The Effects of Vertical Yoked Prisms on Gait

Abstract

To investigate the influence of base down (BD) and base up (BU) yoked prism wear on gait. Gait was assessed in 31 young healthy adults (mean age, 24.0 ± 5.1 years) during and after wearing 5 prism diopter ((Δ)) BU yoked prisms, 5(Δ) BD yoked prisms, and plano (PL) (zero power; control condition) lenses, worn in a pseudorandom order. Velocity; cadence; step length; double support phase; step width; and variability in step time, step width, step length, and swing time were measured as participants walked at a freely chosen walking speed along a 5.3-m electronic mat placed in the center of a 7.5-m walkway. Gait parameters were analyzed for each viewing condition before, during, and after prism wear. BD yoked prisms, when compared with PL, led to slower velocity, lower cadence, decreased step length, and increased step time variability (P ≤ 0.001) These gait parameters did not significantly differ between BU yoked prisms and PL lenses (P > 0.05). Measurements taken immediately on removal did not differ from those taken after a time delay of 5 minutes. BD yoked prisms affected gait in young healthy adults walking across an unobstructed path at their freely chosen walking speed, in that participants adopted a slower, apparently more cautious gait pattern; BU yoked prisms did not significantly affect gait. The effect of BD prism on gait may be due in part to a perception of increased height.