Intraretinal recordings of slow electrical responses to steady illumination in monkey: isolation of receptor responses and the origin of the light peak.

The onset of steady illumination of the mammalian retina initiates a series of complex electrical responses. Corneal recordings in man show a relatively fast ERG, followed by a much slower "light response": a "light peak" followed by a series of damped slow oscillations that may last for 1 or 2 hr. The latter oscillations are a prominent feature of the EOG. We recorded the response to steady illumination with micro electrodes in the intact rhesus monkey eye. The intraretinal "light response" was analyzed by simultaneous recordings at different depths, using a bipolar microelectrode. We found that a steady photoreceptor component can be isolated by fractional recording across the cone outer segment layer in the fovea. Further, through simultaneous recordings at the retinal and choroidal sides of the retinal pigment epithelium, we found that this structure is most probably the generating site of the "light peak" and subsequent oscillations of the standing potential.