EVOKED RESPONSE IN VISUAL DISORDERS *

The observation of alterations in retinal response to photic stimulation in patients with photoreceptor pathology (Karpe, 1945), suggests that macropotentials occurring in response to photic stimulation might be altered throughout the visual system in patients with visual disorders. Although asymmetry of occipital driving in response to rhythmic photic stimulation was reported in patients with homonymous hernianopia by Weil and Nosik (1952), and Pampiglione (1952), the specific visual evoked response (m) cannot be reliably observed in the scalp EEG. Monnier (1952) observed the early components of the VER using special recording techniques, and CigLnek ( 1961 ) has extensively studied the VER in normal subjects, using Dawson’s (1947) superimposition technique. Use of an average response computer for selecting the evoked response from background EEG activity (Barlow, 1957) permits the routine observation of the average visual evoked response ( W R ) in scalp recording from conscious human subjects. Vaughan and Katzman (1962) reported characteristic changes in the early components of the VER in patients with homonymous field defects. These observations were confirmed by Cohn (1962) and studied more extensively in terms of severity of defect and method of clinical assessment by Vaughan, Katzman, and Taylor (1963). It was found that the most reliable indicator of homonymous visual defects wasdepression in amplitude of the first positive deflection (wave 11) of the VER which occurs with a peak latency between 45 and 60 msec. in normal subjects. Although some asymmetry in this wave was seen in normals and patients with unilateral brain damage without visual involvement, a highly significant ( p <.OOl) amplitude asymmetry was found in the group of hemianopic patients. By utilizing 50 per cent amplitude depression of wave I1 as a cutoff criterion, individual hemianopic patients could be distinguished from normals at the one per cent level of confidence. Simultaneous recording of average electroretinogram ERG recorded from the eyelids using conventional electrodes and VER recorded from scalp overlying the lateral occipital region provides objective electrical indices of photically induced response of retinal receptors and visual cortex. If reliable correlations of average evoked response with clinical and pathological evidence of specific types of visual disorder are obtained, objective evaluation of sensory function in man, utilizing a simple and convenient clinical technique, is possible.