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Habiba A. Bham, Simon D. Dewsbery, Jonathan Denniss; Glaucoma Affects Contrast Sensitivity but Not Apparent Contrast of Visible Stimuli. Invest. Ophthalmol. Vis. Sci. 2019;60(9):2464.
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© ARVO (1962-2015); The Authors (2016-present)
Reduced contrast sensitivity as measured by visual field (VF) tests is a hallmark of glaucoma, but how glaucoma affects the apparent contrast of visible suprathreshold images is unknown. We investigated the effects of glaucoma on the apparent contrast of suprathreshold stimuli of different spatial frequencies, presented both within and outside VF defects.
Twenty glaucoma participants with partial VF defects (mean age 72, standard deviation [SD] 7y) and 20 individually age-matched healthy controls (mean age 70, SD 7y) took part. First, we measured contrast detection thresholds for Gabor stimuli (SD=0.75°, random orientation, phase cycling at 1Hz) of 4 spatial frequencies (0.5, 1, 2, 4 cpd) presented at 10° eccentricity in a 2-interval forced choice procedure. For glaucoma participants, detection was measured both within and outside the VF defect. Participants then completed a contrast matching task using identical Gabor stimuli: Participants adjusted the contrast of a central Gabor to match that of a fixed-contrast reference Gabor presented in the same peripheral locations as for the detection task. Reference Gabor contrast was set at 2x and 4x detection threshold in separate conditions. Data were analysed by linear mixed modelling.
Compared to controls, glaucoma participants’ detection thresholds were raised by 5.0 ± 2.5% (standard error, p=0.12) and by 14.1 ± 2.6% (p<0.001) outside and within VF defects respectively. For reference stimuli at 2x detection contrast, matched contrast ratios (matched/reference contrast) were 16.0 ± 3.9% (p<0.001) higher outside compared to within VF defects in glaucoma participants. Matched contrast ratios within VF defects were similar to those in controls (mean 3.3 ± 6.6% lower, p=0.87). For reference stimuli at 4x detection contrast, matched contrast ratios were similar across all 3 groups (grand mean 1.07 [range 1.06-1.10], main effect χ2(2)=1.1, p=0.58). Spatial frequency had minimal effect on matched contrast ratios for 2x (χ2(3)=6.4, p=0.092) and 4x (χ2(2)=5.9, p=0.054) reference contrasts.
Despite reduced contrast sensitivity, people with glaucoma perceive the contrast of visible suprathreshold stimuli similarly to healthy controls. Our findings contradict common depictions of glaucoma showing areas of reduced contrast and suggest possible compensation for glaucomatous sensitivity loss in the visual system.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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