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Elena Rodrigo Diaz de Cerio, Jeremiah MF Kelly, David Carden, Ian J Murray; The benefits of a Red Background when measuring Dark Adaptation. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4312.
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Dark Adaptation (DA) is now accepted as important for the study of retinal health. The slope of the rod-mediated sensitivity recovery function, called S2, is particularly affected in aging and several diseases such as early age-related macular degeneration (AMD). DA has not been extensively studied in clinics because of the prolonged testing time and patient discomfort. Introducing a red background, which is blind to the rods, should theoretically reduce testing time and also be more acceptable compared with a black background. Here we test this idea in a novel digital set up, designed for application in a clinical setting.
A custom setup was used to measure DA curves in 11 subjects (mean age 32.5, sd 10.13 years). The test was performed four times under four experimental conditions using zero and three different red backgrounds (0.05, 0.10 and 0.20 cd.m-2 photopic) (λ max=655 nm). Following a localized bleach, (min 30%), a method of adjustment technique was used to respond to a flickering (4Hz) green stimulus (λ max= 530 nm) at 80 on the temporal retina.
Results: The time to rod cone break, sometimes called the alpha point, was significantly shortened when the red background was used. The mean alpha time decreased from 4.9 min, for the black background to 4.0 min for the highest intensity red background (p <0.001). Crucially the mean slope of the rod recovery, S2, (-0.29 (0.08) log10 (cd.m-2). min-1) was independent of background intensity (p= 0.39) and matched values in the literature. Cone threshold rose systematically as the red background increased (p<0.0001).
Conclusions: The addition of a cone-suppressing background allows significantly quicker measurement of S2 compared with no background and is also more acceptable to patients. Our technique has the potential to be useful for clinical measurements of rod function in older and diseased eyes, particularly in AMD where early diagnosis is important.
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