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Abstract
The effect of the inspiration of a mixture of 10 per cent oxygen and 90 per cent nitrogen on several aspects of dark adaptation was studied in three highly trained observers. Arterial oxygen saturations were monitored during all experiments. The necessity of using highly trained subjects and particidarly of monitoring arterial oxygen saturations in such studies was emphasized. Hyperventilation effects, seen initially in all subjects, were eliminated by training. Such effects, as well as other possible changes in oxygen saturation, may be missed unless careful monitoring is done. Hypoxia raised both cone and rod absolute visual thresholds. However, cone thresholds were elevated to a greater degree than rod thresholds at a 5° retinal eccentricity where both were studied. Hypoxia had a greater effect on peripheral rod thresholds (measured at 45° eccentricity) than on central rod thresholds (measured at 45° eccentricity). Only the later portions of rod and cone dark adaptation curves xoere affected by hypoxia. The first four minutes of either type of curve toas unaffected.