Objective: To conduct a comprehensive assessment of visual processing in PD-ND, including tests of low-level vision sensitive to retinal pathology, high-level object/spatial vision reflecting ventral/dorsal visual pathway integrity, and to explore the relationship between executive dysfunction and visual impairment.

Background: Impairments in contrast sensitivity, color vision, attention, and eye movement control have been implicated as possible underlying causes of visual complaints in PD. Defective visual processing could have a negative impact on quality of life, but this topic has received relatively little attention in the literature.  

Methods: Thirty-five PD-ND and 41 healthy controls completed the study. Low-level vision was evaluated using a variable contrast acuity eye chart and the Farnsworth-Munsell color vision test. Ventral pathway tasks included reading single words, naming familiar objects/famous faces, and matching unfamiliar faces varying in single features vs. global configuration. Dorsal pathway/spatial exploration tasks included cancellation (lines, letters, shapes), King Devick test of rapid number naming, and locating objects/people in photographs. Frontal executive function was assessed by the anti-saccade test. Purdue pegboard and UPDRS were used to evaluate motor function.

Results: PD-NDs performed worse than controls on contrast sensitivity and color vision tests. On the ventral pathway tasks, PD-NDs were impaired in matching unfamiliar faces and performance correlated with reduced contrast sensitivity. PD-NDs were significantly slower on all dorsal pathway/spatial exploration tasks and showed enhanced sensitivity to task difficulty. Executive measure from anti-saccade test correlated with all dorsal pathway tasks even after controlling for bradykinesia. Executive dysfunction also correlated with color vision, but not with any of the ventral pathway tests.

Conclusions: Defective top-down executive control of attention in PD-ND contributes to impairments on dorsal pathway/spatial exploration tasks, but has little effect on ventral pathway/object recognition tasks. Ventral pathway deficits are only apparent in perceptually demanding tasks and may be attributable to reduced contrast sensitivity.  Farnsworth-Munsell test requires executive control of attention and is not an ideal test of color vision in patients with executive dysfunction.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/cognitive-mechanisms-of-visual-dysfunction-in-non-demented-pd-patients-pd-nd/