The nerve also contains fibers that innervate the intrinsic eye muscles that enable pupillary constriction and accommodation (ability to focus on near objects as in reading).

The fibers from the two third nerve nuclei located laterally on either side of the cerebral aqueduct then pass through the red nucleus.

From the red nucleus fibers then pass via the substantia nigra[citation needed] to emerge from the substance of the brainstem at the oculomotor sulcus (a groove on the lateral wall of the interpeduncular fossa).

[2] On emerging from the brainstem, the nerve is invested with a sheath of pia mater, and enclosed in a prolongation from the arachnoid.

The oculomotor nerve (CN III) arises from the anterior aspect of the mesencephalon (midbrain).

The nerve also includes axons of type GVE, general visceral efferent, which provide preganglionic parasympathetics to the ciliary ganglion.

Loss of accommodation and continued pupillary dilation can indicate the presence of a lesion on the oculomotor nerve.