What is electroretinography (ERG)?
Electroretinography (ERG) is an eye test measuring the electrical response to light flashes, similar to the way the electrical signals from the heart are recorded with an EKG. It is 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. 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.
How is an ERG done?
The eyes are dilated with standard dilating eye drops. Anesthetic drops are then placed in the eyes, and eyelids are gently propped open with a speculum. A thread-like sensor is placed under the lower eyelid to measure the electrical responses to light. 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, the patient watches a standardized light stimulus of flashes, called a flash ERG, and reversing checkerboard patterns, known as a pattern ERG. Readings are performed after adapting to the dark for 20 minutes, and readings are again taken with white light on. The faint electrical signal is measured for amplitude (voltage) and time course and the patterns analyzed to confirm diagnoses or monitor for safety and health.
What diseases is my doctor looking for with an ERG?
There are a number of conditions, mostly ocular in nature, in which the ERG may provide useful information. The diagnoses most commonly suspected when ordering an ERG are predominantly conditions of the retina, including:
- retinitis pigmentosa,
- retinitis punctata albescens,
- retinitis pigmentosa sine pigmento,
- related hereditary retinal degenerations,
- disorders that mimic retinitis pigmentosa,
- Leber's congenital amaurosis,
- gyrate atrophy of the choroid,
- gyrate atrophy of the retina,
- Goldman-Favre syndrome,
- congenital stationary night blindness,
- X-linked juvenile retinoschisis,
- cone dystrophies, and
- Usher syndrome