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A.C. Kooijman, F.W. Cornelissen, T.P. Dryja, J.W. R. Pott; Impaired Perception of Moving High– and Low–Contrast Optotypes by Bradyopsia Patients Lacking RGS9 . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3710.
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© ARVO (1962-2015); The Authors (2016-present)
Subjects with the recently defined disease bradyopsia have a phototransduction defect caused by an inactive RGS9 gene. This defect delays the adaptation to a decrease in illumination. E.g., bradyopsia patients require 30 sec to recover normal ERG amplitudes after a bright light flash (normal < 2 sec). They describe difficulties in regular daylight, but the range and magnitude of the psychophysical consequences of their disease remain poorly understood. We studied the influence of luminance, contrast, and velocity on the visual resolution in bradyopsia patients to better understand their vision.
Four subjects with bradyopsia, all RGS9 W299R homozygotes, and 22 control subjects participated. Visual acuity (VA) vs. luminance (1–1200 cd/m2) was assessed with high contrast optotype charts. Dynamic VA (DVA) vs. velocity was assessed with a single optotype presented on a computer monitor. The optotype was either stationary or moving (2–25°/s). We used four Weber contrasts, 1.0, 0.1, –0.1, and –1.0, at three background luminance levels: 10, 30 and 100 cd/m2.
Patients’ VA increased with luminance up to 10 cd/m2 and decreased above it. In controls VA increased up to 100 cd/m2. In patients DVA decreased if luminance increased from 10 cd/m2 to 100 cd/m2; in controls DVA increased with luminance. Patients’ negative–high–contrast DVA was lower than positive–high–contrast DVA, where controls showed equal DVAs in both conditions. Patients’ low–contrast DVAs for positive and negative contrast were similar, but decreased with increasing luminance; in controls low–contrast DVAs increased with luminance. DVAs with increasing velocity showed large variations between patients.
Vision impairment in bradyopsia patients at 10 cd/m2 and above can be attributed to the delayed recovery from light. Likewise the lower negative–high–contrast DVAs can be explained. The identical DVAs for positive and negative low–contrast optotypes at 10 cd/m2 indicate a delayed adaptation to any change in retinal illumination at moderate light levels.
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