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Optical Flow Perturbation Effects on Standing Balance in People with Multiple Sclerosis

Multiple sclerosis is a progressive disease that affects 2.5 million people by obstructing nerve signals, causing balance deficits. In three months, 56% of people with multiple sclerosis (PwMS) experienced falls. The purpose of this study is to examine the effects of visual perturbations on standing balance in PwMS. We hypothesized that visual perturbations would affect standing balance in PwMS more than control participants. Secondly, we hypothesized that standing balance would respond more to anterior-posterior perturbations than medial-lateral perturbations in PwMS. Fourteen PwMS and fourteen age-matched controls stood on a force plate under four 1-minute virtual reality conditions: medial-lateral perturbations, anterior-posterior perturbations, eyes open without perturbation and eyes closed. We calculated standard deviation and range of the center of pressure (COP) and ran repeated measures ANOVA with post hoc, pairwise comparisons. Compared to the medial-lateral perturbations, anterior-posterior perturbations more greatly impacted all subjects’ medial-lateral range and standard deviation of COP to the eyes-open control trial. Our first hypothesis was not supported, since perturbations did not affect standing balance in PwMS more than the controls, possibly because the PwMS were young (age: 38.9 years) and fit (preferred walking speed: 1.29 m/s). Prior research suggests that optical flow perturbations better reveal balance deficits in PwMS during walking than during standing, which is consistent with PwMS relying on vision for balance more during walking. Our second hypothesis was supported, as medial-lateral range and standard deviation were higher during anterior-posterior perturbations. Overall, these findings have implications for clinical screening of PwMS to detect fall risk.