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An Evoked Potential (also known as Evoked Response) is a test to evaluate the condition of certain nerve pathways. The test quickly and safely measures the speed of the signals carried by the nerves.

There are two types of Evoked Potentials: Brainstem Auditory Evoked Potential (BAEP) and a Visual Evoked Potential (VEP). Each test is performed while seated and takes approximately 30 minutes at the Hospital's Neurodiagnostic Laboratory.

Your cooperation is essential. During the procedure, a few electrodes are pasted on to the scalp while a mild "stimulus" (a clicking noise or a flashing checkerboard screen) is applied to the ears or eyes. The stimulus is what causes the nerves to react and send messages to the brain.

Before an Evoked Potential Test

A physician's prescription is required before scheduling an evoked potential test. It is requested that you have clean, dry hair for testing. This allows the electrodes to stay in place and provide a proper recording. You should continue to take your normal medications unless otherwise indicated by your physician. You should also bring your eyeglasses if you are having a VEP. You may be asked to wear them for the test.

During an Evoked Potential Test

A technologist will obtain a history from you, including current medications, and then apply the electrodes. If you are having a brainstem auditory evoked potential (BAEP), you will have earphones placed over your ears to deliver the click stimulus. This process will be repeated several times on each ear. If you are having a visual evoked potential (VEP), an eye patch will be placed over one eye while the other eye is tested by watching a flashing checkerboard screen. Again, the test is repeated several times to ensure accuracy. After the test, the electrodes will be removed and the water soluble paste will be cleaned from your hair. If you have any questions, feel free to ask the technologist.

After an Evoked Potential Test

The test will be interpreted by a neurologist, specially trained in reading evoked potentials. The technologist is not permitted to provide results to the patient during the test. The neurologist will review the results and dictate a report that contains the results of your test. The physician that ordered the test will receive the report and discuss the results with you.


Chester County Hospital
701 East Marshall Street, 2nd Floor
West Chester, PA 19380
Phone: 610.738.2771
Hours: Monday-Friday, 8 am-4:30 pm