Parkinson's disease (PD) has traditionally been viewed as a movement disorder characterized by tremor, rigidity, akinesia, and impaired posture and gait, but more recent work documents a range of concomitant non-motor symptoms including changes in sensation, perception, and visuospatial cognition. PD subtypes are defined by characteristics of motor symptoms at disease onset, such as type of symptom (tremor, non-tremor) and body side of symptom onset, but the nature of the non-motor symptoms accompanying these subtypes is relatively unknown. The first two studies explored visual perceptual and spatial function in relation to PD subtypes. PD patients with non-tremor symptoms at onset were hypothesized to perform more poorly than those with tremor onset because of greater cortical and subcortical neuropathology. Patients with symptoms starting on the left side of the body were hypothesized to perform more poorly than right-onset patients on visuospatial functioning, reflecting hemispheric asymmetries in dopamine levels. The third study examined an intervention to counteract visual deficits relevant to activities of daily living (ADLs) in PD in general.

Study 1 used a self-report measure to identify which visual domains are most affected in PD subtypes, as well as objective measures of visual functioning. Patients with non-tremor onset, but not those with tremor onset, had impairments in contrast sensitivity and specific visual ADLs. Study 2 used a standard neuropsychological measure to assess visuospatial functioning in PD subtypes. Patients with left-side motor symptoms at onset and non-tremor symptoms at onset performed significantly more poorly than the control group. Study 3 examined the effect of visually-based environmental enhancements on five instrumental ADLs in PD and control participants. These enhancements improved performance on specific ADLs in both groups.

The present studies provided evidence for reduced contrast sensitivity, worse visuospatial functioning, and more self-reported problems with visual ADLs in the non-tremor PD subtype than in those with tremor at onset, and worse visuospatial functioning in patients with left than right motor symptoms at onset. Characterizing perceptual and cognitive changes in PD subtypes provides a more complete picture of the disorder. Future studies should focus on the relation between these changes and ADLs in PD subtypes.