A visual evoked potential (VEP) test is a noninvasive test that helps healthcare providers diagnose certain conditions that affect how your eyes and brain work together to interpret what you see. Some examples of these conditions include multiple sclerosis, head or brain trauma and a glioma on your optic nerve.
A visual evoked potential (VEP) test measures the electrical signal your visual cortex (a region of your brain) generates in response to visual stimulation. The test is also called a visual evoked response (VER).
More specifically, a VEP test assesses the function of your visual pathway, which includes your:
Any abnormality that affects the visual pathways or visual cortex in your brain can appear as an abnormality on the VEP test.
Visual evoked potential tests can help diagnose or point to the following conditions:
VEPs can also help providers assess the progression of certain already-diagnosed neurodegenerative conditions. Examples of these conditions include:
A visual evoked potential test involves electrodes placed on specific parts of your scalp and viewing a visual stimulus — most commonly, a flashing checkerboard pattern.
Electrodes on your scalp measure electrical signals (impulses) as they travel between brain cells. As the visual pattern flashes, your visual pathway responds to and interprets the stimulus. The electrodes record the electrical activity in your brain that results. Healthcare providers run VEP tests in the background of an electroencephalogram (EEG).
The evoked potential machine averages the EEG signals following multiple visual stimuli so it can assess the functioning of your visual pathway. The evoked potential machine records the electrical response to visual stimulation on several channels or traces. Your brain (visual cortex) has specific waveforms that occur at very specific times in response to a visual stimulus.
A specialist then interprets the wave patterns and looks for abnormal activity, which can point to various issues with your visual pathway.
Your healthcare provider will go over what to expect during the test and what to do prior to it. Don’t hesitate to ask questions or voice your concerns. Be sure to follow their preparation instructions.
Before the test, you’ll need to make sure your hair is clean and doesn’t have any hair sprays, oils or gels in it. These products can interfere with the function of the electrodes.
There are several different types of VEP tests, so the process may vary.
You can generally expect the following:
The test may take up to 60 minutes to complete.
Once a specialist has interpreted the results of your VEP, they’ll put together a report and send it to your healthcare provider. Your provider will then share the results with you.
VEPs can detect several different issues in your visual pathway. And each issue has a different presentation in terms of the shape of the wave and the length of time between the stimulus and your brain’s activity. For example, in demyelinating conditions of the optic nerve (like MS), the VEP test shows a delay in your brain’s responses.
Again, your healthcare provider will explain the results to you and let you know if you need any additional testing.
A note from Cleveland Clinic
A visual evoked potential (VEP) test is a noninvasive way to help diagnose certain conditions that affect how your eyes and brain interpret visual stimuli. Your healthcare provider will walk you through the process before and after the test. Don’t be afraid to ask questions — your healthcare team is available to help you.
Last reviewed by a Cleveland Clinic medical professional on 01/25/2023.
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