title: Vertical heterophoria and susceptibility to visually induced motion sickness.
abstract: 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.
authors.affiliation: College of Optometry, University of Houston, TX 77204-2020, USA.
authors.forename: Danielle N
authors.initials: DN
authors.lastname: Jackson
authors.forename: Harold E
authors.initials: HE
authors.lastname: Bedell
mesh_terms: D000328:Adult; D004198:Disease Susceptibility; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009039:Motion Perception / Q000502:physiology; D009041:Motion Sickness / Q000175:diagnosis / Q000503:physiopathology*; D017120:Nystagmus, Optokinetic / Q000502:physiology; D013285:Strabismus / Q000175:diagnosis / Q000503:physiopathology*; D055815:Young Adult