What is the ERG?

ERG stands for "Electroretinogram". The ERG is the massed electrical response of the retina to brief flashes of light. It is used in the diagnosis of retinal diseases. In contrast, the VEP measures the signal that is received by the visual cortex.

ERG contact lens electrode The ERG is recorded using a small contact lens electrode that rests on the front surface of the eye. It doesn't hurt. There's a series of electrodes in different sizes that can be used for very young infants up to adults. The retinal is a collection of rod, cone, and neural cells which make electrical signals which transmit visual information to the brain. By measuring the changes in those signals, it is possible to determine how well the different cells in the retina are working.

In an ERG result, there is are two parts. Initially there is a negative phase called the a-wave, which is the electrical response of the photoreceptor, which is where light gets converted to an electrical signal. The second part is where the graph rises, called the b-wave. This is the response of the post-receptor cells such as the bipolar cells and other neurons. This test make it possible to pinpoint in different diseases the site of the disease's action.

Sample waveform extracted from an electroretinogram (ERG) ERG waveform

Additional Resources for the ERG: