The cortical visual evoked potential (VEP) provides information about the health and function of the visual pathways from the optic nerve as it leaves the back of the eye, to the visual center in the brain. Many people require a combination of these tests to give the complete information about their visual problem.

The visual evoked potential (VEP), or visual evoked response (VER), is a measurement of the electrical signal recorded at the scalp over the occipital c ortex in response to light stimulus. The light-evoked signal, small in amplitude and hidden within the normal electroencephalographic (EEG) signal, is amplified by repetitive stimulation and time-locked, signal-averaging techniques, separating it from the background EEG readings. The precise origin of the VEP signal remains unclear, but it reveals the integrity of the afferent visual pathway; damage anywhere along the path may reduce the signal. The VEP is primarily a function of central visual function, because such a large region of occipital cortex is devoted to macular projections. Thus, peripheral visual loss might be overlooked by VEP testing.

Ophthalmic Electro-Diagnostic Test

Test NameArea TestedTime TakenDilating Drops
Flash ERGGlobal Retina(rods and cones)60 minutesYes
Pattern ERGMacular (central retinal) function30 minutesNo
EOGRetinal Pigment epithelium30 minutesNo
Cortical VEPVisual pathway (optic nerve to visual center in brain45 minutesNo

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