Hypoxia, color vision deficiencies, and blood oxygen saturation.

Chromatic thresholds were measured using the Cambridge Colour Test (CCT), the Colour Assessment and Diagnosis (CAD) test, and the Cone Specific Contrast Test (CSCT) at ground and 3780 m (12,400 ft) for subjects with normal color vision and red-green color vision defects. The CAD revealed a small (~10%) increase in the red-green thresholds for the trichromatic subjects and a similar increase in the blue-yellow thresholds for the dichromats. The other two color vision tests did not reveal any significant change in chromatic thresholds. The CAD results for the trichromats were consistent with a rotation of the discrimination ellipse counterclockwise with little change in the elliptical area. This alteration in the color discrimination ellipse can occur when retinal illumination is lowered.