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Muen Yang, Mitchell W Dul, Romain Bachy, Qasim Zaidi; Dynamic color and brightness adaptation abnormalities in early stages of glaucoma.. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5123.
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© ARVO (1962-2015); The Authors (2016-present)
Previous electrophysiology studies have shown that primate retinal ganglion cells (RGC) exhibit subtractive adaptation to prolonged stimuli (Zaidi et al. 2012). We were interested to know if early stages of glaucoma, a disease that affects RGC, causes color adaptation abnormalities. We measured adaptation to three cardinal color axes: yellow-blue, red-green, and achromatic light-dark, that targets konio, parvo, and magno RGC respectively.
10 glaucoma patients with MD better than -4 dB on a 24-2 HVF and 10 age matched controls were recruited. For one eye of each participant, we measured the speed and magnitude of adapting to 1/32 Hz color modulations along the three cardinal axes at central fixation, 8 degrees supra-temporal, supra-nasal, infra-temporal, and infra-nasal. Initially the perception followed the stimulus, but then accelerated to perceive gray before the stimulus physically reached this state. The stimulus' physical contrast at this point was called the "Nulled-Contrast:" a smaller value represented weaker and slower adaptation. Each subject was presented a total of 75 trials.
For each location and color axis, the mean adaptation difference between glaucoma and controls were small and did not reach statistical significance. However, in 12/15 comparisons, adaptation was weaker and slower for the glaucoma group. The probability of this happening due to chance was moderately low at 1.76% (binomial cumulative distribution with p=0.5), providing good evidence against assumption of no difference. To visualize individual data points, we plotted the Nulled-Contrast of every glaucoma subject against its age-matched control for each location and color axis. The majority of points (96/150) were above the unit diagonal, implying that in general glaucoma had weaker adaptation. The probability of no difference between glaucoma and controls was 0.038% (binomial cumulative distribution with p=0.5), which advocated strongly against no difference.
Early glaucoma patients may have weaker neural adaptation than normal. However, due to the early stage of the disease, adaptation abnormalities may be too mild to be significantly different than controls. We will compare the results with structural (OCT) and functional (10-2 visual field) data to obtain further insights.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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