Occasionally a person experiences visual changes that are difficult to completely understand with only a clinical eye exam. These changes may be due to abnormalities in the function of some of the cells on the back of the eye in the retina, or there may be changes in the nerve connections between the eye and the brain. Electrophysiological tests are types of tests that record responses from nerve cells in the back of the eye and can help your eye doctor better understand what is occurring in the eye.
For these types of tests, a contact lens with an electrode within it is placed on the eye. The patient then watches a screen with different lights to stimulate the retina. The electrical impulses from the retina are recorded. To get useful readings, the patient must first sit in the dark for a period of time to become completely dark-adapted. For this reason, this test usually takes about two hours.