Stereopsis and extrastriate cortical atrophy in Parkinson's disease: a voxel-based morphometric study.

Among the various visuospatial dysfunctions, deficits of stereopsis could be associated with Parkinson's disease. We examined differences in regional gray matter volume between Parkinson's disease patients with normal stereopsis and with abnormal stereopsis to delineate the possible anatomical correlate of stereopsis. Stereopsis was assessed using the Titmus test in 35 drug-naive patients with Parkinson's disease. Voxel-based morphometry was utilized to assess regionally specific differences in gray matter volume between 16 patients with normal stereopsis and 19 patients with abnormal stereopsis. Patients with abnormal stereopsis had a significant gray matter volume reduction in the right extrastriate visual cortex compared with patients with normal stereopsis (P<0.05, corrected for multiple comparisons). Voxel values extracted from the significant cluster in group comparison were negatively correlated with log seconds of arc of the Titmus test (Spearman correlation, P<0.001). Our results suggest that deficits of stereopsis are associated with nondominant extrastriate cortical atrophy and that abnormal stereopsis implicates the cortical visual dysfunction as part of the nonmotor symptoms in Parkinson's disease.