Electroretinography is an ophthalmological test to measure the electrical activity of the cells that make up the retina of the eye; rods, cones, bipolar, amacrine, and ganglion cells. The retina is a sensitive inner layer of the eyeball on which the images we see are focused on. Electroretinography measures the electrical responses of these retinal cells. Electrodes are usually placed on the cornea and the skin near the eye, although it is possible to record the ERG from skin electrodes.
During a recording, the patient's eyes are exposed to standardized stimuli and the resulting signal is displayed showing the time course of the signal's amplitude (voltage). Signals are very small, and typically are measured in microvolts or nanovolts. The electroretinography is composed of electrical potentials contributed by different cell types within the retina, and the stimulus conditions can elicit stronger response from certain components. To do an electroretinography, an ophthalmologist (oculist) uses an electroretinogram (ERG), which is used for the diagnosis of various retinal diseases.