Distinct electroretinographic oscillatory potential generators as revealed by field distribution

Oscillatory potentials (OPs) of the electroretinographic signal were recorded in five healthy subjects by means of dermal electrodes located at various positions along the infraorbital ridge and referred to either a frontal or a temporal electrode. Flashes of light were generated in a Ganzfeld stimulator, and OPs were recorded with the subjects' eyes in abduction and adduction. This arrangement of eyeball and electrode positions makes it possible to record the retinal activity from various axes; from a pupillary-posterior pole (longitudinal) axis to an equatorial axis. The individual OPs were found to be selectively affected by the axis of recording, thus suggesting distinct sources of generation. All the OPs reversed in polarity as the recording axis maintained by the electrodes was moved from the longitudinal to the transverse axis. The point of inversion of OP2 and OP3 was similar, as was their amplitude ratio (OP3/OP2), which remained independent of the eye position. However, OP4 became inverted at a different location, closer to the longitudinal axis, and the amplitude ratio (OP4/OP2) varied significantly with the eye position. Altogether, these results suggest different retinal source generators for OP2 and OP3, and for OP4.