title: Negligible impact on posture from 5-diopter vertical yoked prisms.
abstract: OBJECTIVE
  Yoked prisms are used by some optometrists to adjust posture, but evidence to support this practice is sparse and low level. The aim of this research was to investigate whether vertical yoked prisms have an impact on posture in healthy adults.
  
  
  METHODS
  Posture was assessed objectively in 20 healthy adults, by recording a range of joint angles or body segment locations at the ankle, hip, torso, neck, and head during participant observation of a straight-ahead target, and subsequently with eyes closed. Recording occurred before, during, and after wearing goggles with control plano lenses, and 5-diopter (D) base-up and 5-D base-down yoked prisms. In each viewing condition, the goggles were worn for 30 minutes. Interaction effects of lens/prism condition by time on joint angles and body orientation were determined.
  
  
  RESULTS
  In the eyes-open and eyes-closed conditions, no significant lens/prism × time interaction effects were found at the torso, neck, hip, or ankle (P > 0.1). However, in both eyes-open and eyes-closed conditions a significant lens/prism × time interaction was found at the head (P = 0.031 and 0.006, respectively), with head extended (tilted backward) by up to 2.5 degrees more while viewing with base-down prisms than with plano lenses.
  
  
  CONCLUSIONS
  In healthy adults, 5-D base-down yoked prisms were not associated with a change in body posture. A small effect on head orientation and not at other locations suggests a minimal effect on posture. Research in a larger sample and in individuals with abnormal posture is needed to verify this.
authors.affiliation: School of Optometry and Vision Science UNSW, Sydney, Australia 2Optometry and Visual Science, School of Health Sciences, City University London, London, United Kingdom.
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Suttle
authors.affiliation: School of Optometry and Vision Science UNSW, Sydney, Australia.
authors.forename: Lisa J
authors.initials: LJ
authors.lastname: Asper
authors.affiliation: Neuroscience Research Australia, Randwick, Australia.
authors.forename: Daina
authors.initials: D
authors.lastname: Sturnieks
authors.affiliation: Neuroscience Research Australia, Randwick, Australia.
authors.forename: Jasmine
authors.initials: J
authors.lastname: Menant
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D005139:Eyeglasses; D005260:Female; D006257:Head / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011187:Posture / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology; D055815:Young Adult