What to Know About the Visual Evoked Potential Test for Multiple Sclerosis

Having multiple sclerosis (MS) comes along with a lot of testing. In part, that’s because MS is an unpredictable disease—and people with the condition don’t necessarily follow a common path of progression or an identical set of symptoms. So, doctors use a variety of tests to not only diagnose the condition, but help track it, so that you can get the treatments you need. One of these tests is the visual evoked potential test (VEP), which can clue doctors in on vision damage that occurs as the result of MS.

A visual evoked potential test is a non-invasive test where electrodes are placed on the scalp to measure the electrical activity of the visual cortex (the part of the brain that processes visual information from the retina). The test uses a visual stimulus—a flashing checkerboard pattern—to assess the function of (and potential damage to) the optic nerve.

“The optic nerve, through which we perceive the world, is a common place where MS attacks,” says Vijayshree Yadav, M.D., the director of the Multiple Sclerosis Center at Oregon Health & Science University in Portland and a professor of neurology at the OHSU School of Medicine. Your optic nerve is located at the back of your eye and connects to the brain; it sends signals to your brain, which puts together the picture you see, explains the American Academy of Ophthalmology (AAO).

MS is an autoimmune disease that can cause inflammation that damages the optic nerve, leading to optic neuritis, a condition marked by eye pain, blurred vision, and loss of color vision, according to the National Multiple Sclerosis Society. In diagnosing and tracking MS, doctors pay close attention to vision changes, as about 70% of patients with MS will experience an episode of optic neuritis sometime during their disease, points out research in Current Issues in Molecular Biology.

Visual Evoked Potential Test Procedure

If you receive a VEP test, you will sit down in front of a screen with electrode leads attached to your scalp. You will then see a flashing checkerboard pop up on a screen. As you watch, “the leads are recording the electrical activity of the activation of the retina and how the signal moves back and forth from the retina to the brain,” says Dr. Yadav. By tracking the way light moves along the visual pathway between your retina and your brain, the test can pick up delays that indicate abnormal functioning of the optic nerve.

While once a mainstay of MS testing, VEP tests are now rarely used for MS, says Scott Grossman, M.D., a neuro-ophthalmologist at NYU Langone Health in New York City. “VEP is an older test. It’s not often used clinically today,” he says.

Dr. Yadav agrees. “VEP was used in the past, but the role of it is not needed much nowadays. It’s mostly used for research purposes, though it may be ordered in practice if a clinician is unsure if symptoms are coming from MS or another cause,” she says.

Why has it fallen out of favor? There are simply better tests available these days that examine the structure of the back of the eye and the thickness of the optic nerve, Dr. Grossman says. One such test is an optical coherence tomography, or OCT. This non-invasive imaging test uses light waves to take pictures of the layers of your retina and measure their thickness, according to the AAO. Researchers writing in the Annals of Clinical and Translational Neurology say that the OCT test is increasingly reliable for monitoring MS disease progression and determining how much neurodegeneration is present, including at early stages of the disease.

The OCT test is used in a variety of settings, and in the context of MS its function is to look at how MS is affecting your visual system. There are many benefits to OCT over VEP: “OCT is easily reproducible, fast, and can be performed even if the patient has a physical or cognitive impairment,” says Dr. Grossman.

Other tests that may be given include a low-contrast letter acuity test. This looks similar to a standard eye chart (where letters are large up top and become gradually smaller), but the contrast of the letter changes compared to the background—dark black letters fade to white with different gradations of gray in between, Dr. Grossman explains. This test has been found to be an effective way to measure vision loss and potential visual impairment and disability, according to a review of research. “It may demonstrate more signs of damage compared to a conventional eye test,” Dr. Grossman says. In addition, a traditional comprehensive eye exam is also important for people who have MS, adds Dr. Yadav.

According to the Cleveland Clinic, VEP tests require a neurologist or neurophysiologist to interpret the waves your brain creates in response to the visual stimulus and how they compare to what is normal and expected. They plot these on a graph, and then take this interpretation and give a report to your health care provider who will discuss the results with you.

The results show how signals move around the optic nerve pathway, an indication of if the optic nerve is functioning normally or not. This can provide information on how much the optic nerve is damaged. However, the reason why the field has moved to tests like OCT is that VEP is very technique-dependent, says Dr. Yadav. Meaning, the person administering the test and the person interpreting the test must be highly skilled; there is also room for error, she says. With better, more reliable options that have less of a risk for user error, the field is shifting away from VEP.

There are a few types of evoked potential tests, including the somatosensory evoked potential test (SEP), which may be used for multiple sclerosis. This test uses electrical stimulation to measure nerve impulses from peripheral nerves to your spinal cord and to your brain, according to Cleveland Clinic. However, magnetic resonance imaging (MRI) is now used to look for lesions or scarring on the spinal cord in MS, says Dr. Yadav.

While evoked potential tests could be a tool in the diagnosis of MS, doctors do not rely on just one test for confirmation of the disease, according to the National Institute of Neurological Disorders and Stroke. To diagnose MS, doctors may use the following exams:

• Medical history

• MRI scans of the brain and spinal cord to look for MS lesions

• Neurological exam

• Physical exam

• Spinal tap (lumbar puncture)

In addition, other tests are more commonly used outside of VEP testing, like the OCT, which can be used as a diagnostic test or during MS treatment. “We can use OCT to be sure that the visual nerve isn’t getting progressively damaged, even in ways patients are not aware of,” says Dr. Grossman.

Visual evoked potential (VEP) tests measure the function of the optic nerve, a nerve that connects the back of your eye to your brain to form pictures of what you see. Inflammation in MS can cause damage to the optic nerve, leading to blurred vision and other problems. However, VEP tests are no longer commonly used, and instead optical coherence tomography (OCT) or other vision tests are now considered standard-of-care, as they’re more reliable and easier to perform.

Because vision changes commonly occur in MS, if you’ve been diagnosed with the disease, get a baseline eye exam, even if you’re not having vision symptoms just yet, recommends Dr. Grossman. Monitoring changes in your eye can help safeguard your sight.