The ciliary ganglion is a small, flat body lying laterally to the optical nerve in the orbit. Its parasympathetic fibers from the Edinger–Westphal nucleus run in the oculomotor nerve and cross over to the ganglion as oculomotor root (parasympathetic root). The preganglionic sympathetic fibers originate from the lateral horn of the spinal cord C8–T2 (ciliospinal center) and synapse in the superior cervical ganglion. The postganglionic fibers ascend in the carotid plexus as sympathetic root to the ciliary ganglion. Sensory fibers originate from the nasociliary nerve (nasociliary root).
The short ciliary nerves extend from the ganglion to the eyeball and penetrate the sclera to enter the interior of the eyeball. Their parasympathetic fibers innervate the ciliary muscle (accommodation) and the sphincter pupillae muscle; the sympathetic fibers innervate the dilator pupillae muscle.
Clinical Note: The pupil is antagonistically innervated by parasympathetic fibers (constriction of pupil) and sympathetic fibers (dilatation of pupil). Injury to the ciliospinal center or the spinal roots C8, T1 results in ipsilateral constriction of the pupil.