visual evoked potentials

Visual evoked potentials (VEPs) are small cortical potentials elicited by visual stimuli and recorded from electrodes on the patient's scalp. A VEP is on the order of 5 μV and sits within an electroencephalogram of about 60 μV.¹ Many responses are therefore averaged to produce an accurate reading.² The VEP shows whether the visual system is intact from retina to visual cortex, but the test says nothing about what the patient perceives.²

The stimulus is a flash or a pattern, typically a phase-alternated checkerboard or grating.^2,3 Patterned VEPs detect minor visual pathway abnormalities with greater accuracy and sensitivity than flash VEPs.² A lesion in the afferent visual pathway makes the VEP abnormal.³ Macular, optic nerve and cortical lesions can all reduce VEP amplitude, so the VEP can establish a deficit without localizing the lesion.¹ In optic neuritis, VEP latency increases in the affected eye and may stay prolonged after acuity improves.¹