Electroretinography is an electrophysiological test of the retina, the layer of the eye which detects light. The Electroretinogram (ERG) is to the retina what the electrocardiogram (ECG) is to the heart. Just as an ECG is crucial to diagnosing illness and monitoring the heart’s function, ERG plays a critical role in the care of the eye and is instrumental in the early detection of retinal dysfunction. Electroretinography provides a wealth of objective, vital information about the retinal function and health and plays a vital role in the diagnosis of acquired and inherited eye diseases and dystrophies. An ERG can also be useful in determining if retinal surgery or other types of ocular surgery such as cataract extraction might be useful. It is the only test that can detect Plaquenil toxicity before significant vision loss has occurred.