|Title||WHY MIGHT NEW SPECTACLE WEARERS FALL MORE OFTEN?|
|Author, Co-Author||David Elliott, Graham Chapman|
|Abstract|| PURPOSE: A randomized controlled trial recently reported that prescribing new spectacles increased falls rate in older people (Cummings et al., J Am Geriatr Soc, 2007). We wished to determine what factors might cause such an effect and whether this could be prevented.
METHODS: Ten subjects (mean age 77.1 ± 4.3 years) walked up to and stepped up onto a single step from two paces away. Their stepping strategies were analysed using an 8-camera 3-D motion analysis system (Vicon Motion Systems Ltd, Oxford). Their step negotiation was assessed under optimal refractive correction and with +2.00DS, +1.00DS, -1.00DS or -2.00DS binocular blur.
RESULTS: Mean binocular visual acuity was reduced from -0.11 logMAR (~20/15) to about 0.04 logMAR (20/22) with ±1.00DS and about 0.30 logMAR with ±2.00DS (20/40). However, stepping strategies were very different with the plus and minus blur lenses. For example, plus lenses led to an increased clearance of the step edge and minus lenses led to a decreased clearance of the step edge. +2.00DS gave a 61.0 ± 12.7mm mean lead toe clearance compared to 47.5 ± 14.0mm with the control condition and 38 ±12.4mm with -2.00DS (p<0.0001).
CONCLUSIONS: The plus and minus blur lenses had similar effects on visual acuity and stereopsis. However, their effects on stepping strategies were driven by their magnification effect on the position and size of the step. Gait changes indicated that the step appeared further away and shorter with minus lenses or closer and taller with plus lenses. In some cases subjects lost balance or had to use compensatory strategies. The results suggest that falls rate may be increased in new spectacle wearers due to the effects of spectacle magnification. Partial prescribing large refractive changes in older people at risk of falls is highly recommended and all older patients should be appropriately warned of the effects of new spectacles on the apparent position and size of steps and stairs.
|Affiliation of Co-Authors||University of Bradford, Dept. of Optometry|