pupillary reflex An alteration in the size of the pupil in response to a change in the light intensity. An increase in light intensity causes both pupils to contract (see iris) even if only one retina is directly stimulated. This is known as a consensual reflex. Conversely, a decrease in light intensity causes dilation of the pupils.

pupillary reflex (light reflex) n. the reflex change in the size of the pupil according to the amount of light entering the eye.