Alterations of visual contrast sensitivity in Parkinson's disease.

Contrast sensitivity functions were determined in a population of 18 patients suffering from Parkinson's disease, and compared with the data obtained in an age-matched group of healthy controls. The controls were more sensitive at all spatial frequencies tested than the patients. The statistical comparisons were highly significant, indicating general differences between the PD patients and the controls not related to individual spatial frequency channels. When comparing the sensitivity loss between low and high spatial frequencies no significant differences were found suggesting that the decrease in contrast sensitivity is a global effect. We controlled for effects of age and cerebral atrophy, and our findings cannot be accounted for by these factors. In addition, the amount of contrast sensitivity loss was not correlated with the severity of the disease. These global functional alterations appear to be related to the reduction of dopamine at various sites of the visual system.