What Are Visually Evoked Potentials?

Visually evoked potentials (VEP) are electrical signals that occur in the brain when visual stimuli, such as a pattern on a screen or flashing lights, are seen. Testing for this response can be used to pinpoint issues with the nerves of the eye.

With a visually evoked potential test, the idea is to determine just how the visual system is functioning and if there are any optic nerve problems. This commonly used test evaluates the time it takes for your nervous system to respond to things in your line of sight.

The test relies on electrodes placed on the scalp to detect electric current produced by the brain. If the nerve pathway is damaged, even small delays of mere milliseconds can be picked up.

This article will discuss why a healthcare provider may recommend testing visually evoked potentials, the different types, how to prepare for the test, and what to expect.

A close-up of a man's eye reflecting a circle of lights in his pupil.
Milan Tarlac / EyeEm / Getty Images

Purpose

Testing for visually evoked potentials can enable practitioners to detect any damage to the nerves associated with your eyes. This test may be recommended to:

  • Determine if there are any issues in this system, particularly for infants and children who cannot understand eye charts.
  • Map out surgery for eyes with poor vision.
  • Ensure that an illness is physical and not psychosomatic (does not stem from a physical condition).
  • Look for optic nerve damage (neuropathy) or into cases of optic neuritis (inflammation of the optic nerve), which can be associated with multiple sclerosis as well as other causes.
  • Detect optic nerve tumors that may be affecting some of the fibers in the nerve pathway.

How to Prepare

This is considered to be a safe test that's done while you are fully awake. To prepare for a visually evoked potential test, here's what to keep in mind:

  • Fatigue can be a factor here, so make sure to get plenty of rest.
  • Since sensors will be placed on your scalp, wash your hair before coming, but avoid using any conditioner, hair gel products, oils, or sprays. Also, don't use hair clips that are difficult to remove or put your hair in braids, which may get in the way of the electrodes.
  • Since you will not be needing any sedation, you are free to eat as you normally would prior to the procedure.
  • Be sure to bring your insurance card and any paperwork that your healthcare provider asks you to fill out ahead of time.
  • If you wear glasses or contact lenses, be sure to wear these since you will need your optimal vision for this test.
  • Tell your healthcare provider about any eye conditions you may have, such as cataracts (clouding of the lens of the eye) and any over-the-counter medications or prescriptions you are taking.

What to Expect

When you come in for the test, conducting gel will be applied to your scalp and electrodes placed in the rear area over the occipital region of the brain, which recognizes visual input. This will likely only cause minimal discomfort. Then you will likely be seated in front of a computer screen ready to start the visually evoked potential exam.

Types of VEP Tests

Visually evoked potential testing is usually done in two parts, using what's known as a pattern VEP, followed by a flash VEP. Each eye will likely be tested. Your only job will be to stay focused while watching the screen. The two parts take about one hour altogether. Here's how these two tests work.

Pattern VEP

With a pattern VEP test, you'll be asked to look at a computer screen where you'll be shown something that looks much like a checkerboard. During the test, the squares will change in size, move around the screen, and reverse color once or twice a second.

Throughout, electrodes placed on top of your head will register changes in electrical signals from your brain. This part of the test tends to be more time-intensive than the second part of the exam.

Flash VEP

For the second part of the exam, a special machine containing a light inside is used. You will be asked to closely watch the light as it flashes, with the electrodes registering what's going on as this occurs.

After the Test

Once the test is complete, a neurologist (physician specializing in nervous system conditions) will look over the results. They will be able to determine whether any symptoms you are having are related to nerve issues. The neurologist will then send the results to your healthcare provider.

Your healthcare provider will then discuss the results with you and develop a plan of action if one is needed.

Summary

A visually evoked potential test can help to detect vision issues for children and others who are unable to fully participate in an eye exam. It can also detect even slight nerve damage to the optical system that may be associated with a condition such as multiple sclerosis.

It is a relatively painless test that takes no more than one hour. During this time, it only requires you to remain focused throughout.

A Word From Verywell

If you've been asked to undergo a visually evoked potential test, go in knowing this is an effective exam that can help to find even early issues that may be affecting your optical nerves. With the aid of this test, it may then be possible to identify an issue affecting the nerves and take steps to preserve nerve function as early as possible.

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5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Multiple Sclerosis Trust. Evoked potentials.

  2. Johns Hopkins Medicine. Sensory evoked potential studies.

  3. American Clinical Neurophysiology Society. Visual evoked potentials.

  4. University of Michigan Health. Visual evoked potential (VEP).

  5. University of Pittsburgh Medical Center. Visual evoked potentials (VEP) testing.