Visuospatial dysfunction in the neurodegenerative diseases.

Visuospatial dysfunction is not generally considered a cardinal feature of the common neurodegenerative disorders of late life like Alzheimer's disease (AD), Parkinson's disease (PD), and Dementia with Lewy bodies (DLB). However, a large number of research studies have shown visually related disorders to be surprisingly pervasive among these disease states. Broader recognition of the problems is hindered by a complex literature, which suffers from a lack of uniform definitions of what constitutes "visuospatial" dysfunction and few commonly accepted theoretical models for interpreting results. The interface between visual-spatial function and other variably-defined constructs such as attention and executive function further complicates experimental approaches to this construct. Nonetheless, this review addresses both theoretical and practical issues regarding the presence, importance, and correlates of visual dysfunction associated with neurodegeneration. In addition, the functional impact of the deficits is addressed.