What Drives Adaptive Gait Changes to Acutely Presented Monocular Blur?

Abstract

Purpose. To determine whether gait alterations due to monocular spherical lens blur were a safety strategy or driven by lens magnification. Methods. Adaptive gait and visual function were measured in 10 older adults (mean age, 74.9 4.8 years) with the participants' optimal refractive correction and when monocularly blurred with 1.00 DS and 2.00 DS lens over the dominant eye. Adaptive gait measurements for the lead and trail foot included foot position before the raised surface, toe clearance of the raised surface edge, and foot position on the raised surface. Vision measurements included binocular visual acuity, contrast sensitivity, and stereoacuity. Results. Equal levels of monocular positive and negative spherical lens blur led to very different stepping strategies when negotiating a raised surface. Positive blur lenses led to an increased vertical toe clearance and reduced distance of the lead foot position on the raised surface. Negative lenses led to the opposite of these changes. Conclusions. Findings suggest that step negotiation strategies were driven by the magnification effect provided by the spherical lenses. Steps appeared closer and larger with magnification from positive lenses and further away and smaller with minification from negative lenses and gait was adjusted accordingly. These results suggest that previously reported adaptive gait changes to monocular spherical lens blur were not safety strategies as previously suggested but driven by lens magnification. The significance of these findings in terms of prescribing large refractive changes in frail older patients is discussed.