Autonomic Innervation of the Eye

Some of the filaments passing through the superior orbital fissure form the sympathetic root of the ciliary ganglion; their contained fibers pass through it without relaying to become incorporated in the 8 to 10 short ciliary nerves. Other filaments join the ophthalmic nerve or its nasociliary branch and reach the eye in the two to three long ciliary nerves that supply the radial musculature in the iris (dilator pupillae). Both long and short ciliary nerves also contain afferent fibers from the cornea, iris, and choroid. Fibers conveyed in the short ciliary nerves pass through a communicating ramus from the ciliary ganglion to the nasociliary nerve; this ramus is called the sensory root of the ciliary ganglion. The parent cells of these sensory fibers are located in the trigeminal (semilunar) ganglion, and their central processes end in the sensory trigeminal nuclei in the brainstem. The sensory trigeminal nuclei have multiple interconnections with other somatic and autonomic centers and thus influence many reflex reactions. Other sympathetic fibers from the internal carotid plexus reach the eye through the ophthalmic periarterial plexus and along its subsidiary plexuses around the central retinal, ciliary, scleral, and conjunctival arteries.

Parasympathetic Fibers. The parasympathetic preganglionic fibers for the eye are the axons of cells in the accessory, or autonomic, (Edinger-Westphal) oculomotor nucleus. They run in the third cranial nerve and exit in the motor root of the ciliary ganglion, where they relay. The axons of these ganglionic cells are postganglionic parasympathetic fibers, which reach the eye in the short ciliary nerves and are distributed to the constrictor fibers of the iris (sphincter pupillae), to the ciliary muscle, and to the blood vessels in the coats of the eyeball.

Neurologic Disorders. Disruption of the sympathetic innervation to the eye at any level along the sympathetic pathways will result in a Horner syndrome, in which the pupil on the involved side is smaller and dilates poorly, especially notable in the dark, and the upper lid droops slightly (ptosis). Depending on where the sympathetic chain is disrupted, there may also be loss of sweating on the ipsilateral face. A lesion of the ciliary ganglion will cause disruption of the parasympathetic fibers to the pupillary constrictor muscle, and there will be isolated enlargement of the ipsilateral pupil, especially notable in lighted conditions, but no findings such as ptosis or extraocular muscle weakness to suggest a lesion along the course of the oculomotor nerve.

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