Abstract

Dark adaptation curves are obtained by presenting a 2° square testfield 6° below the center of the fovea for both eyes tested separately and for both eyes tested alternately. When the pre-exposure luminances for the two eyes differ, the independently recorded dark adaptation curves for the two eyes show differences in correspondence with the difference in radiant energy delivered to the eyes during pre-exposure. However, if both eyes are pre-exposed simultaneously to their respective luminances, and are alternately tested, the dark adaptation curves are not identical with those previously found. They move closer together, or coincide, i.e., the differences in threshold sensitivity become smaller, or disappear. When pre-exposure of the two eyes differs merely in admitting the near ultraviolet (285–400 mμ) to one eye, and screening it from the other, the curves independently recorded for the two eyes have different threshold levels, but in alternate testing no difference is found. It is also shown that an influence of the near ultraviolet upon visual thresholds is readily found when white and blue testlights are employed; it is barely evident when a green testlight is used and is not found with a red testlight.

© 1955 Optical Society of America

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