Visual Evoked Potential Pesponses in Focal Lesions of the Visual Pathway

ABSTRACT

A visual stimulus elicits a complicated series of potentials from the human cortex. The visual evoked potential test has advantages in detecting lesions that alter electrophysiology but do not produce detectable alterations of radiodensity, displace surrounding structures or change vascular supply. A sequence of four wave component(I, II, III, IV) that occured in the 100 msec following the flash stimulation can be recorded from scalp electrodes in 20 patients with focal lesions of the visual conducting system using computer averaging techniques. 1) 20 patients presenting with visual symptoms were classified as four groups according to the locations of the lesions in visual pathway : optic nerve lesion(8 cases), chiasmatic lesion(5 cases), optic tract or radiation lesions(4 cases) and visual cortical lesion(3 cases). 2) In optic neuritis, wave patterns of VEP was suppressed markedly in I(P30~40 msec) and II(N50~60 msec) wave components and in the optic nerve injuries, flat wave patterns were noted. 3) In chiasmatic lesions, VEP showed mild prolongation of latency(wave II, N50~60 msec) throughout and mild supperssion of the amplitudes of the wave components presented. On stimulation of one eye, latency and amplitude of the contralateral sided eye were markedly delayed and suppressed. 4) VEP of optic tract and optic radiation lesions showed marked prolongation and suppression of wave pattern in late components(wave II, III). In multiple sclerosis, VEP abnormality was presented in early state(N80~90 msec). 5) In the visual cortical lesions, the wave patterns of the VEP were almost symmetrically flat on both side. Serial evaluation of the VEP could provide good information for the evaluation of visual pathway lesions and functional recovery marker.