Abnormal psychophysical visual perception in Parkinson's disease patients.

Several visual dysfunctions in Parkinson's disease (PD) are described. Most of them are subtle or only demonstrated by stimulus-specific electrophysiologic or psychophysical testing. However, these minor deficits are thought to be of clinical relevance as they are related to direct or indirect complaints. Special emphasis is laid on visual hallucinations. These are most likely of multifactorial origin. The relation between hallucinations in PD and in dementia with Lewy bodies has to be elaborated further. Visual loss, as a possible and reversible cause of visual hallucinations should be actively sought and corrected as far as possible. An underlying role of dopaminergic retinal cells in visual dysfunction of PD patients is widely recognised. However, whether the basic abnormality resides also in the visual cortex remains to be elucidated. Other neurotransmitters may also be involved. It has not been answered whether visual dysfunction might distinguish PD from other forms of parkinsonism.