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Depth perception after prolonged usage of night vision goggles
1Air Vehicles and Crew Systems Technology Department, Naval Air Development Center, Warminster, PA 18974-5000.
Aviation, Space, and Environmental Medicine
|June 1, 1989
Summary
Night vision goggle use during helicopter flights may cause temporary eye muscle imbalance (exophoric shift), potentially affecting stereoscopic depth perception. This shift, not a loss of contrast sensitivity, may explain reported depth perception failures.
Area of Science:
- Aviation ophthalmology
- Human factors in aviation
Background:
- Reports of helicopter pilot failures in stereoscopic depth perception tests after night vision goggle (NVG) use.
- NVGs are crucial for night operations but may impact visual function.
Purpose of the Study:
- Investigate the cause of reported depth perception deficits in helicopter pilots after NVG use.
- Assess changes in visual parameters including depth perception, phoria, and contrast sensitivity.
Main Methods:
- 12 helicopter pilots/copilots underwent pre- and post-flight assessments.
- Evaluated parameters included depth perception, lateral/vertical phoria, and contrast sensitivity.
- Pilots wore either PVS-5A or AN/AVS-6 NVGs for 1-4 hour missions.
Main Results:
- Contrast sensitivity and monocular-cued depth perception remained stable.
- An average exophoric shift of 1.5 prism diopters in lateral phoria was observed in 12 of 24 missions.
- No significant changes in vertical phoria or contrast sensitivity were noted.
Conclusions:
- The observed exophoric shift in lateral phoria may explain the reported failures in stereoscopic depth perception tests.
- Increased fusional effort due to vergence accommodation might degrade minimum resolvable disparity.
- Further research into phoria shifts and their implications for aviator performance is warranted.