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Xiaofan Jiang, Shaun Leo, Isabelle Chow, Mathura Indusegaran, Anthony G Robson, Andrew R. Webster, Christopher Hammond, Omar Abdul Rahman Mahroo; Tracking Slowed Dark Adaptation Dynamically in Vitamin A deficiency and retinal disease by electroretinogram. Invest. Ophthalmol. Vis. Sci. 2020;61(7):5053.
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© ARVO (1962-2015); The Authors (2016-present)
Standard full-field electroretinograms (ERGs) assess retinal function at steady state, after light/dark adaptation. We delivered dim flashes following extinction of a light background to track recovery of rod system sensitivity electrophysiologically, making recordings in control participants and patients.
Participants’ pupils were pharmacologically dilated, and ERGs were recorded using conductive fibre electrodes in response to the standard ISCEV dim flash (DA 0.01; corresponding to 0.02 scotopic cd m-2 s) delivered over 30-60 min following extinction of the standard ISCEV photopic background. Each participant was exposed to the photopic background for an additional 5 min following standard photopic testing. Flash series were repeated every 2 min, and b-wave amplitudes plotted as a function of time in the dark (normalised to final level).
Eleven participants underwent the recording protocol, including 7 healthy volunteers (aged 21-82 years), a 50 year old with early onset widespread drusen, two patients (ages 42 and 49), with molecularly confirmed Sorsby Fundus Dystrophy (SFD) and a 70 year old with Vitamin A deficiency (VAD) after treatment and at varying levels of deficiency. Responses were initially of low amplitude after extinction of the background, but then recovered gradually in the dark. In all participants expect the SFD and VAD patients, recovery kinetics were broadly similar: amplitudes reached half the final level by c.10 min, and the final level at c.20 min. The VAD patient showed normal recovery following treatment, no recovery at all when markedly deficient, and a slowed recovery when more mildly deficient. The SFD patients displayed slowed recoveries, similar to that shown by the VAD when mildly deficient.
The protocol was well tolerated and yielded a discernible recovery curve in all participants. Slowed recoveries were seen in SFD and VAD. Although abnormalities in SFD on clinical examination are largely confined to the macula, these findings confirm delayed recovery affecting the retina as a whole, and are consistent with an “ocular vitamin A deficiency” in SFD. The protocol might have advantages over conventional psychophysical dark adaptation in being more objective and less reliant on patient concentration, and yielding recovery parameters reflecting the retina as a whole.
This is a 2020 ARVO Annual Meeting abstract.
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