Ophthalmic nerve (CN V1)
The ophthalmic nerve (first division of fifth cranial nerve, ophthalmic division of trigeminal nerve, first division of trigeminal nerve, CN V1, latin: nervus ophthalmicus) is the first branch of the trigeminal nerve. The ophthalmic nerve is a sensory nerve mostly carrying general somatic afferent fibers that transmit sensory information to the CNS from structures of the eyeball, the skin of the upper face and anterior scalp, the lining of the upper part of the nasal cavity and air cells, and the meninges of the anterior cranial fossa. Some of ophthalmic nerve branches also convey parasympathetic fibers.
The ophthalmic nerve arising from the trigeminal ganglion in the middle cranial fossa passes forwards along the lateral dural wall of the cavernous sinus below the trochlear nerve (CN IV). Before entering the sinus the ophthalmic nerve gives off a tentorial branch to innervate the dura mater. The ophthalmic nerve reaches the orbit passing through the superior orbital fissure. Just before it reaches the fissure the nerve gives off three major branches:
- frontal nerve,
- lacrimal nerve,
- nasociliary nerve.
The frontal nerve is a sensory nerve arising from the ophthalmic nerve (CN V1). The frontal nerve runs by the roof of the orbit and while in orbit divides into two nerves - the supratrochlear and supraorbital nerve, which arise on the face and together innervate the skin of the forehead.
The supratrochlear nerve is a branch of the frontal nerve (coming from the ophthalmic nerve) that provides the conjunctiva of the upper eyelid and the skin covering the upper eyelid, and areas of the forehead with sensory innervation.
The supratrochlear nerve runs medially above trochlea for the tendon of superior oblique muscle. It gives a descending branch to the infratrochlear nerve and ascends on to the forehead through the frontal foramen or notch.
The areas innervated by the supratrochlear nerve in the face are: the conjunctiva and skin covering the upper eyelid and forehead.
The supraorbital nerve is the largest of the two terminal branches of the frontal nerve that innervates the mucosa of the frontal sinus, the conjunctiva and skin of the upper eyelid, and the skin of the forehead and the scalp.
The supraorbital nerve arises in the orbit from the frontal nerve, which is a branch of the ophthalmic nerve (CN V1), and continues forward along the levator palpebrae superioris muscle and leaves the orbit through the supra-orbital notch or foramen. After appearing in the tissue of the forehead the supraorbital nerve ascends and ends in two branches, the medial and the lateral branch of the supraorbital nerve, which innervate the scalp, as well as supplying small branches to pericranium.
The lateral branch is one of the two terminal branches of the supraorbital nerve. First situated beneath the frontalis muscle the lateral branch of the supraorbital nerve perforates the galea aponeurotica to innervate the skin of the forehead and scalp.
The medial branch is one of the two terminal branches of the supraorbital nerve. First situated beneath the frontalis muscle the medial branch of the supraorbital nerve perforates the frontalis muscle to innervate the skin of the forehead and scalp.
To sum up, the structures innervated by the supraorbital nerve are: the mucous membrane lining the frontal sinus, the conjunctiva and skin covering the upper eyelid, and the skin over the forehead and extending nearly up to the middle of the scalp.
The lacrimal nerve is a branch of the ophthalmic nerve (CN V1) that enters the orbit through the superior orbital fissure and provides sensory innervation for the lacrimal gland, the conjunctiva and skin covering the lateral part of the upper eyelid.
The lacrimal nerve enters the orbit through the superior orbital fissure, outside the common tendinous ring and lateral to the frontal and trochlear nerves. The lacrimal nerve goes forward along the lateral wall of the orbit and passes through the lacrimal gland and orbital septum. The nerve has a communicating branch with the zygomatic nerve.
The communicating branch with zygomatic nerve refers to the anastomosis which serves as the link between the zygomaticotemporal branch of the zygomatic nerve (from maxillary nerve, CN V2) and the lacrimal nerve (from ophthalmic nerve, CN V1). This communicating branch carries some of the postganglionic parasympathetic fibers from the pterygopalatine ganglion to the lacrimal gland inhibiting its glandular secretion.
The nasociliary nerve is a branch of the ophthalmic nerve (CN V1) that enters the orbit through superior orbital fissure. The main areas supplied by this sensory nerve and its branches are the mucosa of the nasal cavity, skin of the nasal root, as well as the skin and conjunctiva of the medial corner of the eye.
The nasociliary nerve enters the orbit through the common tendinous ring, lying between the two divisions of the oculomotor nerve (CN III), crosses the optic nerve (CN II) and the ophthalmic artery, and runs obliquely below the superior rectus and superior oblique muscles. Then the nasociliary nerve travels along the medial orbital wall and terminates as the infratrochlear nerve. On its way the nasociliary nerve gives off several branches:
- posterior ethmoidal nerve;
- anterior ethmoidal nerve;
- long ciliary nerves;
- sensory root of ciliary ganglion.
The posterior ethmoidal nerve is a branch of the nasociliary nerve, which leaves the orbit via the posterior ethmoidal foramen and supplies the mucous of the ethmoidal and sphenoidal sinuses, and the nasal cavity with sensory fibers.
The anterior ethmoidal nerve is a branch of the nasociliar nerve leaving the orbit through the anterior ethmoidal foramen, entering the anterior ethmoidal sinuses. The anterior ethmoidal nerve has a role in regulating mucous levels of the nasal cavity and provides sensory innervation to some of the skin of the nose.
The anterior ethmoidal nerve passes through the anterior ethmoidal foramen and canal, entering the anterior ethmoidal sinuses, giving off branches to supply the anterior and medial ethmoidal sinuses. The ethmoidal nerve then enters the cranial cavity, specifically, the anterior cranial fossa, where it gives a meningeal branch to innervate the dura in this area. The anterior ethmoidal nerve runs forwards in a groove on the upper surface of the cribriform plate beneath the dura mater, and descends through a slit lateral to the crista galli into the nasal cavity, where it occupies a groove on the internal surface of the nasal bone and gives off the internal nasal branches. The terminal branch called the external nasal branch of the anterior ethmoidal nerve penetrates the nasal bone and appears on the face, innervating skin in the areas of the nasal dorsum and the apex of the nose.
Two or three long ciliary nerves branch from the nasociliary nerve as it crosses the optic nerve. They accompany the short ciliary nerves, pierce the sclera near the attachment of the optic nerve (CN II), and run forwards between the sclera and choroid. The long ciliary nerves carry sensory fibers which innervate the ciliary body, iris and cornea, as well as contain postganglionic sympathetic fibers, arising from neurons in the superior cervical ganglion, for the dilatator pupillae.
The sensory root of the ciliary ganglion refers to sensory nerve fibers originating in the structures of the eyeball, such as the cornea, the iris, and the ciliary body, which are carried by a communicating branch to the ciliary ganglion of the nasociliary nerve. The fibers of the sensory root of the ciliary ganglion pass through the ciliary ganglion without forming synapses.