Proceedings of The Physiological Society

Physiology 2015 (Cardiff, UK) (2015) Proc Physiol Soc 34, PC121

Poster Communications

Non-invasive assessment of retinal ganglion cell function using the electroretinogram: Data from healthy twin pairs

T. Shen1,3, A. Tariq3, T. Bhatti3, K. M. Williams1,3, C. J. Hammond1,3, O. A. Mahroo1,2

1. Ophthalmology, King's College London, London, United Kingdom. 2. Physiology, Development & Neuroscience, University of Cambridge, Cambridge, United Kingdom. 3. Twin Research and Genetic Epidemiology, King's College London, London, United Kingdom.

The electroretinogram (ERG) represents the summed electrical response of the retina to light stimuli, and can be recorded non-invasively from human subjects. The photopic negative response (PhNR) is a negative component of the waveform, elicited in response to full-field stimuli in photopic conditions, and has been shown to reflect retinal ganglion cell function, which is of interest both clinically and in research. The aim of this study was to perform a classic twin study of the PhNR, to obtain normative data and to explore relative genetic and environmental contributions to variation in the response. 106 healthy monozygotic (MZ) and dizygotic (DZ) twin pairs were recruited from the TwinsUK cohort, with local research ethics committee approval. Mean (SD) age was 62.5 (11.3) years. 93% were female and the majority were Caucasian (reflecting the cohort's demographic). ERGs were recorded in response to standard stimuli, corresponding to those recommended by the International Society for the Clinical Electrophysiology of Vision (ISCEV), using a conductive fibre electrode placed deep in the lower conjunctival fornix. The PhNR was quantified by measuring the ERG amplitude 65 ms after delivery of the photopic 3 cd m-2 s white flash (through a pharmacologically dilated pupil). The amplitude was measured from baseline, which was defined as the average over a time window of 20 ms prior to flash delivery. Approximately 150-180 repetitions of the stimulus were performed in photopic conditions (in the presence of a 30 cd m-2 white background), with responses averaged (from the right eye). Traces were excluded in cases of significant noise or blink artefact. Heritability was calculated using maximum likelihood structural equation modelling (OpenMx package). Responses were included from 196 twins (51 MZ and 47 DZ pairs). The mean (SD) amplitude was -14.6 (4.8) microvolts, and the range was -0.4 to -33.6 microvolts. Correlation coefficients within twin pairs were 0.32 for MZ pairs and 0.15 for DZ pairs, and the point estimate of heritability was 30.2%. Our study provides normative data for the PhNR when recorded with the fibre positioned low in the conjunctival fornix (though the range may not be generalizable outside the demographics of our cohort or with different methods of recording). This study is the first to explore the PhNR in twin pairs: the intra-pair correlation coefficient for MZ twins was double that for DZ twins; our findings suggest that 30% of the variation in the PhNR, as measured in this study, may be due to genetic factors.

Where applicable, experiments conform with Society ethical requirements