Electroretinography (ERG) provides information as to overall retinal function and a more specialized ERG (foveal ERG) is of value in assessing the macula. It is particularly important in degenerative conditions of the retina (retinitis pigmentosa, juvenile macular degeneration, toxic retinopathies associated with drugs such as Plaquenil, Chloroquine, Mellaril and related compounds, and others. A related test, electro-oculogram (OCG) is performed to in cases of another specific, macular degeneration, Best’s Disease. ERGs and EOGs, though of great usefulness in diagnosis and extremely important for prognosis, are not widely available and for proper testing and interpretation, patients must be referred. The best center is the ERG Service at the Massachusetts Eye and Ear Infirmary.