The luminance-response function of the photopic negative response (PhNR): analysing different stimulation, recording...

The photopic negative response (PhNR) is a measure of generalised retinal ganglion cell function. There has been heterogenous methodology to record this, with varied electrode type, stimulus luminance, temporal frequency and measurement approach. This study aimed to empirically explore these features to identify an optimal PhNR luminance-response protocol which produces the lowest variance and maximal efficiency to guide clinical protocols.

Twelve healthy participants were recruited (age range 27-51y). Flash ERGs were simultaneously recorded from infraorbital skin and corneal fibre electrodes to a range of red flash stimuli (- 0.3-2.4 log cd.s/m², incremented in 0.3 log units), whilst varying temporal frequency (1-5 Hz), background blue luminance (1, 1.5, 2 log cd/m²), and PhNR measurement approach (from baseline or b-wave, as an amplitude or ratio). The luminance-response series data were analysed for changes according to these variables, alongside a calculation of variability.

The PhNR luminance-response curves showed few significant differences with increasing temporal frequency, though inter-subject variability was highest for the slowest (1 Hz) and highest flash (5 Hz) stimulation rates. Background luminance reduced the relative sensitivity (K) but not maximal amplitude of the luminance-response curves (V_max). With skin electrodes the b-PhNR amplitude and b-PhNR ratio showed the lowest levels of variability compared with other measurement approaches or electrodes.

This study demonstrates that temporal frequency can be increased significantly, optimally at 4 Hz, without compromising the PhNR. PhNR variance is lower with skin electrode recordings and PhNR amplitude measurements from the b-wave compared to corneal fibre electrodes and baseline-PhNR amplitudes.