First Author: T.Soorma UK
Co Author(s): D. Kozareva E. Yonova-Doing I. Hossain M. Stanford C. Hammond O. Mahroo
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We sought to quantify associations between age and photopic electroretinogram (ERG) parameters as recorded using a hand-held device and skin surface electrodes (the RETeval system, LKC Technologies Inc., Gaithersburg, MD, USA) in a large normative adult cohort.
The TwinsUK cohort, based at St Thomas’s Hospital in London, which consists of a large number of largely healthy adult twins who have volunteered to participate in research studies.
Photopic ERGs were elicited and recorded from participants in standard room light conditions. Pupils were not dilated, but the device measured pupil area and adjusted stimulus intensities accordingly, aiming to deliver retinal illuminances equivalent to international standards. Skin electrodes were applied without the skin being cleaned first, to minimise delay. Flash stimuli were delivered, followed by flicker stimuli, with the right eye stimulated first, and then the left. ERG parameters (flash a-wave and b-wave amplitudes and implicit times, and flicker amplitudes and implicit times) were averaged from both eyes where recordings from both eyes were available. As members of a twin pair are correlated with one another, only one twin from each pair was included when exploring correlation with age.
Recordings were made from 679 subjects. Mean (SD) age was 55.8 (14.5) years). Ages ranged from 18 to 84 years (median 59.8 years). Mean (SD) a-wave and b-wave amplitudes were 7.1 (9.3) and 26.6 (12.7) microvolts respectively. Mean (SD) a-wave and b-wave implicit times were 12.4 (3.1) and 29.1 (2.0) ms respectively. Mean (SD) flicker ERG amplitudes and implicit times were 27.6 (9.9) microvolts and 25.9 (1.4) ms respectively. Spearman correlation coefficients with age were as follows for amplitudes and implicit times respectively: -0.33 (p<0.0001) and 0.48 (p<0.0001) for flicker ERG; -0.12 (p=0.027) and 0.13 (p=0.014) for flash a-wave; -0.23 (p<0.0001) and 0.47 (p<0.0001) for the flash b-wave. For the two parameters (flicker and b-wave implicit times) with moderately strong age correlations (>0.45), a linear fit was applied to the data: this gave an average increase of 0.36 ms and 0.54 ms per decade for flicker and b-wave implicit times respectively.
Amplitudes of all components showed statistically significant negative correlations with age, whilst implicit times increased with age, suggesting that cone-driven retinal processing may slow with increasing age. The correlations were weaker for a-wave and b-wave amplitudes and a-wave implicit times, but stronger for b-wave and flicker implicit times. This may relate in part to the lower signal-to-noise ratio for amplitudes when recording with skin electrodes.