Recording Focal Macular Photopic Negative Response (PhNR) from Monkeys

Abstract

To record the photopic negative response (PhNR) of the focal electroretinograms (ERGs) from the macula of monkeys and to study the properties of the focal macular PhNRs. Focal macular ERGs were recorded from five rhesus monkeys using a modified infrared fundus camera, in which a red stimulus spot on a blue illuminated background were incorporated. The effects of different stimulus intensities and durations presented on a steady blue background of 100 scot cd/m(2) on the focal macular PhNRs were investigated. Focal macular PhNRs were also recorded before and after an intravitreous injection of tetrodotoxin (TTX). Focal ERG responses from a photocoagulated retinal site were recordable when the luminance of the red stimulus spot was <or=55 phot cd/m(2) and was presented on a steady blue background of 100 scot cd/m(2). The amplitude of the focal macular PhNR increased with increasing stimulus intensities and was larger than that of the b-wave at all stimulus intensities. The amplitude of the focal macular PhNR was largest at stimulus durations of 30 to 50 ms. An intravitreous injection of TTX essentially eliminated the focal macular PhNR. It is possible to record focal macular PhNRs from monkeys by using a red stimulus spot on a blue background. Investigations of focal PhNRs can be a useful method of studying inner retinal function of local areas in normal and diseased retinas.