ERG Electroretinography is a specialized test that measures the electrical responses of the various types of cells in the retina layer of the inner surface of the eye. ERG measures electrical signals produced by the light collecting cells in the retina. These cells in your eye called photoreceptors are stimulated by special light patterns like strobes or checkerboards. The response by your cells is recorded by an electrode in contact with your skin. The test is painless and requires no special dyes or radiation. This test is useful to diagnose and follow the progress of retinal diseases including diabetic retinopathy, retinitis pigmentosa, and artherosclerosis (blood vessel disease).