Electroretinogram

In electroretinography A multifocal electroretinogram (ERG) is used to record separate responses for different retinal locations.

Electroretinograms can be broken down into three components:
 * an initial a-wave, caused by extracellular ionic currents generated by photoreceptors during phototransduction,
 * the b-wave, which corresponds to bipolar cell activity,
 * and the later c-wave, which is generated by the retinal pigment epithelium and Müller cells.

Depending on the species the ERG is taken from, the c-wave may be positive, negative, or absent in part or in whole.