Visual Evoked Potential (VEP)

Visual evoked potentials (VEP) measure the electrical signals generated by your brain in response to visual stimulation. It can detect slowing in the visual pathway even when vision seems normal.

Why It's Done

• Detect subclinical optic neuritis (no symptoms)
• Support diagnosis of multiple sclerosis
• Evaluate unexplained vision loss
• Confirm functional vision loss vs organic
• Monitor optic nerve function over time

What It Measures

• Time for visual signal to reach brain (latency)
• Strength of brain's response (amplitude)
• Delayed latency suggests optic nerve problem
• Response persists even after optic neuritis improves

What to Expect

Before the Test

• Wash hair (no oils or products)
• Bring corrective lenses if needed
• No special preparation

During the Test

• Electrodes placed on scalp (with gel)
• Sit in front of screen
• Watch checkerboard pattern that reverses
• Each eye tested separately
• Takes 30-60 minutes

After the Test

• Wash gel out of hair
• Resume normal activities
• Results interpreted by specialist

Interpreting Results

Normal

• Response occurs within expected time
• Good amplitude

Abnormal

• Delayed response—suggests demyelination (myelin damage)
• Reduced amplitude—suggests axonal damage
• May be abnormal even with recovered vision

When VEP Stays Abnormal

After optic neuritis, VEP may remain delayed even after vision returns to normal. This is useful for:

• Confirming prior optic nerve inflammation
• Supporting MS diagnosis