Electroretinograms will be recorded using DTL fiber electrodes moistened with carboxymethyl-cellulose sodium 1% lying in the inferior fornix of each eye. Each DTL fiber will be laid along the top of the lower eyelids so that it contacts the inferior cornea. Fibers will be anchored with small adhesive pads near the inner and outer canthi. A reference electrode will be applied with adhesive paste lateral to the outer canthi. An adhesive electrode placed on the forehead will serve as the ground. Prior to pupil dilation, PERG responses will be recorded, including P50 (derived from macular photoreceptors) and N95 (post-photoreceptor, including optic nerve), in response to an alternating checkerboard pattern. Pupils will then be dilated with tropicamide 1% and phenylephrine hydrochloride 2.5% for the full-field ERG and PhNR recordings. The patient will be dark-adapted for 30 minutes. For full-field recordings, stimuli will be brief white flashes presented by a Ganzfeld integrating sphere. Responses to dim and bright flashes will be recorded under scotopic conditions, and a- and b-wave amplitudes will be noted. Patients will then be light adapted for ten minutes. Responses to bright flash and 30 Hz flicker responses will then be recorded under photopic conditions. A- and b-wave amplitudes and implicit times will be noted. Finally, the photopic negative response (PhNR) will be recorded with a red flash on a blue background.