title: Head-Eye Coordination Increases with Age and Varies across Countries.
abstract: OBJECTIVE
  Head movements in older people may contribute to their dizziness and equilibrium problems. Head gain is the ratio of head movement to total movement (head + eye) when executing a saccade to an eccentric target. Two studies have investigated the relationship between head gain and age but have provided conflicting results.
  
  
  METHODS
  We report head gain data collected from research laboratories and optician stores. Our sample sizes are much larger (n = 657 for laboratory, n = 64,458 for optician stores), permitting more detailed analyses.
  
  
  RESULTS
  The head-eye coefficient, expressed as 100 times the square root of head gain, was bimodal with one mode of primarily eye movers and one mode of eye-and-head movers. Head-eye coefficient increased with age and was invariant with eye correction and gender. We also found an effect of nation that seemed associated with gross domestic product or by latitude (in the northern hemisphere) and log population density.
  
  
  CONCLUSIONS
  Assuming that head movements and visual distortions contribute to dizziness and equilibrium problems, our study suggests that customizing eyewear based on age and country may help in reducing the prevalence of problems associated with head and/or eye movements.
authors.affiliation: *PhD Université de Montréal, Ecole d'Optometrie, Montréal, Québec, Canada (all authors); and Essilor Canada, Montréal, Québec, Canada (GG).
authors.forename: Frédéric J A M
authors.initials: FJ
authors.lastname: Poirier
authors.forename: Guillaume
authors.initials: G
authors.lastname: Giraudet
authors.forename: Jocelyn
authors.initials: J
authors.lastname: Faubert
mesh_terms: D000328:Adult; D000375:Aging / Q000502:physiology*; D005006:Ethnicity; D005133:Eye Movements / Q000502:physiology*; D005260:Female; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011597:Psychomotor Performance / Q000502:physiology*; D012438:Saccades / Q000502:physiology