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Jia Jia Lek, Algis Vingrys, Allison McKendrick; Glaucoma alters rapid contrast adaptation. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3964.
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© ARVO (1962-2015); The Authors (2016-present)
The visual system quickly and efficiently adapts to changes in contrast, often with changes in fixation. The neurobiological mechanisms underpinning contrast adaptation are located at multiple sites within the visual pathways, with a key site at the retinal ganglion cell (RGC) dendrites. Early degenerative changes to RGC dendrites are a feature of glaucoma; hence we hypothesised that functional measures of contrast adaptation may be abnormal early in the disease. This study investigates if the magnitude and timecourse of recovery due to fast contrast adaptation is altered in glaucoma using a contrast detection task. We also explored whether facilitation and masking adaptation effects on contrast discrimination are altered in glaucoma.
15 people with glaucoma (mean age±SD: 66yrs±7) and 17 controls (62yrs±6), all with normal standard automated perimetry (SAP) measures within the central 4° participated. Central contrast detection and discrimination thresholds were measured for briefly presented (94ms) Gabor patches (1°x1°, 2cpd) with and without adaptation to patterns (1s, 2cpd, 50%contrast). The magnitude and timecourse of detection threshold elevation post-adaptation was assessed for varying interstimulus intervals (ISI: 47, 106, 200, 400, 600, 1000ms) between the adaptor and target. The magnitude of discrimination threshold changes was assessed for varying contrast relationships using targets below (30%), equivalent (50%) or above (70%) the adaptor.
Unadapted contrast detection (p<0.0001) and discrimination (p<0.0001) thresholds were elevated in the glaucoma group. Contrast detection thresholds (normalised to unadapted thresholds) of the glaucoma group were less affected by adaptation for ISIs: 47, 106, 200ms (p=0.02), returning to unadapted threshold earlier (~200ms) than controls (~400ms). Contrast discrimination data (normalised to unadapted thresholds) demonstrated similar between group facilitation effects for targets below (p= 0.3) and above (p=0.21) the adaptor. The glaucoma group showed less masking when the target was equivalent to the adaptor (p=0.023).
The glaucoma group demonstrated elevated macular contrast detection and discrimination thresholds without adaptation. Reduced adaptation effects in the form of masking immediately post-adaptor indicate altered fast contrast adaptation in glaucoma. These findings imply central vision abnormalities in natural visual experiences that are not captured by SAP.
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