Korean J Aerosp Environ Med.  2007 Dec;17(3):113-117.

Effect of Acute Hypobaric Hypoxia on Binocular Fusionin Subjects Having Heterophorias

Affiliations
  • 1Aero Space Medical Center, Cheongwon, Korea. sejoon1@daum.net
  • 2Department of Ophthalomology, Seoul National University Hospital, Seoul, Korea.
  • 3Department of Internal Medicine, Seoul National University Hospital, Seoul, Korea.
  • 4Department of Ophthalmology, Seoul National University Bundang Hospital, Seongnam, Korea.

Abstract

BACKGROUND: Heterophoria has been considered a disqualifying condition to flying performance because heterophoria, when exposed to high altitude hypoxia, becomes heterotropia causing double vision. However, there has been no actual evidence supporting this assumption. We investigated the binocular fusional ability and symptoms in the subjects having heterophorias upon exposure to acute hypobaric hypoxia.
METHODS
15 subjects having heterophorias and 7 normal controls were included. All the subjects had exophoria and 1 subject had exophoria and hyperphoria. High altitude hypobaric hypoxic condition was simulated in a decompression chamber. Using Worth 4 dot test we measured the binocular fusional ability. To analyze the quality of binocular vision, we measured the stereoscopic visual acuity. By comparing the data between subjects and controls, we evaluated the binocular vision and fusional ability of subjects having heterophorias.
RESULTS
All the subjects and controls showed no disruption of binocular fusion on Worth 4 dot test upon exposure to hypoxia. On the whole, 7 of 15 subjects and 3 of 7 controls showed decreased level of stereopsis without significant differences between the two groups. There were no differences in binocular vision including fusional ability and stereopsis between the subjects and the controls in acute hypoxic condition.
CONCLUSION
The subjects with heterophorias had stable binocular fusional ability resistant to acute hypobaric hypoxia, which showed no difference from the normal controls. Conclusively, we could not find any disadvantage in heterophoric persons with regard to flying performance. Visual standards for aviation personnel regarding heterophorias also need to be more lenient.

Keyword

Heterophoria; Hypoxia; Aviation; Fusion; Diplopia

MeSH Terms

Altitude
Anoxia*
Aviation
Decompression
Depth Perception
Diplopia
Diptera
Exotropia
Humans
Telescopes*
Vision, Binocular
Visual Acuity
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