Absolute and Differential Light Sensitivity of the Dark-adapting Eye

Abstract

THE lack of correlation between the absolute light threshold of the dark-adapted eye and the 'ability to see in the dark' has been currently attributed to psychological factors; but little attention has been given to the behaviour of contrast sensitivity, despite the fact that vision at low illumination depends largely on the perception of differences in brightness. In particular, the possibility of variations in contrast sensitivity independent of variations in the absolute threshold does not seem to have been investigated, although the occurrence of such variations seems likely from the observations of Edmund and others^1,2.