Inter-ocular and inter-session reliability of the electroretinogram photopic negative response (PhNR) in non-human primates

Abstract

Purpose: To assess the inter-ocular and inter-session reliability for a range of parameters derived from the photopic electroretinogram (ERG) in a group of normal non-human primates.

Methods: Inter-ocular differences for photopic ERGs were assessed in a group of normal anesthetized adult rhesus monkeys (Macaca mulatta, n=29); inter-session reliability was assessed for 23 eyes of 23 animals tested 3 months later. Signals were acquired using Burian-Allen contact lens electrodes, whereby the contralateral cornea served as a reference. Photopic ERGs were elicited using red Ganzfeld flashes (-0.5-0.67 log photopic cd.sm(-2)) on a rod suppressing blue-background (30 scotopic cdm(-2)). Measurement reliability was established for a-wave, b-wave, photopic negative response (PhNR) and oscillatory potential (OP) amplitudes, as well as for their implicit times, by calculation of the 95% limits-of-agreement (LOA) and the coefficient-of-variation (COV) for each parameter.

Results: OP and a-wave amplitudes increased with intensity up to 0.67 log photopic cd.sm(-2), following a typical saturating function, whereas b-wave and PhNR amplitudes both declined above 0.42 log photopic cd.sm(-2). Inter-session variability was greater than inter-ocular variability. The inter-session COVs for PhNR amplitude (10-20%) were similar to the other photopic ERG components (a-wave: 12-17%, b-wave: 12-17%, OPs: 13-19%). Inter-session LOAs were also similar across components, but on average, were smallest for responses to moderate intensities (0.0-0.42 log photopic cd.sm(-2)).

Conclusion: In non-human primates, the 95% LOA for inter-session measurements of the photopic ERG a-wave, b-wave, OPs and PhNR are all similar. Inner-retinal damage may best be measured using the PhNR amplitude for moderately bright stimulus intensities. B-wave and PhNR amplitudes for brighter flashes are smaller and more variable. The ratio of PhNR:b-wave amplitudes manifests smaller variability and may therefore be useful for detection of selective PhNR loss.