An alternative way to evaluate the photopic negative response amplitude by estimating the area under the response waveform

Abstract

Purpose : To examine the area under the response waveform of the photopic negative response (PhNR) as an alternative way to estimate the magnitude of the response.

Methods : A retrospective chart review and data analysis of patients aged 18 and older undergoing routine ERG testing at USF Eye Institute (Tampa, FL) was conducted. LA3 was recorded using a ~2.5 cd.s/m² white flash on a 30 cd/m² white background with fiber electrodes. The area under the curve (AUC) of the waveform response in 4 fixed time windows (5ms, 10ms, 15ms, and 20ms starting at the peak of the b-wave) and a 5^th variable time window staring at the b-wave peak and ending at trough between b-wave and i-wave, referred to as PhNR1 were compared with linear regression models to the amplitude of traditionally measured PhNR (after the i-wave peak), referred to as PhNR2.

Results : ERG recordings of 70 patients/135 eyes (52F/18M, average age: 49.2 ± 15.3 years) were evaluated. The PhNR2 component was identified in an unambiguous way as a distinct trough after the i-wave peak in 50 eyes (right/left = 26/24), or in 37%. In comparison, the PhNR1 was identified as a distinct trough before the i-weave peak in 94 eyes (right/left = 44/50), or in 72.3%. the amplitudes of PhNR1 and PhNR2 when recorded form b-wave peak (fP) were highly correlated (R² right/left = 0.9747/0.9763). When PhNR2 (fP) amplitude was correlated to AUCs, the ranking of the R² values were as follows (right/left): 15 ms (0.95/0.97), 10 ms (0.92/0.94), 20 ms (0.92/0.85), PhNR1 (0.82/0.88) and 5 ms (0.76/0.80). When traditionally measured PhNR2 amplitude (from baseline, fB) was correlated to AUC, the ranking was similar, but with much lower R² values (0.43-0.49).

Conclusions : These results support previous findings indicating high correlation between PhNR1 and PhNR2 measures and lower recordability for PhNR2 (Ortiz et al. Doc Ophthalmol. 2020, v.140:115–128). It is also demonstrated that the AUC restricted to relatively early time windows (10 or 15 ms) is highly correlated to PhNR2 (fP) amplitude. This could provide an alternative way of determining retinal ganglion cell function, when traditional measures, such as PhNR2 amplitude, are affected by various artifacts.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.