to impair the recognition of optically superimposed targets in headache-free control subjects. We measured the impairment of target detection under illuminants of various chromaticities in migraineurs with and without aura and in matched controls. Migraineurs with aura had significantly higher thresholds for target detection than either migraineurs without aura or controls; in addition, the effect of chromaticity was slightly more pronounced in both migraine groups than in the control group. These findings are consistent with a recent suggestion that migraine with aura might give rise to subclinical damage to the primary visual cortex.