Visual influence on center of contact pressure in advanced Parkinson's disease.

The visual influence on upright posture was studied in seven patients with Parkinson's disease (PD), Yahr stage III to IV, and seven age-matched controls. The position of the center of contact pressure (CCP) between the feet and floor was analyzed by a photoelastic method. When the patients' eyes were closed, the CCP position shifted significantly backward in PD (open, 48.6 +/- 7.6%; closed, 45.0 +/- 4.8%; p < 0.01), whereas in controls, it shifted significantly forward (open, 45.5 +/- 5.8%; closed, 48.9 +/- 2.8%; p < 0.05). PD patients put their body weight less on the more affected foot (open, 49.6 +/- 4.5%; closed, 47.0 +/- 4.8%; p < 0.01) and more on the less affected foot (open, 50.4 +/- 4.5%; closed, 53.0 +/- 4.8%; p < 0.005), when the eyes were closed. Visual information is important in maintaining the upright posture in PD patients.