Course and Branches of the Ophthalmic Artery
The ophthalmic artery (a. ophthalmica) has specific topographical relationships with the optic nerve. Upon entering the orbital cavity, it is located strictly inferiorly and laterally to it. Its course then changes: the artery spirals, carefully curving around the optic nerve from its lateral and superior sides.
The artery gives off several important branches within the orbit:
- To the extraocular muscles — to ensure their adequate blood supply.
- Ciliary arteries (aa. ciliares) — these vessels penetrate directly into the eyeball, surrounding the entry point of the optic nerve.
- Additional branches, among which the lacrimal and supraorbital arteries are distinguished.
Features of the Optic Nerve (CN II)
The optic nerve (n. opticus) is not a classical peripheral nerve, which is reflected in its structure. It is covered by direct extensions of the three meninges (dura, arachnoid, and pia mater) that accompany it along its entire length up to the sclera.
In the orbit, the nerve is surrounded on all sides by a layer of adipose tissue through which various vessels and nerves pass. Of particular importance is the perineural adipose tissue adjacent to the superior surface of the optic nerve. It is in this zone that the long ciliary nerves (nn. ciliares longi) run. They are branches of the nasociliary nerve (n. nasociliaris) and are responsible for the sensory innervation of the structures of the eyeball. The ciliary ganglion lies closely attached to the lateral side of the nerve.
Ciliary Ganglion and Its Innervation
The ciliary ganglion (ganglion ciliare) is a key link in the regulation of eye functions, located on the lateral side of the optic nerve. It receives three functionally distinct roots:
- Sensory root (radix nasociliaris) — is a branch of the nasociliary nerve.
- Parasympathetic root (radix oculomotorius) — originates from the oculomotor nerve.
- Sympathetic root (radix sympathicus) — is formed from the branches of the plexus surrounding the ophthalmic artery.
From the ganglion itself, short ciliary nerves (nn. ciliares breves) extend anteriorly. Their main task is the innervation of the intrinsic muscles of the eye. These include the ciliary muscle (m. ciliaris), sphincter pupillae (m. sphincter pupillae), and dilatator pupillae (m. dilatator pupillae). The combined action of these muscles ensures vital physiological functions — adaptation to light levels and visual accommodation.
Briefly: answers to topical questions
What branches does the ophthalmic artery give off?
The ophthalmic artery gives off the following branches:
- Lacrimal artery (a. lacrimalis) — to the lacrimal gland and eyelids.
- Central retinal artery (a. centralis retinae) — supplies the retina.
- Short and long posterior ciliary arteries (aa. ciliares posteriores breves et longae) — to the choroid and ciliary body.
- Muscular branches (aa. musculares) — supply the rectus and oblique muscles of the eye.
- Posterior ethmoidal artery (a. ethmoidalis posterior) — supplies the mucosa of the posterior ethmoidal air cells and the sphenoid sinus.
- Anterior ethmoidal artery (a. ethmoidalis anterior) — into the nasal cavity.
- Supraorbital artery (a. supraorbitalis) — to the forehead.
- Medial palpebral arteries (aa. palpebrales mediales) — along the margins of the eyelids.
- Supratrochlear artery (a. supratrochlearis) — to the medial part of the forehead and upper eyelid.
- Dorsal nasal artery (a. dorsalis nasi) — to the dorsum of the nose.
Through which opening do the optic nerve and ophthalmic artery enter the orbital cavity?
The optic nerve and ophthalmic artery enter the orbital cavity through the optic canal (canalis opticus). Within this bony structure, the ophthalmic artery is located lateral to the optic nerve. After exiting the canal, the artery crosses the nerve, heading towards the medial wall of the orbit, where it subsequently divides into its terminal branches.
From which blood vessel does the ophthalmic artery branch off?
The ophthalmic artery branches off from the internal carotid artery (a. carotis interna). It is the first intracranial branch of this major blood vessel. Subsequently, the ophthalmic artery forms important anastomoses, providing a connection between the internal and external carotid artery systems (e.g., via the dorsal nasal artery and angular artery).
Where does the sympathetic root of the ciliary ganglion originate?
The sympathetic root of the ciliary ganglion (radix sympathicus) originates from the plexus of the ophthalmic artery. This root is one of the three forming the ciliary ganglion (ganglion ciliare), along with the sensory (branch of the nasociliary nerve) and parasympathetic (from the oculomotor nerve) roots. Short ciliary nerves innervating the eye muscles emerge from the ganglion itself.
Which branch of the ophthalmic artery penetrates inside the optic nerve?
The central retinal artery (a. centralis retinae) penetrates inside the optic nerve. It enters the substance of the optic nerve approximately 1 cm before the eyeball. Passing inside the nerve, this artery reaches the optic disc, where it emerges through a depression in its center and supplies the inner layers of the retina.
To memorize the roots of the ciliary ganglion, use the abbreviation SPS (Sensory, Parasympathetic, Sympathetic) — from the nasociliary, oculomotor, and ophthalmic artery plexus, respectively.
Class and exam questions
How is the ophthalmic artery positioned relative to the optic nerve?
Upon entering the orbit, it lies inferiorly and laterally to the nerve, and then spirals around it from the lateral and superior sides.
Up to what level is the optic nerve covered by meninges?
Extensions of the dura, arachnoid, and pia mater cover the optic nerve along its entire length up to the sclera.
Where do the long ciliary nerves originate and what is their function?
They branch off from the nasociliary nerve (n. nasociliaris) and run in the adipose tissue above the optic nerve, providing sensory innervation to the eyeball.
Which muscles do the short ciliary nerves innervate?
They innervate m. ciliaris, m. sphincter pupillae, and m. dilatator pupillae, being responsible for adaptation and accommodation.
What else to study on this topic
- Topography of the lacrimal and supraorbital arteries in the orbital adipose tissue
- Formation of the sympathetic plexus around the ophthalmic artery
- Mechanism of accommodation during contraction of m. ciliaris
- Interaction of short and long ciliary nerves
- Anatomical features of the entry of ciliary arteries around the optic nerve
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