Changes in the fundus of the eye were studied in 15 members of a mountaineering expedition to Dhaulagiri, Nepal (elevation, 8,167 meters [26,795 ft]). Retinal photographs were taken at sea level and at 5,883 meters (19,300) after each climber had descended from his highest point. Five Nepali Sherpas and an additional American climber who came to the base camp late in the climb were also studied.
Vascular engorgement with tortuosity, a 24% increase in arterial diameter, and a 23% increase in venous diameter were observed. Retinal hemorrhages were seen in five American climbers (33%), but in none of the Sherpas. The high incidence is striking, but the cause is unknown. We suggest that the hypoxic vasodilatation makes retinal vessels more vulnerable to sudden rises in intravascular pressure.
Rennie D, Morrissey J. Retinal Changes in Himalayan Climbers. Arch Ophthalmol. 1975;93(6):395-400. doi:10.1001/archopht.1975.01010020409001