Vertical heterophoria and susceptibility to visually induced motion sickness

Strabismus. 2012 Mar;20(1):17-23. doi: 10.3109/09273972.2011.650813.


Motion sickness is reported to be a common symptom in patients with vertical heterophoria. The goal of this study was to assess the relationship between vertical phoria and susceptibility to motion sickness in a nonclinical sample of 43 subjects. Vertical phoria was measured with a Maddox rod after 30 s of occlusion. To evaluate susceptibility to motion sickness, subjects read text while sitting inside a rotating optokinetic drum for 10 min. Subjects rated their level of motion sickness at 1 min intervals during drum rotation and the magnitude of 13 motion sickness symptoms after drum rotation ended. The magnitude of vertical phoria ranged from 0 to 2.13 prism diopters (pd) with a mean of 0.46 pd and correlated significantly with both the maximum rating of motion sickness during drum rotation and the summed symptom score following rotation. A vertical phoria of 0.75 pd discriminated best between subjects with low vs high summed motion sickness symptom scores (p < 0.0001). Introducing a prism to artificially increase the phoria of 12 subjects with vertical phorias <0.75 pd increased motion sickness symptoms in only 1 subject. Prisms that reduced the phoria of subjects with vertical phorias > 0.75 pd reduced motion sickness symptoms in 2 of the 4 subjects tested. The results confirm an association between vertical phoria and motion sickness, but suggest the relationship may not be causal.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adult
  • Disease Susceptibility
  • Female
  • Humans
  • Male
  • Middle Aged
  • Motion Perception / physiology
  • Motion Sickness / diagnosis
  • Motion Sickness / physiopathology*
  • Nystagmus, Optokinetic / physiology
  • Strabismus / diagnosis
  • Strabismus / physiopathology*
  • Young Adult