Area under the response waveform following the b-wave peak and its relationship to oscillatory potential amplitude

Abstract

Purpose : To explore how the photopic negative response (PhNR), measured as the area under the response waveform, is correlated to the oscillatory potentials (OP) amplitude and the amplitude of other major ERG components.

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. For OP extraction, the signal was filtered using high-pass 8^th order Butterworth filter with 58Hz cut-off frequency. The root mean square (RMS) of the filtered signal was calculated to define the OP amplitude. The OP RMS values were compared by linear regression to the area under the curve (AUC) of the waveform response in 4 fixed time windows (5, 10, 15 and 20 ms starting at the b-wave peak) and one variable time window starting at the b-wave peak and ending at the trough between the b-wave and i-wave, referred to as PhNR1. As an additional analysis, we compared the AUC in different time windows to a- and b-wave amplitudes and to PhNR1 amplitude.

Results : ERG recordings of 70 patients/135 eyes (52F/18M, average age: 49.2 ± 15.3 years) were evaluated. The AUCs were ranked by R² values and the ranking order was as follows: 10ms AUC and 15ms AUC (range 0.9257-0.9291; 0.9208-0.9339, respectively), 20ms AUC (0.8515-0.8703), 5 ms AUC (0.8187-0.8205) and PhNR1 AUC (0.6833-0.7027). When AUC were compared to b-wave amplitudes instead of OP, the R² values were generally smaller, although the ranking was similar: 15 ms (0.90-0.92), 20 ms (0.88-0.89), 10 ms (0.84-0.86), PhNR1 (0.73-0.79) and 5 ms (0.71-0.72). The R² values were even lower with a-wave amplitude showing similar ranking: 15 ms (0.75-0.79), 20 ms (0.76-0.77), 10 ms (0.73-0.75) PhNR1 (0.63-0.64) and 5 ms (0.63-0.63). PhNR1 amplitude vs AUC R² values were even higher than either a- or b-wave amplitude (range 0.77-0.97) showing similar ranking pattern.

Conclusions : Overall, our results demonstrate that the AUC restricted to 15 or 20 ms time windows is better correlated to the OP or PhNR1 AUC vs. traditionally measured major ERG components like a- and b-wave. This could allow using this parameter as a measure of inner retinal function in clinical settings.

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