Original versus filtered response in standard light adapted 3.0 ERG: differences in photopic negative response recordability

Abstract

Purpose : The standard light adapted 3.0 (LA3) full-field ERG signal represents a combination of ERG components containing low frequencies (< 60 Hz; a-wave, b-wave, i-wave, and photopic negative response (PhNR)) and those containing high frequencies (> 60 Hz; oscillatory potentials (OPs)). Currently the preferred practice is to measure the PhNR from ERG signals containing all frequencies. The purpose of this study was to evaluate the effect of PhNR measurements and recordability from a filtered signal.

Methods : A retrospective chart review and data analysis of patients aged 18 and over 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 DTL electrodes. For OP extraction, the signal was filtered using a high-pass 8^th order Butterworth filter with a 58Hz cutoff of the digital filter. The PhNR measurement was done from the peak of the b-wave to the minimum before (PhNR1) or after the i-wave (PhNR2) (Doc Ophthalmol 2020 140: 115-128). For the purpose of this study, the PhNR amplitudes measured in the ‘traditional’ way on the unfiltered signal (PhNR1-t, PhNR2-t) whereas the ones measured in the second way were referred to as ‘filtered’ (PhNR1-f, PhNR2-f). PhNR was considered recordable when a well-defined trough was present to indicate the maximum response.

Results : The records of 70 patients/135 eyes (18M, 52F); mean age 49.2 ± 15.3 years were evaluated. The amplitude of PhNR1-f was 18-20% smaller compared to PhNR1-t for both right and left eyes (60 ± 21.6 vs 74.8 ± 28.1 µV right eyes, 62.8 ± 29.2 vs 76.4 µV ± 34.7 left eyes); however, the recordability of the PhNR1-f was slightly higher (63 vs 61 right eyes, 60 vs 59 left eyes). Similar effects were observed for PhNR2-f, with 20% decrease in amplitude for right eyes and 10% decrease in amplitude for left eyes. However, the effect of PhNR2 recordability was stronger with 38 eyes versus 30 eyes for right eyes (27% increase) and 30 eyes versus 25 eyes for left eyes (20% increase).

Conclusions : An increase in recordability for PhNR was observed if the filtered ERG trace was used instead of the combined one. This may be helpful in future use of PhNR1 in clinical settings.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.