Electroretinography (ERG) is an eye test useful in evaluating both inherited (hereditary) and acquired disorders of the retina (the light-detecting portion of the eye).
The multifocal ERG focuses on different areas of the retina, looking for localized areas of abnormality so this test takes longer than a simple ERG.
ERG can be used to diagnose:
- Retinitis pigmentosa
- Retinitis punctata albescens
- Retinitis pigmentosa sine pigmento
- Related hereditary retinal degenerations
- Disorders that mimic retinitis pigmentosa
- Leber's congenital amaurosis
- Congenital stationary night blindness, etc.
It can be performed even in cooperative children, as well as sedated or anesthetized infants.
During an ERG test, the patient assumes a comfortable position (lying down or sitting up) and 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. Then, the eyelids are then propped open with a speculum and the electrodes are 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.
The electrodes measure the electrical activity of the retina in response to light and the information from electrodes are transmitted to a monitor where it is displayed as two types of waves, labeled the A waves and B waves.
A normal ERG shows a normal A- and B-wave pattern with appropriate increases in electrical activity with increased light intensities and an abnormal ERG result suggests abnormal function of the retina due to diseases of the retina or abnormal function of the retina.
The test takes about an hour or less and it is painless, but the electrode that rests on the eye may feel a little like an eyelash has lodged in the eye so patient must rub the eyes. This sensation may persist up to several hours after the test.