Investigating balance in persons with Down Syndrome: A focus on vision

BACKGROUND AND AIM: People with Down Syndrome (pwDS) exhibit poor balance and incoordination1, both features which have been linked to cerebellar disease pathology, peripheral and central sensory processing abnormalities, problems with tone and co-contraction and cognitive limitations2–4. This study explored the effects of visual and proprioceptive stimulation and increased cognitive load on balance in DS. METHODS: 12 pwDS and 12 matched typically developed healthy controls (TDhc) were tested whilst standing under 5 conditions: c1. Eyes open, c2. Eyes closed, c3. Eyes closed with enhanced under-foot texture, c4. Eyes open with a dual task (button press when a visual target changed colour), c5. Eyes open with optokinetic stimuli (OKS) back-projected onto a 3x2.5 metres screen. In all conditions projected fixation points standardised the pre-trial visual environment. Motion analysis (Codamotion) recorded postural sway (C7 vertebral level). Mean sway speeds were averaged over trial repeats and normalised to subject height. For conditions 1-4 mean sway over two 40 s collection trials were measured. In condition 5, ten 20s OKS trials induced balance perturbations and sway response speeds were calculated from 0.2-2s following stimuli onset. Responses under different sensory/cognitive conditions were normalised to the relevant baseline sway condition (quotients). Results were analysed using unpaired t-tests (SPSS version 7). RESULTS: PwDS swayed faster than TDhcs in all standing conditions and in response to OKS (figure 1). Quotients (Vision: c2/c1, texture: c3/c2, cognitive load: c4/c1 and OKS: c5/c1) were not statistically significant between groups (figure 1B). In pwDS response magnitude following OKS was significantly correlated with baseline sway speeds with eyes open (r=0.703, p=0.011). TDhcs OKS responses did not correlate with baseline sway. CONCLUSIONS: The tendency for sway to be similar under eyes open and closed conditions in pwDS suggests impaired use of vision for the stabilisation of balance. However, the lack of group differences with the quotients and the correlation between response size and baseline sway in DS suggests that greater instability under many sensory and cognitive conditions may be related to increased baseline sway rather than specific sensory processing deficits or problems with cognitive loading. 1. Shumway-Cook & Woollacott (1985) Dynamics of postural control in the child with Down syndrome. PhysTher 65, 1315–22. 2. Costa (2011) An assessment of optokinetic nystagmus (OKN) in persons with Down syndrome. Exp Brain Res. 214, 381–91. 3. Carvalho & Almeida (2009) Assessment of postural adjustments in persons with intellectual disability during balance on the seesaw. J Int Dis Res 53, 389–395. 4. Vuillerme et al. (2001) Assessment of Static Postural Control in Teenagers With Down Syndrome. Adapt Phys Act Quart 18, 417–433.