Vep

Visual evoked potential (VEP) is the electrical response generated by the visual cortex in response to visual stimulation, measured with electroencephalography (EEG). It reflects the functional integrity of the visual pathways from the retina through the optic nerve to the occipital cortex. The most prominent early component in pattern-stimulus paradigms is the P100, which occurs around 100 milliseconds after stimulus onset.

Recording typically uses scalp electrodes arranged with an active electrode over the occipital cortex (such as Oz or O1/O2), a reference electrode at a frontal site, and a ground electrode. Stimuli include pattern-reversal checkerboards or flash stimuli presented at controlled luminance and contrast. The EEG signals are averaged across many trials to yield a reliable waveform and improve the signal-to-noise ratio. VEP testing is often performed with high-contrast stimuli and standardized stimulus parameters, with results interpreted relative to age-matched normative data.

Interpretation focuses on the latency and amplitude of major components, especially the P100. Prolonged P100 latency can indicate demyelination or optic nerve dysfunction, while reduced amplitude may reflect reduced signal strength from transmission abnormalities or media opacities. Normal latency with reduced amplitude can occur with decreased visual input or poor fixation. VEP results are influenced by attention, alertness, refractive errors, cataracts, and sedation; proper patient cooperation is important.

Clinical uses include assessment of optic nerve and visual pathway integrity in optic neuritis, multiple sclerosis, and other optic neuropathies; monitoring treatment effects; and pediatric evaluation of visual development. Techniques such as multifocal VEP (mfVEP) provide topographic maps of visual field function, offering more detailed spatial information. VEP remains a valuable adjunct in ophthalmology and neurology for objective functional assessment of vision.