April 2011
Volume 52, Issue 14
ARVO Annual Meeting Abstract  |   April 2011
Relationship Between Vertical Heterophoria and Susceptibility to Motion Sickness
Author Affiliations & Notes
  • Danielle N. Jackson
    Optometry, University of Houston, Houston, Texas
  • Harold E. Bedell
    Optometry, University of Houston, Houston, Texas
  • Footnotes
    Commercial Relationships  Danielle N. Jackson, None; Harold E. Bedell, None
  • Footnotes
    Support  Short-term training grant, T35 EY07088, and core grant, P30 EY07751, from the National Eye Institute.
Investigative Ophthalmology & Visual Science April 2011, Vol.52, 4700. doi:
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      Danielle N. Jackson, Harold E. Bedell; Relationship Between Vertical Heterophoria and Susceptibility to Motion Sickness. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4700.

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      © ARVO (1962-2015); The Authors (2016-present)

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Purpose: : Motion sickness is reported to be a common symptom in patients with vertical heterophoria. This study assessed the relationship between vertical phoria and susceptibility to motion sickness in a non-clinical sample of 43 subjects.

Methods: : The vertical phoria of each eye was measured with a Maddox rod after 30 s of occlusion and then averaged. To evaluate susceptibility to motion sickness, subjects read 14-point text for 10 min while sitting inside a 1.45 m optokinetic drum that rotated horizontally at 37 deg/s. Subjects rated their level of motion sickness (0 - 6 scale) at 1 min intervals during drum rotation, and the magnitude of 13 motion-sickness symptoms (0 - 3 scale) after drum rotation ended.

Results: : Vertical phorias ranged from 0 to 2.1 prism diopters (pd), with a median value of 0.4 pd. The magnitude of vertical phoria correlated significantly with both the maximum rating of motion sickness during drum rotation (r = 0.41, p = 0.006) and the summed symptom score following rotation (r = 0.33, p = 0.03). A vertical phoria of 0.75 pd discriminated best between subjects with low vs. high summed motion-sickness-symptom scores (t = 4.8, p < 0.0001). Neither the subjects’ age or gender was related to the magnitude of vertical phoria or to motion-sickness scores. To assess whether image misalignment per se affects susceptibility to motion sickness, in 12 subjects with small vertical phorias (mean = 0.2 pd) a vertical prism (average = 2 pd) was introduced to increase artificially the magnitude of phoria. Only one subject exhibited a substantial increase in motion-sickness symptoms during prism wear.

Conclusions: : Subjects with a vertical phoria greater than or equal to 0.75 pd exhibit an increased susceptibility to motion sickness. In subjects with a vertical phoria less than 0.75 pd, artificially increasing the phoria usually does not increase motion-sickness scores, suggesting the relationship between vertical image misalignment and motion sickness may not be causal. Susceptibility to motion sickness in subjects large and small vertical phorias may be attributable to different physiological mechanisms.

Keywords: vergence • eye movements 

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