The role of the pupil light reflex in aiding adaptation to the dark

Abstract Various proposals for the function of the pupillary light reflex are discussed in quantitative terms. Two proposals are examined experimentally. It is suggested that the major purpose of pupillary constriction to light is to reduce retinal illumination and prepare the eye for a return to darkness. A mobile pupil (as opposed to a fixed) produces a substantial improvement in stimulus detection during the first few minutes of dark adaptation.