Visual dysfunction in Parkinson's disease

Several abnormalities of visual function have been demonstrated in Parkinson's disease (PD) by both electrophysiologic and psychophysical testing. Prolonged visual evoked potential latencies and abnormal electroretinographic patterns, both of which respond to levodopa therapy, have been demonstrated in Parkinson's disease patients and in primates with experimental parkinsonism suggesting that retinal dopamine deficiency is an important factor in the pathogenesis of PD visual dysfunction. Abnormalities of color perception, especially in the blue-green axis, and of visual contrast sensitivity (VCS) have also been well documented in PD patients. Although VCS impairment is likely related to retinal dopaminergic dysfunction, the fact that this visual abnormality is orientation-specific raises the possibility of visual cortex involvement as well. Visual abnormalities in PD are usually clinically occult and not likely to be uncovered during a routine neurological examination or by ordinary high contrast visual acuity testing. The clinician must be aware, however, that several forms of disability ranging from gait freezing to visual hallucinations may be linked to an underlying impairment of visual function in Parkinson's disease.