mfVEP

Multifocal visual evoked potential (mfVEP) is a diagnostic electrophysiological test that assesses the functional status of the visual pathways by recording electrical activity from the occipital cortex in response to locally targeted visual stimuli presented across the visual field. Unlike conventional VEP, mfVEP simultaneously records responses from many peripheral and central field locations, allowing a topographic map of function to be derived. The stimuli are typically a dartboard-like array of checkerboard patches whose contrasts are reversed in a pseudorandom sequence (often based on m-sequences). The cortical responses are extracted by cross-correlating the EEG with the stimulus sequence, producing a separate waveform and amplitude/latency estimate for each field location.

The test is performed with scalp electrodes (commonly Oz as active, with Fz/Cz as reference and a ground electrode) while the patient fixates on the center. Refractive errors and media clarity are corrected to optimize signal, and adequate electrode contact is essential. Results are displayed as topographic maps of amplitude or latency, highlighting regions with reduced function or delayed conduction, corresponding to visual field deficits or optic pathway damage.

mfVEP is used as an objective complement to psychophysical tests in conditions such as optic neuritis, multiple sclerosis, glaucoma, and other optic neuropathies, particularly when standard perimetry is unreliable or when cortical localization of deficits is clinically informative. Limitations include sensitivity to fixation instability, poor signal quality, and the need for specialized equipment and normative databases.