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    This small study adds to a growing body of work suggesting that glaucoma affects visual processing in ways that are not necessarily seen on visual field (VF) testing.

    There is evidence that people with glaucoma exhibit difficulties with some complex visual tasks such as face recognition, motion perception and scene exploration. The purpose of this study was to determine whether glaucoma affects the ability to categorize briefly presented visual objects in central vision at 2 different levels of contrast.

    The authors chose 14 patients with glaucoma (primary open-angle and preperimetric) who still had intact central visual fields. They used stimuli of two contrast levels (50% and 100%). The decreased contrast was designed to mimic a situation of fog, dazzling sun or shadowy light, as well as at dusk and dawn.

    Accuracy was significantly decreased for the medium contrast stimuli in patients with glaucoma compared with normal controls (87% vs.  94%, P=0.046). Group average response times were also significantly slower in glaucoma patients, at 712 ms compared with 643 ms for controls (P<0.01).

    Performance was equivalent in the two groups when the picture contrast was 100%.

    The impairment observed in the categorization task supports previous work that demonstrates that people with glaucoma can have greater difficulties with complex visual tasks. Further work is required to determine whether the deficits described here are related to structural cortical alterations in glaucoma, or whether they precede such changes.