An Evaluation of the Effect of Vision on Standing Stability in the Early Stage of Parkinson’s Disease

Abstract

Background: Postural instability is a common disorder in Parkinson’s disease (PD). The aim of this study was to evaluate stance stability of the subjects at the early stage of PD with both linear and nonlinear approaches. Moreover, this study aimed to find the effect of visual control on quiet stance postural control in these patients. Method: Seventeen PD patients (Hoehn/Yahr scale: 1) and 17 healthy control subjects were instructed to maintain quiet postural stance in 2 conditions (opened eyes and closed eyes). Four linear (excursion, path length, velocity, root mean square) and 1 nonlinear (approximate entropy) center of pressure (COP) parameters were calculated. A 2 × 2 mixed ANOVA was used for the final analysis. Results: Although there was no difference between the stability of PD patients and healthy control subjects based on excursion of COP in both mediolateral (ML) and anteroposterior (AP) directions, other linear parameters (path length of COP sways, velocity of COP sways, and root mean square in both ML and AP planes) showed that PD patients were significantly unstable compared to normal subjects (p value < 0.05). Vision influenced the stability of both groups significantly. The interaction of vision and group was not significant based on linear and nonlinear stability parameters. Conclusion: Although patients in the early stage of PD seem to be unstable based on COP linear measures, their postural control system is still flexible to adapt to environmental perturbations in quiet stance and they are not more visually dependent than healthy subjects to control stability in this position.