The primary objective of the electophysiologic examination is to assess the function of the visual pathway from the photoreceptors of the retina to the visual cortex of the brain. Information obtained from these diagnostic tests helps establish the correct diagnosis or may rule out related ophthalmic diseases. Electrophysiologic testing is useful in diagnosing a variety of inherited retinal diseases, toxic drug exposure, intraocular foreign bodies, and retinal vascular occlusions. Electrophysiologic testing is performed most often in large referral centers which have expertise in obtaining and interpreting these data. Photoreceptors are nerves in the eye which are sensitive to light.
Cones provide central reading vision, and are responsible for color vision.
There are 6 to 7 million cones in the retina of which about 650,000 are concentrated in the foveola for central vision. Rods provide night vision and detect motion. There are about 120 million rods in the retina of which none are located in the foveola. Minute electrical voltages are produced by the eye. Small electrodes placed about the patient's eye record these micro-voltages as different lighting conditions are presented.