Short-term hypobaric hypoxia enhances visual contrast sensitivity.

The effect of hypoxia on early visual functions remains a controversial area of research. To explore this question, we measured static and dynamic visual contrast sensitivity in 14 healthy volunteers at a simulated altitude of 5500 m. In comparison with the baseline condition (mean arterial oxygen saturation: 98.4%), contrast sensitivity significantly increased after 5, 10 and 15 min of hypoxic exposure (saturation: 82.9%, 77.0%, 74.3%, respectively). After 10 min, this enhancement was markedly pronounced under dynamic conditions. Returning to the baseline altitude (saturation: 97.7%), contrast sensitivity recovered, mostly at the lower spatial frequencies. There was a significant negative relationship between arterial oxygen saturation and contrast sensitivity values at low and medium spatial frequencies (0.5-4.8 c/deg). These results suggest that early visual processing may be enhanced during short-term hypoxic challenge.