The electrophysiological findings in optic nerve and primary ganglion cell dysfunction are reviewed. The value of the pattern reversal visual-evoked potential (VEP) in the diagnosis of optic nerve disease, and the pattern appearance VEP in the demonstration of the intracranial misrouting associated with albinism, are discussed. The pattern electroretinogram (PERG) is used in the direct assessment of ganglion cell function. The use of PERG or multifocal electroretinography (mfERG), to enable the distinction between VEP delay due to optic nerve disease and that due to macular dysfunction, is described.