Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCB305

Poster Communications

Exploration of contributions from retinal pigment epithelium and retinal ganglion cells to the "Light Adaptation Effect" of the human photopic electroretinogram

X. Jiang1, Z. Xu1, C. J. Hammond1, O. A. Mahroo2,1,3

1. Ophthalmology, King's College London, London, United Kingdom. 2. Institute of Ophthalmology, University College London, London, United Kingdom. 3. Physiology, Development and Neuroscience, University of Cambridge, Cambridge, United Kingdom.

The electroretinogram (ERG) represents the electrical response of the retina to light, and can be recorded non-invasively in vivo. The "Light Adaptation Effect" (LAE) refers to the growth in amplitude of the photopic electroretinogram elicited by light flashes delivered over several minutes after onset of a photopic, rod-saturating light background. The processes underlying this effect are not understood. An increase in potential is known to occur over the retinal pigment epithelium (RPE) over a similar time course. Also, intrinsically photosensitive retinal ganglion cells have been shown, in animal models, to affect the light-adapted ERG. We compared the time course of the LAE in three healthy subjects with that recorded in two patients: one patient had a genetic condition (Best disease) that abolished the increase in potential over the RPE; the other patient had loss of ganglion cells in one eye. The study had research ethics committee approval. In each experiment, the subject dark adapted for 20 minutes and was then exposed to a white background (30 photopic cd m-2). White flashes (3 photopic cd m-2 s) were delivered (in groups of 36 flashes, repeated every 2 minutes) for the next 20 minutes. Pupils were pharmacologically dilated. ERG responses were recorded using a conductive fibre electrode placed in the lower conjunctival fornix. ERG b-wave amplitudes were measured and plotted as a function of time following onset of the white background. In the healthy subjects, the b-wave amplitude rose with time after background onset, reaching a plateau at approximately 10 minutes. The ratio of the amplitude at 20 minutes to the initial amplitude ranged from 1.8 to 2.0. The time course of the increase in b-wave was similar in the patients. The ratio was 2.0 in the patient with Best disease. In the patient with unilateral loss of ganglion cells, the ratio was 1.9 in the affected eye and 2.0 in the healthy eye. We found that the LAE was present in both patients, and followed a similar time course to that seen in healthy subjects. Thus, the processes underlying the LAE appear not to depend on the increase in potential over the RPE despite the two having similar time courses. Also, loss of ganglion cells does not seem to affect the LAE, suggesting that the effect does not depend on ganglion cell function.

Where applicable, experiments conform with Society ethical requirements