title: Effects of gaze strategy on standing postural stability in older multifocal wearers.
abstract: BACKGROUND
  Postural instability in older people is associated with an increased risk of falling. This experiment investigated the effects of different gaze strategies on postural stability in older people, when using distance single-vision compared with multifocal (progressive addition lens and bifocal) spectacles.
  
  
  METHODS
  Eighteen healthy older habitual multifocal spectacle-wearers (mean age 72.1 +/- 4.0 years) participated in a randomised, cross-over study. Postural stability during quiet standing was assessed as the root mean square excursion in the centre of pressure (RMS-COP) in the antero-posterior direction. Ground reaction force data were collected (for 30 seconds), while subjects viewed one of two visual targets (one square metre) of different spatial frequencies and contrasts, while wearing either distance single-vision or multifocal (progressive addition and bifocal) spectacles. The visual targets were positioned either ahead at eye-level or on the ground (viewing distance 2.06 metres) and viewed under the following head-gaze conditions; 'head neutral-gaze forward', 'head flexed-gaze down' and 'head neutral-gaze down'.
  
  
  RESULTS
  The type of spectacles worn or the target viewed had no significant effect on postural stability but postural stability deteriorated (antero-posterior RMS-COP excursion increased) in the 'head neutral-gaze down' compared with the 'head flexed-gaze down' and 'head neutral-gaze forward' conditions (5.9, 5.5 and 5.0 mm respectively, p < 0.001).
  
  
  CONCLUSIONS
  Multifocal use had no effect on standing postural stability. Irrespective of spectacles worn, when fixating a visual target positioned at ground level, postural stability was better in the 'head flexed-gaze down' condition compared with the 'head neutral-gaze down' condition. A useful strategy to reduce falling in the older person might be to advise multifocal and distance single-vision spectacle-wearers to flex their heads rather than just lower their eyes when looking downwards.
authors.affiliation: Department of Optometry, University of Bradford, Bradford, West Yorkshire, United Kingdom. l.johnson4@bradford.ac.uk
authors.forename: Louise
authors.initials: L
authors.lastname: Johnson
authors.forename: David B
authors.initials: DB
authors.lastname: Elliott
authors.forename: John G
authors.initials: JG
authors.lastname: Buckley
mesh_terms: D000058:Accidental Falls; D000368:Aged; D015350:Contrast Sensitivity / Q000502:physiology; D018592:Cross-Over Studies; D003867:Depth Perception / Q000502:physiology; D005133:Eye Movements / Q000502:physiology; D005139:Eyeglasses / Q000009:adverse effects*; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010775:Photic Stimulation; D004856:Postural Balance / Q000502:physiology; D011187:Posture / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology*; D014792:Visual Acuity / Q000502:physiology