Test: Visual Evoked Responses

A visual evoked response test measures the function of the optic nerve, the nerve that transmits messages from the eye to the brain. The test is most often used in the diagnosis of multiple sclerosis and can detect abnormalities even if visual symptoms are not apparent. The test records brain activity in response to a visual stimulus to find out the speed at which messages from the eye reach the brain. The test takes 20–30 minutes.

During the test

Electrodes are attached to your scalp, and one eye is covered. You are asked to focus on a fixed dot of light while the checkered pattern flickers on the screen.

Results

Visual evoked responses

This normal tracing shows electrical activity in an area of the brain as it receives messages from the eye. The first spike on the trace shows the moment of visual stimulus. The time taken for the signal to reach the brain is measured.

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

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