Color Vision in the Mountains.

This Lessons from History article uses science, aviation, medicine, and mountaineering sources to describe some of the effects of hypoxia, illumination, and other environmental conditions on the eye, the central nervous system, and light and color perception. The historical perspective is augmented by an analysis of an informal observation of the altered perception of red color on a deck of playing cards while climbing Mera Peak in the Himalaya. The appearance of a grayer red color on the cards was initially attributed to the effects of hypoxia alone. Instead, analysis of cards in combination with the low incidence of protan color vision defects at altitude indicated that glare and contrast effects in the extremely bright lighting environment combined with hypoxia likely caused the perception of a grayer red. The incident provides an educational opportunity for review, analysis, and commentary about some of the complex elements that impact color vision.