Visually Induced Postural Sway in Elderly Fallers

Participants will undergo the Fallscreen from the Physiological Profile Assessment (PPA) (Lord, Menz, & Tiedemann, 2003) to assess their risk of falling. FallScreen is a falls risk calculator and is designed as a comprehensive instrument suitable for Rehabilitation and Physical Therapy and Occupational Therapy settings and for dedicated Falls Clinics. It takes 45 minutes to administer and contains 15 items: three assessments of vision (high and low contrast visual acuity and edge contrast sensitivity), three assessments of peripheral sensation (tactile sensitivity, vibration sense and proprioception), assessments of three lower limb muscle groups (knee extensors, knee flexors and ankle dorsiflexors), assessments of both hand and foot reaction time and four assessments of body sway (sway on floor and foam with eyes open and closed). The Roll Vection Test (RVT) (Lord and Webster 1990) will be used to assess visual dependence under a visually challenging situation. The system consists of an opened umbrella, 125cm in diameter, with 8 alternating black and white panels. The umbrella is mounted horizontally onto a height adjustable stand. During the test the umbrella is rotated at 16rpm. Attached is a smaller flat white disc (21cm diameter) uncoupled from the rotation of the umbrella. The disc extends out from the inner surface of the umbrella to about level with its rim. The white disc is marked with a straight black line across its centre. The subject will stand within arms reach of the disc, with the height of the axis of rotation of the umbrella and disc adjusted to eye level. At the start of the test the white disc is positioned so that the black line is offset by 26 degrees from vertical. After 30 seconds of rotation the subject will be asked to align the small disc so that the black line is vertical. The offset from vertical will be measured with a digital spirit level. Any offset over 4 degrees is defined as abnormal, and 6.5 degrees is defined as high risk of visual dependence. Once this has been completed, each participant will be asked to stand on force plates in front of an ImmersaDome. The immersadome is a 2 meter wide freestanding dome that gives the feeling of being in a three-dimensional virtual environment (Immersadome information sheet attached). The Immersadome will be positioned directly in front of the subject, up on blocks to ensure that it covers more than 130 degrees of the subjects’ visual angle (Dichgans et al., 1972). The experiment will begin with the subject standing on a force plate while measurements are taken under 6 conditions, - feet apart (10 cm apart) eyes open, - feet apart (10 cm apart) eyes closed, - feet apart (10cm apart) and 4 different optokinetic visual stimuli (2 moving designs in opposing directions) projected onto the immersadome. Stimulus 1 is a roll vection clockwise and anticlockwise, and Stimulus 2 is a ‘moving through Hallway’ forwards or backwards. During all balance tests a physiotherapist will be positioned next to the participant for safety purposes. Postural sway will be measured using centre of pressure pathway. We will be comparing the size of postural sway between dizzy and non dizzy subjects. We will also compare subjects with higher and lower scores of visual dependance. The full testing session, including the fallscreen, will take approximately 90 minutes to administer, and only occurs once.