Electroretinography
Medical Author: John Sheppard, MD
Medical Editor: Melissa Conrad Stöppler, MD
What is electroretinography?
Electroretinography (ERG) is an eye test used to detect abnormal function of the retina (the light-detecting portion of the eye). Specifically, in this test, the light-sensitive cells of the eye, the rods and cones, and their connecting ganglion cells in the retina are examined. During the test, an electrode is placed on the cornea (at the front of the eye) to measure the electrical responses to light of the cells that sense light in the retina at the back of the eye. These cells are called the rods and cones.
How is an ERG done?
The patient assumes a comfortable position (lying down or sitting up). Usually the patient's eyes are dilated beforehand with standard dilating eye drops. Anesthetic drops are then placed in the eyes, causing them to become numb. The eyelids are then propped open with a speculum, and an electrode is gently placed on each eye with a device very similar to a contact lens. An additional electrode is placed on the skin to provide a ground for the very faint electrical signals produced by the retina.
During an ERG recording session, the patient watches a standardized light stimulus, and the resulting signal is interpreted in terms of its amplitude (voltage) and time course. This test can even be performed in cooperative children, as well as sedated or anesthetized infants. The visual stimuli include flashes, called a flash ERG, and reversing checkerboard patterns, known as a pattern ERG.
What do the electrodes do?
The electrodes measure the electrical activity of the retina in
response to light. The information that comes from each electrode is
transmitted to a monitor where it is displayed as two types of waves,
labeled the A waves and B waves.
How are eletroretinography readings made?
Readings during eletroretinography are usually taken first in
normal room light. The lights are then dimmed for 20 minutes, and
readings are again taken while a white light is shined into the eyes.
The final readings are taken as a bright flash is directed toward the
eyes.
Why is an ERG done?
An ERG is useful in evaluating both inherited (hereditary) and
acquired disorders of the retina. An ERG can also be useful in
determining if retinal surgery or other types of ocular surgery such as cataract extraction might be useful.
Next: What diseases is my doctor looking for with an ERG? »
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