Your brain and spinal cord make up your central nervous system, and they both contain neurons. Parts of these neurons are protected by an insulating layer called a myelin sheath.
MS is a chronic condition. Experts aren’t sure what causes it, but some risk factors have been identified.
If you or a doctor suspect you have MS, there are a number of tests that might be performed to help confirm a diagnosis. While no one test can be used to definitively diagnose MS, the following tests can be used to rule out other conditions with similar symptoms:
Another test that’s sometimes used to diagnose and monitor MS is a visual evoked potential (VEP) test. This article takes a closer look at the VEP test, including how it’s used for MS, what the procedure is like, and what you can learn from the results.
A VEP is the brain’s electrical response to visual stimuli. A VEP test measures the electrical activity in your brain.
When light waves enter your eye, they’re absorbed by specialized cells called cones and rods. These are located in your retina in the back of your eye. Your retina turns these light waves into electrical signals that then travel down your optic nerve to the back of your brain, and your brain interprets this as visual information.
During a VEP test, you’ll be shown high-contrast patterns that flash and alternate. While this happens, you’ll have electrodes attached to your scalp.
Using the electrodes, a computer measures the timing of the flashing patterns as well as the timing of the electrical activity in your brain. Doctors or healthcare professionals can use these measurements to figure out how long it takes for the flashing lights to turn into electrical impulses in your retinas and then travel down your optic nerves.
If you have MS, your immune system attacks the myelin sheath that insulates your neurons. This is called demyelination.
Demyelination makes it more difficult for electrical signals to travel across your neurons. This includes your optic nerves, which stretch from the back of your eyes to pathways that reach the back of your brain.
If the myelin along your optic nerves is damaged, a VEP test will find the delay — called latency — between when you’re shown a pattern and when the signal reaches the back of your brain.
A VEP test is one tool that a doctor might use to diagnose MS. A significant delay could be an indicator of MS. For some people, the delay is measurable by a VEP test but small enough that you might not have noticed the effects yet.
VEP tests can also be used to measure the progression of demyelination.
A VEP test is a simple and painless procedure. You won’t need to make any special preparations such as fasting or ingesting special dyes.
The test will be performed in a medical setting such as an examination room at a doctor’s office or hospital.
Several wires will be attached with an adhesive to your scalp, especially in the occipital region, which is at the back of your head.
Then you’ll be seated in front of a computer monitor. The monitor will display a high-contrast pattern such as a checkerboard or alternating bars. This pattern will regularly flicker, with the dark parts changing to light and vice versa.
Each eye is typically tested individually. You can expect the whole procedure to last between 30 and 60 minutes. Most people go home the same day. If you’re able to drive yourself to the test, you can expect to drive yourself home as well.
A VEP test produces immediate results in the form of a graph. It looks similar to the measurements from a heart rate monitor, with peaks and troughs representing electrical activity.
Depending on where the test is taken and who administered it, a doctor may be able to review the results with you right away. In other cases, a technician might need to send the results to a specialist, such as a neurologist, to review before sharing with you.
While VEP tests can find diminished or delayed electrical activity in your brain, they can’t necessarily determine the cause. For this reason, other tests may be needed before you can get a diagnosis.
Can a VEP test confirm a diagnosis of MS or are other tests needed?
Any condition that affects the optic nerves or disrupts the visual pathways to the visual cortex in the brain can affect the brain’s VEP. You may need additional tests to rule out other conditions.
What other types of evoked potential tests do doctors use for MS?
Sometimes doctors may want to run other evoked potential tests such as:
The VEP test is used most often for MS.
Are VEP tests used to diagnose and determine other health conditions?
Yes, there are several uses for VEP tests. Some examples include monitoring gliomas and hydrocephalus. VEP tests can also be useful in certain circumstances during surgery or for people who are in a coma.
A VEP test showing a normal range of activity can usually rule out any abnormality of the optic nerves.
VEP tests are a quick, cost-effective, and noninvasive way to measure your brain’s ability to interpret visual information. Electrodes on your scalp measure the electrical activity in your brain while you watch alternating patterns on a monitor.
The results of the test can tell you whether your brain is responding normally to visual information, but it can’t necessarily tell you the underlying cause.
VEP tests can be used to help diagnose and monitor the effects of MS, though they’re also used in conjunction with other methods. And while they’re helpful tools for people with MS, they can also be used for a number of other conditions.