Abstract

Dark-adaptation curves were obtained from three observers: one was tested 15 times, the others 24 times each. Half of the tests were taken immediately upon entering the darkroom, the other half after 30 minutes rest in total darkness. The variability of threshold measurements is approximately twice as large in the former as in the latter condition. It appears that exposure to light prior to the standard procedure of testing exerts an influence upon subsequent threshold measurements, unless the visual receptor system is allowed to reach a state of equilibrium before the standard pre-exposure is given. This assumption is supported by experiments in which two observers spent half an hour reading under bright outdoor skylight. When the eyes are not shielded from high luminances, or when luminance is only slightly reduced, the delayed dark adaptation curves reach lower levels than when the tests are made immediately. However, when the eyes are shielded by dense goggles dark-adaptation curves obtained in immediate and delayed tests are indistinguishable. It seems probable, therefore, that variability in dark adaptation is at least in part a function of residual effects of exposure to light antecedent to routine pre-exposure and threshold measurements in dark-adaptation tests.

© 1960 Optical Society of America

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