ALTERATIONS IN DARK ADAPTATION UNDER REDUCED OXYGEN TENSIONS

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Abstract
The dark adaptation of 20 human subjects was measured in a low 02 chamber where the partial pressure of O2 could be reduced by dilution with N. The effect of O2 deprivation on light sensitivity was followed for 20 mins. after a 3 min. exposure to a light of 100 millilamberts. Each subject was tested at a simulated altitude of 7,400 feet (15.8% O2), 11,000 feet (13.7% 02) and 15,000 feet (11.7% O2). The CO2 was kept below 0.6%. The dark adaptation curves (plotting threshold against time) were progressively elevated with increasing O2 deprivation. These effects were counteracted within 2 to 3 mins. by inhaling O2. The diminution in light sensitivity was statistically significant for all but 5 of the 18 subjects at the first simulated altitude of 7,400 feet, for all but 1 at 11,000 feet, and for the entire group at 15,000 feet. The changes are not concerned with the photochemical substances of the retina but with the neural elements of both the retina and the central nervous system.

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