What is the VEP test? Why is this test done? (Visual Evoked Potential Test)

Do you sometimes experience slight changes in your vision, blurriness, or pain in your eyes? Maybe your doctor has asked you to have a test called a VEP. It's normal to feel a little scared and curious, "What is this test?" But don't worry, today we'll talk very simply and friendly about what this VEP test is, what it looks for, and how it's done.

Simply put, what is this VEP test?

Think of your eyes as two cameras. What these cameras see, that is, visual information, needs to be sent to the brain. Only when it is sent can we understand exactly what that thing is. So, this VEP (Visual Evoked Potential) test is used to see if this communication path between your eyes and your brain is working properly.

Simply put, this test measures what kind of electrical signal the part of your brain related to vision (visual cortex) emits when you look at a visual stimulus, that is, an image.

All of these parts belong to the communication pathway, or visual pathway, between the eyes and the brain:

• Eyes: Where we see things.
• Optic Nerves: Like cables that carry information from the eyes to the brain.
• Optic Chiasm: A special place in the brain where nerve fibers from the two eyes cross over.
• Optic Tract: The pathway that carries information from the optic nerve to the brain.
• Optic Radiation: Another part of this pathway.
• Cerebral Cortex: The part of the brain that ultimately processes this information and understands, "Here is a chair" or "Here is mom."

If there is a small problem or obstruction anywhere along this entire path, it will show up abnormally in the VEP test.

Why would a doctor recommend a VEP test?

There are several reasons why a VEP test may be ordered. In particular, your doctor may order this test if there is a suspicion of a medical condition that may be affecting your visual field. It can help diagnose a condition or help understand the status of an existing condition.

See the table below for the main medical conditions this test can help diagnose.

How does this test work?

This is actually a very simple, painless procedure. Imagine that you have little sensors attached to your head. In medicine, we call these electrodes .

They attach these little metal disc-like electrodes to your hair at specific locations. Then, you sit in front of a monitor. On that screen, a flashing checkerboard pattern appears and disappears.

When you look at it, your eyes see the image, and that information is sent along the optic nerve to the brain. When the brain receives that signal, electrical activity occurs between brain cells. Electrodes attached to the head measure that electrical activity and record it on a machine. This test is usually done with the help of an EEG (Electroencephalogram) machine that records the electrical waves of the brain.

This machine measures how long it took for the brain to respond to the image from the moment the eye saw it, and how strong that response was. That response is recorded as wave patterns. A specialist analyzes these wave patterns to look for any delays or abnormalities.

How to prepare for the test?

This doesn't require much preparation. However, it is important to follow these steps the day before the test:

• Wash your hair thoroughly and keep it clean. Shampoo, rinse well with water, and dry.
• Do not apply any oil, gel, or hair spray to your hair on the day of the test. If you have these things on your hair, the electrodes will not be able to properly pick up the brain signals.
• Your doctor or hospital will give you further instructions about this. Listen to everything carefully and follow it. Never be afraid to ask if you have any questions.

What happens during the test?

When you go into the examination room, you won't experience anything scary.

1. First, a technician will make you sit comfortably in a chair.

2. Then, the electrodes are attached to specific areas of your scalp with a special type of glue. This glue can be easily removed later.

3. Next, one of your eyes will be covered with a patch.

4. You will be asked to pay close attention to the chessboard pattern that appears on the screen in front of you.

5. Once the test is completed with one eye, the test is repeated in the same way with the other eye.

The entire test can take about 60 minutes . You will not feel any pain during this entire time.

What does the test report say?

The waveforms from the test are analyzed by a neurologist, who measures things like the time it takes for the brain to respond to the signal from the eye (latency) and the strength of that response (amplitude).

For example, in a condition like Multiple Sclerosis (MS), the myelin sheath around the nerves is damaged, slowing down the speed at which signals travel. This can cause the brain to take longer than normal to respond to a VEP test (delayed response). This can give the doctor an important clue about the disease.

The specialist will analyze this and create a complete report, which will be sent to your treating doctor. Your doctor will then explain the report to you. He or she will also tell you if any further tests are needed, or what the next steps should be.