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Tad Daniels, Joost Felius, David G Birch, Karl G Csaky; Threshold versus Area Assessment to Determine Aspects of Rod Photoreceptor Loss in Subjects with Age-Related Macular Degeneration (AMD).. Invest. Ophthalmol. Vis. Sci. 2016;57(12):3709. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Scotopic sensitivity is decreased in AMD. The goal of the present study is to determine if adjusting scotopic microperimetry stimulus size can detect deficiencies in summation of the inner retina or detect patches of decreased rod sensitivity.
One eye from patients with early AMD (n=7), intermediate (n=13), geographic atrophy (n=8), and one eye from normal subjects (n=5) was examined. Following 30 minutes of dark adaptation, scotopic sensitivity was measured at 56 locations within 10° of the fovea aligned to OCT using a modified fundus microperimeter (MP-1S, Nidek Technologies) and neutral density filters to adjust the dynamic range to the individual’s mean sensitivity. Patients were tested with both spot size 3 (0.43°) and 5 (1.72°) stimuli, and the pointwise threshold differences (in dB) were evaluated. Points falling on patches of geographic atrophy were eliminated from analysis. A linear summation model predicts a 12 dB threshold difference in sensitivity between spot sizes 3 and 5, while probability summation predicts a 3 dB threshold difference. Threshold differences >12 dB would indicate partial, patchy rod loss.
In the normal, median sensitivity across the 20° was 41.2±1.6 dB and 29.0±1.2dB, respectively for the size 5 and size 3 stimuli. In the patients with AMD, no significant effects of disease stage were found. Median sensitivities were reduced to 32.4±4.3 dB and 18.8±5.0 dB, for spot sizes 5 and 3, respectively. The mean pointwise threshold difference between the size 5 and size 3 stimuli in both normals (11.8 dB) and patients (12.7 dB; P=0.8) was compatible with the linear summation model.
Under these test conditions, the stimulus sizes 3 and 5 were sufficiently small to avoid effects of probability summation. Patients with AMD showed decreased sensitivity but maintained a ~12-dB threshold difference between the size 3 and size 5 test conditions, consistent with a uniform, rather than patchy, loss of rod photoreceptors.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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