Ciliary ganglion

Where is the ciliary ganglion located?

The ganglion is located within the adipose tissue of the orbital cavity. Anatomically, it lies closely apposed to the lateral aspect of the optic nerve (n. opticus, cranial nerve II).

Which roots form the ganglion?

Three types of nerve fibers converge on the ciliary ganglion to form its roots:

• Parasympathetic root (radix oculomotoria): formed by preganglionic fibers branching off the inferior division of the oculomotor nerve (n. oculomotorius). These fibers originate in the midbrain from the accessory parasympathetic nucleus (Edinger-Westphal nucleus) and form synaptic contacts directly with the cells of the ciliary ganglion.
• Sensory root (radix nasociliaris): a branch of the nasociliary nerve (derived from the ophthalmic nerve, V1 division of the trigeminal nerve).
• Sympathetic root (radix sympathica): a branch originating from the autonomic plexus of the ophthalmic artery (contains postganglionic fibers).

What do the branches of the ganglion innervate?

Postganglionic fibers—the short ciliary nerves (nn. ciliares breves)—arise from the cells of the ciliary ganglion. Together with the long ciliary nerves, they pierce the eyeball and form the ciliary plexus within the substance of the ciliary muscle, with branches extending to the ciliary body and iris.

The short ciliary nerves innervate the intrinsic eye muscles:

• Sphincter pupillae muscle (m. sphincter pupillae): its fibers are arranged circularly at the pupillary margin of the iris. Contraction causes miosis (pupillary constriction).
• Ciliary muscle (m. ciliaris): responsible for the act of accommodation.

How does the ganglion participate in physiological processes?

Pupillary light reflex The ciliary ganglion forms part of the efferent (motor) limb of the reflex arc. A light stimulus from the retina travels along visual pathways to the pretectal nucleus (nucleus pretectalis), from which interneurons bilaterally transmit the signal to the Edinger-Westphal parasympathetic nuclei. From there, preganglionic fibers travel to the ganglion ciliare, where synaptic relay occurs. Postganglionic fibers stimulate contraction of the pupillary sphincter. Due to bilateral connections in the brain, the pupillary response is both direct (in the illuminated eye) and consensual (in the unilluminated eye).

Mechanism of accommodation When viewing near objects, parasympathetic impulses stimulate contraction of the ciliary muscle. The muscular ring constricts and moves forward, slackening the tension on the suspensory ligaments of the lens (zonule of Zinn). Owing to its inherent elasticity, the lens assumes a more convex shape, increasing the refractive power of the eye to focus on a near object.

Clinical significance and pathologies

• Efferent pathway lesion: Damage to the oculomotor nerve or the ciliary ganglion itself interrupts the conduction of nerve impulses to the pupillary sphincter. Clinically, this manifests as an absence of pupillary constriction on the affected side (ipsilaterally).
• Adie's syndrome (idiopathic): A condition associated with idiopathic (typically congenital) degeneration of the ciliary ganglion and postganglionic parasympathetic fibers. It is characterized by unilateral mydriasis (pupillary dilation) and tonic pupil (pupillotonia)—a slow, tonic constriction and dilation of the pupil upon testing the light reflex.

Class and exam questions

What else to study on this topic

• Oculomotor nerve (n. oculomotorius)
• Pupillary light reflex
• Autonomic nervous system: parasympathetic division
• Anatomy of the eyeball

Other topics in the "Anatomical Structures" section

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