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Shira Radner, Robert Ennis, Barry Lee, Mitchell Dul, Qasim Zaidi; Adaptation abnormalities in Primary Open-Angle Glaucoma. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3939.
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Dynamic color and brightness adaptation are crucial for visual functioning. Does the effect of Glaucoma on retinal ganglion cells compromise these functions? Zaidi, Ennis, Cao, & Lee (Neural locus of color afterimages. Current Biology, 22(3), 220 - 224, 2012) used psychophysics and in vivo single-cell recordings to show that ganglion cells are the adaptation locus for color afterimages at moderate intensities. We used the same procedure to test the hypothesis that adaptation is weaker in patients with glaucoma (POAG) compared with age-matched controls.
On a CRT at a distance of 83 cm, a 4° central disk was divided into two halves. Beginning and ending at mid-grey, sinusoidal half-cycles slowly modulated the colors of the hemi-disks for 16 sec at 1/32 Hz to opposite ends of the cardinal axes (red-green, yellow-violet and white-black) that respectively isolate parvo, konio and magno ganglion cells (Sun, Smithson, Lee, and Zaidi, Specificity of cone inputs to macaque retinal ganglion cells. J. Neurophysiology, 95: 837-849, 2006). Observers perceived the difference between the two colors as first increasing and then decreasing to identity, followed by increasing and decreasing differences between the complementary colors forming an afterimage. Due to ganglion cell adaptation, the identity point preceded the end of the physical modulation, and the physical contrast at that point estimated the magnitude of adaptation. A second 2° circle was presented as a clock with a central dot as the fixation point, at either the central location or peripherally at 8° left, right, top or bottom. Observers used the clock to report the time of the identity point and a button press to report the end of the afterimage. We measured identity points and afterimage durations for the affected eyes of 13 POAG patients and 15 age-matched controls. The 5 fixation locations times the 3 cardinal axes were presented in random order, with 3 repetitions.
In 14 out of the 15 comparisons (locations x colors), mean identity points were later for glaucoma patients than for controls (probability of chance occurrence < .0001). All observers reported prolonged afterimages, but the measurements were noisier, and differences in duration were not significant.
Neural adaptation is slower in glaucoma patients for all three classes of retinal ganglion cells.
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