Abstract
The neurophysiological response of the visual system, from the pre-synaptic function of the retina to occipital cortex, of 45 "classic" migraine and 27 normal control subjects, with age range 15-55 years was studied using different forms of visual stimuli. The aims were to determine the nature and identify the site of differences between migraine and control subjects and to find out whether the differences were due to a constitutional predisposition to migraine or a were consequence of migraine attacks. Preliminary experiments on eight subjects determined the operational techniques, electrode montage, reference sites and frequency range of flicker stimulation. Recordings included the electro-oculogram during dark and light adaptation, the electro-retinogram and visual evoked potential to single and repetitive stroboscopic flash at rates from 4 to 80 per second and the visual evoked potential to pattern reversal (checkerboard) presented as full and half field stimulation. Cross-group comparisons were made according to age, sex, length of history and frequency of attacks. Recordings of retinal function were similar in the control and migraine groups. However, the visual evoked potentials to single flash, repetitive flash and checkerboard stimulation showed statistically significant differences between the groups indicating that cerebral visual function is different in people suffering from migraine especially if they are female. The differences between the groups are discussed in relation to the concept of subsystems of the visual system. It is concluded that any dysfunction occurs late, probably in the cortex, in the medium frequency subsystem to flicker whilst the delays in the pattern reversal subsystem reflect physiological dysfunction rather than structural anomaly. Furthermore, it is concluded that the differences are associated with a constitutional predisposition to migraine and not to trauma from cerebral ischaemia suffered during migraine attacks.