[4] It contains parasympathetic pre-ganglionic neuron cell bodies that synapse in the ciliary ganglion.

[3][2] It contributes the autonomic, parasympathetic component to the oculomotor nerve (CN III),[4] ultimately providing innervation to the iris sphincter muscle and ciliary muscle to mediate the pupillary light reflex and accommodation, respectively.

[6] The paired nuclei are posterior to the main motor nucleus (oculomotor nucleus) and anterolateral to the cerebral aqueduct in the rostral midbrain at the level of the superior colliculus.

[10] The EWN receives feedback from the locus coeruleus about illumination of the retina in order for the EWN to adjust the size of the pupil in response to varying ambient brightness.

It has also been implicated in the mirroring of pupil size in sad facial expressions.