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D. B. Elliott, L. Johnson, C. Harley, J. Buckley; Stepping Adaptations When Negotiating a Raised Surface: A Comparison Between Multifocal and Single Vision Spectacles in the Elderly. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1569.
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Epidemiological evidence indicates that elderly multifocal-wearers are at increased risk of falling, especially on curbs or stairs. Yet little is known regarding stepping strategies used by elderly multifocal-wearers during transitions between levels. The purpose of this study was to determine the effects of wearing multifocal compared to single distance vision spectacles upon stepping characteristics and toe clearance parameters when negotiating a raised surface.
Nineteen healthy older adults (72.7 ± 4.2 yrs) repeatedly approached and stepped up and along a raised platform (14.9 cm high, 3 m long, 1 m wide) the height of which was randomly increased by 1.0 cm or decreased by 0.6 cm every fourth trial, whilst wearing bifocal, varifocal or single distance vision spectacles. Toe clearance parameters and step characteristics from lead limb heel contact before the platform until lead limb foot contact on the platform were assessed using a 6-camera, Vicon motion analysis system.
When wearing multifocal compared to single distance vision spectacles the trail limb was placed further from the platform (p=.05). Consequently the lead foot crossed the raised edge later in swing phase and the foot landed closer to the step edge when wearing bi- or varifocals (p = .003). Vertical toe clearance also increased (p<.001) which may have been due to the changes in trail foot placement and/or the increased ankle dorsi-flexion found in the multifocal conditions (p=.01). Forward centre-of-mass velocity at foot contact during the penultimate and crossing steps was reduced when wearing multifocal compared to single vision spectacles (p=.01), and there was an increased incidence of ‘inadvertent’ heel (but not toe)-step contacts (p=.03).
Toe clearance and foot placement strategies when negotiating a raised surface are adapted when wearing bi- and varifocal compared to single distance vision spectacles. This suggests that the optical effects inherent in their design result in unreliable visual information regarding the exact location and dimensions of a raised edge. Although the adaptations utilised ensured vertical toe clearance increased, the increase in heel contacts (which unlike a toe contact would likely not result in a trip) suggest subjects may have adopted this strategy to increase propreoceptive feedback.
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