During sleep the pupils are partially constricted but still react to light. The pathway begins in the cortex, which exerts a modulatory effect on constriction which is lost during drowsiness and sleep but increased during intense concentration and arousal. Pupillary dilatation is controlled by the sympathetic system and is efferent only. Short ciliary nerves then innervate the iris sphincter and muscles of accommodation. They travel in the superficial part of the oculomotor nerve via the cavernous sinus and the superior orbital fissure to synapse in the ciliary ganglia. From each Edinger-Westphal nucleus, preganglionic parasympathetic fibres exit with the oculomotor nerve. Each pretectal nucleus has two pupillary motor outputs, one to the Edinger-Westphal nucleus on its own side and one to the other side.

The efferent limb for pupillary constriction comes from the pretectal nucleus via the Edinger-Westphal nucleus (also in the midbrain) to the ciliary sphincter muscle of the iris. The afferent limb is made up of the retina, the optic nerve and the pretectal nucleus in the midbrain, all on the same side. The pathway for pupillary constriction for each eye has an afferent limb taking sensory information to the midbrain, and two efferent limbs (one to each eye).

Constricted eye pupils