Abstract
Purpose::
Monocular blur may cause a reduction in contrast sensitivity by binocular inhibition and has been shown to increase stereoacuity thresholds more than binocular blur of the same magnitude. When negotiating obstacles/steps under conditions of binocular blur subjects adopt a strategy of increasing toe clearance to reduce the risk of tripping, but as yet no studies have investigated if monocular blur will lead to a similar adaptation. The present study determined how toe clearance and stepping kinematics was affected by monocular blur or occlusion.
Methods::
14 healthy subjects (age 25.8±5.64) with normal vision walked along the laboratory onto a raised surface. Trials were performed with optimal refractive correction, 2 dioptre blur over the dominant or non-dominant eye or the dominant eye occluded. Foot placement and limb kinematics were analyzed via 3D motion analysis.
Results::
Stereopsis was reduced to 257secs of arc (dominant eye blurred) and 153 secs of arc (non-dominant eye blurred). Analysis shows an 18% (p<0.001) increase in vertical toe clearance when the dominant eye is blurred but only a 10% increase (p<0.001) when the non-dominant eye was blurred. The trail (support) foot was placed further from the step (p<0.001) and knee and hip flexure increased when each eye was blurred or the dominant eye occluded.
Conclusions::
We conclude that a relatively small amount of monocular blur (which leads to a reduction in stereopsis) can cause uncertainty in locating the step edge and increase vertical toe clearance to increase margins of safety. Blur in front of the dominant eye had a greater effect on step adaptations to blur in front of the non-dominant eye.
Keywords: vision and action • binocular vision/stereopsis • spectacle lens