Photosensitive epilepsy. The electroretinogram and visually evoked response

BOTH central and peripheral mechanisms may be involved in the convulsive response to photic stimulation in certain epileptics. There is disagreement as to whether the abnormal response is mediated by nonspecific (diffuse projecting system) or specific visual afferents. 1,2 The suggestion has also been made that abnormalities may exist at the retinal level because red light was a more effective stimulus than blue or green and also because closing the eyes increased photosensitivity. 3,4 The visually evoked response (VER), as measured from the scalp by an averaging device, is thought to bear some relationship to the visual pathways and to the photopic and scotopic systems. 5 Some have denied any such specificity except for perhaps the earliest component of the VER. 6,7 An increase in the VER has been reported in photosensitive epileptics, especially of the later waves. 8 The electroretinogram is a measure of retinal excitability which might