title: Multifocal spectacles increase variability in toe clearance and risk of tripping in the elderly.
abstract: OBJECTIVE
  Epidemiologic studies have indicated that elderly people who wear multifocal spectacles have an increased risk of tripping, particularly on stairs. Yet no studies have experimentally examined how wearing multifocal spectacles affects stair and step negotiation. The purpose of this study was to determine the effects of wearing multifocal compared with single-distance vision spectacles on minimum toe clearance and risk of tripping during step negotiation in the elderly.
  
  
  METHODS
  Nineteen healthy subjects (mean age, 71.4 years) performed a single step up to a new level (heights, 7.5, 15, and 22 cm) while wearing multifocal (bifocals and progressive addition lenses) or single-distance vision spectacles. Minimum horizontal and vertical toe clearance were assessed by analyzing data collected with a five-camera, three-dimensional motion-analysis system.
  
  
  RESULTS
  There was no difference in mean minimum toe clearance in subjects when wearing multifocal compared with single-distance vision spectacles. However, there was greater within-subject variability in vertical toe clearance when wearing multifocal spectacles (variance ratio, 1.53; P = 0.0004). Subjects were also significantly more likely to trip when wearing multifocal compared with single-vision spectacles (one-sided Fisher's exact test P = 0.025).
  
  
  CONCLUSIONS
  Because of increased within-subject variability in vertical toe clearance when wearing multifocal spectacles, elderly individuals may be at greater risk of falling when negotiating steps and stairs if they do not also consistently increase margins of safety (mean vertical toe clearance). This suggests that some elderly who are at high risk of falling may benefit from wearing single-distance vision rather than multifocal spectacles when walking.
authors: Vision and Mobility Research Laboratory, Department of Optometry, School of Health Studies, University of Bradford, Bradford, West Yorkshire, UK.
authors: Louise
authors: L
authors: Johnson
authors: John G
authors: JG
authors: Buckley
authors: Andy J
authors: AJ
authors: Scally
authors: David B
authors: DB
authors: Elliott
mesh_terms: D000058:Accidental Falls; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology; D015350:Contrast Sensitivity / Q000502:physiology; D003867:Depth Perception / Q000502:physiology; D005139:Eyeglasses / Q000009:adverse effects*; D005260:Female; D005684:Gait / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D004856:Postural Balance / Q000502:physiology; D012030:Refractive Errors / Q000628:therapy; D012307:Risk Factors; D014034:Toes / Q000502:physiology*; D016138:Walking / Q000502:physiology