Spatial contrast sensitivity is reduced in bilateral Parkinson's disease.

We studied the contrast sensitivity functions of 41 patients with idiopathic Parkinson's disease (PD) with a wide range of parkinsonian symptomatology (Hoehn and Yahr stages 1 to 4) and 22 age-matched control subjects in a parametric design. Results demonstrated reduced contrast sensitivity in PD patients but only in those patients who had progressed beyond Hoehn and Yahr stage 1. Furthermore, there were deficits in contrast sensitivity related to the severity of PD.