Photopic Negative Response Obtained Using a Handheld Electroretinography (ERG) Device: Repeatability and Comparison with Optical Coherence Tomography in Glaucoma

Abstract

Purpose : To determine the repeatability of the photopic negative response (PhNR) measured using a newly commercially available, handheld full-field ERG device that utilizes self-adhering skin electrodes, and compare its magnitude of standardized deficit with neuroretinal parameters on spectral-domain optical coherence tomography (SD-OCT) in eyes with established or suspected glaucoma.

Methods : Sixty-eight eyes from 40 participants with established or suspected glaucoma (considered the glaucoma group) and 47 eyes from 25 normal participants were examined. The PhNR was measured from a combined waveform derived from two measurements with 200 sweeps each, and expressed as a ratio of the B-wave (PhNR/B ratio); each measurement took approximately 60 seconds to obtain. Repeatability of this parameter was also calculated as a percentage of its effective dynamic range (EDR). Retinal nerve fiber layer (RNFL) thickness and Bruch’s membrane opening minimum rim width (BMO-MRW) measurements were obtained from SD-OCT scans. ERG and OCT parameters for the glaucoma group were converted into Z-scores to provide a standardized measure of deficit.

Results : Comparing the two measurements obtained in each eye, the coefficient of repeatability (CoR) of the PhNR/B ratio was 30 ± 4% and 20 ± 2% of the EDR for the normal and glaucoma group respectively (P < 0.001). There was a significant correlation between the Z-scores of the PhNR/B ratio with RNFL thickness (R = 0.595, P < 0.001) and BMO-MRW (R = 0.305, P < 0.001). The average Z-scores for eyes in the glaucoma group were -1.79 ± 0.19, -2.27 ± 0.17 and -3.61 ± 0.44 for the PhNR/B ratio, BMO-MRW and RNFL thickness respectively, being significantly different with all pairwise comparisons (P ≤ 0.020).

Conclusions : Neuroretinal parameters on SD-OCT were significantly correlated with the PhNR of the full-field ERG, but obtained a greater magnitude of measured deficit when examining eyes with established or suspected glaucoma at cross-section. However, the ability to obtain PhNR measurements with such ease using this novel handheld ERG system and with such degree of repeatability using the protocol in this study may provide a valuable tool for objectively measuring short-term or longitudinal changes in neuroretinal function in eyes with glaucoma.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.