Measuring differences in the ERG in myopia using the RETeval device with skin electrodes.

Introduction: Previous research suggests that the electroretinogram (ERG) is reduced and delayed in non-pathological myopia. However, the invasive nature of the electrode and cumbersome equipment required has prevented the widescale uptake of ERG measures. This study investigated whether previously reported changes to the ERG response in myopia are also observable when measured using non-invasive skin electrodes and a hand-held ERG device.

Method: Monocular flash ERGs were measured using the RETeval® device according to the 'ISCEV 6 Step Dark First cd' protocol in 46 participants with non-pathological myopia (spherical equivalent refraction [SER] -0.50 to -11.25 D, median -3.75 D, median axial length [AL] 25.4 mm) and 47 non-myopic controls (SER +2.00 to -0.25 D, median +1.00 D, median AL 23.6 mm). Measures were performed under pupil mydriasis with Sensor Strip skin electrodes.

Results: The median implicit time for all dark-adapted (DA) components was longer among myopes. Following Holm-Bonferroni correction, this difference reached statistical significance (p < 0.05) for the DA 3.0 A-wave, DA 10.0 A-wave and B-waves, and DA Oscillatory potentials 1 and 2. There were no significant differences between median light-adapted (LA) implicit times nor response amplitudes between refractive groups. For all DA components, there was a significant, positive correlation between AL and implicit time (all p < 0.05).

Conclusions: The RETeval®, used with skin electrodes, did not detect the reduction in ERG amplitude reported in myopic eyes using traditional ERG setups, potentially due to high inter-subject variability and/or anatomical confounders associated with the use of a skin electrode. The RETeval® with skin electrodes did detect subtle delays to DA implicit times previously reported in myopia, with a positive relationship observed between AL and implicit time for all DA components. In contrast, no significant differences were observed for LA implicit times, which may indicate underlying differences in the dark-adaptation process and/or scotopic visual pathways in myopia.