Electrophysiology Testing

What is Electroretinography?

Electroretinogram (ERG) and Multifocal ERG (MF-ERG)

Electroretinography (ERG) is an eye test that is used to detect abnormal function of the retina, which is the light-detecting portion of the eye. In this test, the rods, cones and light sensitive cells of the eyes are examined. During the test, an electrode is placed on the cornea (the front of the eye) to measure your retinal cells’ electrical response to light. An ERG is useful in evaluating inherited (hereditary) and acquired disorders of the retina. An ERG can also be useful in determining whether retinal surgery is preferable over other types of ocular surgery. Cataract surgery, for instance, might be useful to improve a patient’s eyesight. Some diseases that the doctor might be testing for include: retinitis pigmentosa, Leber’s congenital amaurosis, choroideremia, Usher’s syndrome, night blindness, cone dystrophies, etc.

The multifocal ERG tests the macular area of the retina, specifically, as opposed to the full field, targeted by a regular ERG. Projected on the screen will be a changing, randomly-sequenced pattern and the electrode will record the electrical activity of the retina.

Visual Evoked Potential (VEP)

Visual evoked potential is a test that records how the visual system records light. During a VEP test, three electrodes are attached to the patient’s head with a type of cement glue. The patient is then asked to stare at a checkerboard pattern on a television screen. Each eye is tested separately. The electrodes record hundreds, sometimes thousands, of electrical responses from the patient’s visual nervous system, and a special computer records these responses. VEP tests are used to evaluate optic neuritis, optic tumors, retinal disorders, and demyelenating diseases such as multiple sclerosis.


Electrooculography (EOG) is a test used for measuring the resting potential of the retina. During an EOG test, you will be asked to focus on a red light in the center of the vision. The red light then moves right to left so forth for 15 seconds out of every minute. Usually, pairs of electrodes are placed to the left and right of the eye. If the eye is moved from the center position towards one electrode, this electrode “sees” the positive side of the retina and the opposite electrode “sees” the negative side of the retina. Consequently, a potential difference occurs between the electrodes. Assuming that the resting potential is constant, the recorded potential is a measure for the eye position. The EOG is used to asses the pigment epithelium of the retina and is useful in diagnosis Best’s disease.