What is the expected reaction of the pupil of one eye when light is directed into the pupil of the other eye?

When light is directed into one pupil, the expected reaction is for the pupil of the other eye to constrict as well. This phenomenon is known as the consensual reflex. The consensual reflex occurs because both pupils are controlled by the same neurological pathways. When light stimulates the retina of one eye, signals are sent to the midbrain, which then affects both pupils to constrict, even if the light is only directed at one eye.

This response helps to protect the retina from excessive light exposure and enhances the depth of focus for clear vision. The neural connections involved in this reflex ensure that both pupils respond similarly for better visual function under varying light conditions. Thus, when assessing pupillary reaction, observing the consensual constriction in the opposite eye indicates proper neurological function.