Vision in Parkinson's disease: what are the deficits and what are their origins?

Evidence for impairments of early visual processing in Parkinson's disease is reviewed. The review touches on some relevant anatomical and pharmacological studies and some studies of visual cognition in the illness, but is mainly concerned with human psychophysical and electrophysiological studies of spatial and temporal aspects of vision and of colour vision. Evidence from eye movement studies is also discussed for the light which it may throw on studies of early visual processing. It is concluded that, despite some difficulties in interpretation, there is good evidence for abnormalities of motion and colour perception, and probably of spatial vision also, but that present evidence does not compel us to look beyond the retina for the likely site of origin of these impairments.