Electroretinography with the RM Electrode: Normal Values, Variation with Age and Comparison with the Burian-Allen Electrode

Abstract

Purpose : The RM Electrode (RETMAP INC) is a new, soft-contact lens based single-use electrode for recording the full-field electroretinogram (ffERG). Aim 1 was to define the normal range with the RM Electrode for ERGs recorded to the International Standard of Clinical Electrophysiology of Vision (ISCEV) protocols. Aim 2 was to compare ERG parameter values from the RM Electrode with the Burian Allen (BA) contact lens electrode.

Methods : ffERGs were recorded from 40 healthy volunteers aged between 21 to 74y (mean ± SD = 39.4 ± 15.7y). Following pupil dilation and 30 min of dark adaptation, ISCEV standard ffERGs were recorded from an RM Electrode placed on the cornea; skin electrodes placed on the outer canthus and forehead served as reference and ground respectively. ffERGs were also recorded for 4 ISCEV extended protocols: DA red flash, photopic negative response to red on blue (PhNR_RB) and blue on yellow (PhNR_BY), photopic On-Off and S-cones. ISCEV ffERGS were simultaneously recorded from a BA electrode in the contralateral eye in a subset of HVs (N=22)

Results : Scotopic ERG amplitudes as well as PhNR and S-cone ERG amplitudes followed a log-normal distribution. Photopic amplitudes recorded to achromatic light and all implicit times were normally distributed. Tables 1 and 2 summarize the normal ranges for amplitudes and implicit times respectively. Log values are converted to linear equivalents. Some scotopic amplitudes (Table 1: DA01, DA3/10 a-wave, OPs & On-Off d-wave) and most implicit times (Table 2) varied with age. Therefore, the mean ± SD, and the lower limit of normal, are shown for a nominal age of 20y. The last columns in Tables 1 and 2 show the decrease in amplitude and increase in implicit time per decade respectively, for those parameters that varied with age. DA3 and LA3 amplitudes were 18% and 20% larger from the RM Electrode compared with the BA electrode; there were no differences in implicit times. However, when the BA electrode was used in a monopolar configuration (ie. equivalent to the RM Electrode) there were no differences in amplitudes between the two electrodes.

Conclusions : We defined the normal range from the RM Electrode for the standard ISCEV ERG protocol and four extended ISCEV protocols. ERG amplitudes and implicit times were equivalent from RM and BA electrodes when used in a monopolar configuration.

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

 

Table 1: Amplitudes

 

Table 2: Implicit times