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A.M. McKendrick, D.R. Badcock, W.H. Morgan; Impairments in the Perception of Global Motion and Global Form in Glaucoma . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3715.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Impairments of pre–cortical visual processing have been well studied in glaucoma. Glaucoma should impair cortical visual processing due to reduced input from retinal ganglion cells, and also possibly due to abnormal cortical function. Visual processing is hierarchical whereby local stimulus attributes are combined into global percepts at latter stages of processing. Here we assessed whether cortically processed global percepts are disrupted in glaucoma in areas of visual field classified as normal using standard automated perimetry (SAP). Performance on global tasks (motion and form) was compared to measures of presumed pre–cortical magnocellular (M) and parvocellular (P) function in the same individuals. Methods: Fifteen control subjects and 12 people with primary open angle glaucoma participated. Testing was performed foveally and mid–peripherally (12.5°). Subjects with glaucoma were tested in a peripheral region of relatively normal visual field (neighboring locations required to be within the normal 95% confidence limit on the total deviation plot of their most recent SITA/full threshold Humphrey Field Analyzer assessment (Carl Zeiss Meditec, Dublin, CA). Control subjects were tested in matching locations. Contrast discrimination thresholds were measured using the steady–pedestal (M) and pulsed–pedestal (P) tasks of Pokorny and Smith. Global motion perception was assessed using global dot motion stimuli and threshold determined as the minimum dot percentage required to be moving in a common direction for the correct identification of that direction. Global form coherence thresholds were measured as the minimum percentage of coherent dot pairs necessary to detect structure in Glass patterns. Thresholds were measured using 99% contrast and low contrast stimuli (10x individual contrast thresholds for pattern detection to match visibility across observers). Results: Glaucoma patients demonstrated higher global motion and form coherence thresholds than controls in the mid–periphery (p<0.05). Different individuals performed poorly on the motion and form tasks. The subjects with the greatest presumed M deficits were those with the largest deficits on the global motion task. Conclusions: Some glaucoma patients demonstrate profound impairments of global processing in areas of visual field classified as normal using SAP. This finding implies that some people with glaucoma may have greater difficulty with complex visual tasks (for example: navigation through the environment or face recognition) than predicted by their visual field loss.
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