Color vision in the tritan axis is predominantly affected at high altitude.

The purpose of this study was to evaluate color vision during high altitude mountain climbing by applying the Mollon-Reffin Minimalist test to 14 climbers, all of whom were participating in the expedition to Ama Dablam (6,812 m) in Nepal. Before leaving for Nepal (at 300 m), all 28 eyes showed normal color vision in all 3 axes. At 1,300 m, 100% of eyes showed normal color vision in the protan and deutan axes, while 25% showed minimally reduced color discrimination in the tritan axis. At 4,000 m, 100% showed normal deutan axis, 4% minimally reduced protan axis, and 72% minimally reduced tritan axis discrimination. At 5,400 m 100% of eyes tested showed normal protan and deutan axis discrimination, while 75% showed minimally and 25% moderately reduced tritan axis discrimination. Back home at 300 m 3 days after return, 100% showed normal deutan, 4% minimally reduced protan, and 38% minimally reduced tritan axis discrimination. One year later, all eyes showed normal color vision in all three axes. Changes in tritan axis discrimination correlated well with increased heart rate (r = 0.69; p = 0.0001) and decreased oxygen saturation (r = 0.71; p = 0.001) at high altitude. This study shows that the tritan color vision axis is predominantly affected at high altitude, but that this reduced color discrimination is transient.