A technique of recording localized electroretinograms (ERGs) with macroelectrodes is described. The localized ERG showed a typical a wave and b wave which confirmed the idea that the ERG can be a response to a focal as well as a nonfocal stimulus. An electroretinographic map of the retina is shown. At the optic nerve head the ERG is absent or is markedly reduced in amplitude. The change in the amplitude of the b wave from the central area to the periphery is not smooth; on the contrary, abrupt changes in the amplitudes were found. An area in the inferior half of the retina was found which gave large amplitude ERGs. This area was seen in all of the retinas plotted although its exact shape and size varied.
DUCO HAMASAKI and ELWIN MARG, "Localized Electroretinograms from the Isolated Retina of the Frog," J. Opt. Soc. Am. 48, 418-421 (1958)