Visual function at altitude under night vision assisted conditions.
BACKGROUND
Hypoxia, even mild, is known to produce negative effects on visual function, including decreased visual acuity and sensitivity to contrast, mostly in low light. This is of special concern when night vision devices (NVDs) are used during flight because they also provide poor images in terms of resolution and contrast.


METHODS
While wearing NVDs in low light conditions, 16 healthy male aviators were exposed to a simulated altitude of 12,500 ft in a hypobaric chamber.


RESULTS
Snellen visual acuity decreased in normal light from 28.5 +/- 4.2/20 (normoxia) to 37.2 +/- 7.4/20 (hypoxia) and, in low light, from 33.8 +/- 6.1/20 (normoxia) to 42.2 +/- 8.4/20 (hypoxia), both at a significant level. An association was found between blood oxygen saturation and visual acuity without significance. No changes occurred in terms of sensitivity to contrast.


CONCLUSIONS
Our data demonstrate that mild hypoxia is capable of affecting visual acuity and the photopic/high mesopic range of NVD-aided vision. This may be due to several reasons, including the sensitivity to hypoxia of photoreceptors and other retinal cells. Contrast sensitivity is possibly preserved under NVD-aided vision due to its dependency on the goggles' gain.
Aerospace Medicine Department, Experimental Flight Centre, Italian Air Force Logistic Command, Aeroporto di Pratica di Mare, Pomezia, Italy.
Diego
D
Vecchi
Aerospace Medicine Department, Experimental Flight Centre, Italian Air Force Logistic Command, Aeroporto di Pratica di Mare, Pomezia, Italy.
Fabio
F
Morgagni
Aerospace Medicine Department, Experimental Flight Centre, Italian Air Force Logistic Command, Aeroporto di Pratica di Mare, Pomezia, Italy.
Anton G
AG
Guadagno
Aerospace Medicine Department, Experimental Flight Centre, Italian Air Force Logistic Command, Aeroporto di Pratica di Mare, Pomezia, Italy.
Marco
M
Lucertini
D000328:Adult; D000337:Aerospace Medicine; D000531:Altitude; D015350:Contrast Sensitivity; D003623:Dark Adaptation; D005139:Eyeglasses; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D055254:Night Vision; D014787:Vision Tests; D014785:Vision, Ocular; D014792:Visual Acuity