Abstract
Purpose: :
Hypoxia is known to alter a number of CNS functions including visual functions. In this study, we investigated changes in color discrimination for tritan, deutan and protan axes as a result of extreme natural hypobaric hypoxia at different altitudes during a medical research expedition into the 'death zone' (above 8000 m) on Mt. Everest 8850m, Nepal.
Methods: :
The Mt. Everest hypoxia research expedition in May 2008 consisted of two members (ages 31 and 46 yrs). The subjects were tested for color vision discrimination along the tritan/deutan and protan axes in color space using the Cambridge Colour Test (Cambridge Research Systems, Cambridge, UK) over a period of 50 days at various altitudes. The stimuli were presented on a calibrated LCD screen (Asus Eee) at 8 degrees of visual angle in a dark tent 4 hours after sunset. The measurments were taken at heights of 3450m, 4410m, 4820m post 5300m, 5300m, 6470m, 7100m and 6470m post 8400m. Control measurements were taken 4 weeks and 6 months after the expedition at 50m.
Results: :
Complete data records of two participants (4 eyes) were analyzed. In both mountaineers a consistent and significant rise of the tritan color discrimination threshold with increased altitude exposure was observed. However, deutan and protan thresholds remained within normal limits.
Conclusions: :
We investigated the effects of extreme natural hypobaric hypoxia on color discrimination over a 50-day period using a psychophysical vision test. We conclude, that hypobaric hypoxia results in a decrease in color discrimination along the tritan (blue/yellow) axis with increasing altitude. No impairments were noted in the red and green ranges.
Keywords: color vision • hypoxia • ischemia