Electroretinogram (ERG)
The electroretinogram (ERG) measures the mass electrical activity of the cells within the retina in response to light stimulation. It provides objective information about widespread retinal function of rods and cones, and of the inner retina. It is recorded using a contact lens electrode placed on the cornea after the patient is given topical anesthesia. The patient is presented with a flash of light, and the electrodes record the retinal potentials. The ERG is considered the primary diagnostic test for a variety of retinal dystrophies and degenerations (including retinitis pigmentosa and cone dystrophies), as well as inflammatory, vascular and toxic disorders.