Conclusions: This study suggests that patients with Parkinson's disease (PD), even in the early stages, have decreased body limits of stability (LOS) and changes in the visual input impair their postural control.
Objective: To assess the LOS and the postural responses after changes in visual input in a group of PD patients in stage 1 of the Hoehn and Yahr classification.
Subjects and methods: Twenty PD patients in stage 1 and a group of 24 normal subjects as control were assessed in two tests: (1) the LOS and (2) measurement of the body center of pressure area (COP) 10 s before and after sudden change in visual flow velocity. We also investigated labeling of the COP trajectory in these two periods. The stimulation paradigm was a horizontal optokinetic stimulation (60 degrees /s and suddenly stopped) using a virtual reality system.
Results: LOS showed significant decrease in PD patients as compared with the control group (p<0.001, Kruskal-Wallis and Wilcoxon ranked test). The COP values increased significantly (p<0.001, Wilcoxon signed rank test) after sudden changes in the visual flow velocity in relation to the control group. After the visual stop the PD patient showed a spatial 'roaming' approaching the limits of stability and therefore impairing the postural control.