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G. K. Panesar, B. T. Barrett, I. E. Pacey, M. J. MacLellan, J. G. Buckley; Amblyopic Eyes Contribute Usefully to the Execution of Everyday Mobility Tasks. Invest. Ophthalmol. Vis. Sci. 2008;49(13):755.
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Monocular occlusion in visual normals has been shown to significantly affect gait parameters during obstacle negotiation (Patla et al., 2002, Exp Brain Res; 142; 551-561). However, it is not known whether naturally-occurring unilateral visual loss or compromised stereopsis similarly affects gait parameters. Here we determine if foot positioning and toe clearance during obstacle negotiation are adapted in individuals with amblyopia. By comparing performance under habitual viewing and monocularly-occluded conditions, we also determine the contribution of the amblyopic eye
7 amblyopic and 5 visually normal individuals performed repeated walking trials during which they negotiated a single obstacle placed in their travel path under three viewing conditions: 1) habitual viewing, 2) dominant eye occluded, 3) non-dominant eye occluded. Obstacle height (7, 15 or 22cms) and position within the travel path (varied by 10 to 40 cm) were randomised across trial repetition (n=6) to minimise learning effects. Contralateral limb foot positioning before the obstacle (Footpos) and vertical toe clearance (VTC) were determined via 3D-motion analysis
In both groups, monocular occlusion of either eye led to an increase in VTC relative to habitual viewing conditions (p <0.001). A significant group-by-obstacle height interaction existed (p=0.013); VTC increased with increasing obstacle height in amblyopes but decreased in the visual-normals. Footpos was not affected by group or vision condition (p>0.35), but increased with obstacle height (p=0.045).
Since VTC increased with increasing obstacle height in amblyopes but decreased in visual normals, our results indicate that amblyopes maintain margins of safety during adaptive gait. Amblyopes, therefore, may be habitually more cautious when performing gait tasks. Our finding of increased VTC in amblyopes when the amblyopic eye was occluded suggests that the amblyopic eye contributes usefully to the execution of everyday mobility tasks. Thus, as in visual normals, in amblyopes two eyes are better than one.
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