Thus, the nasociliary nerve is formed by the joining of the infratrochlear nerve, the anterior and posterior ethmoid nerves, the long ciliary nerves, and the sensory root of the ciliary ganglion (see Figure 12-1). The nasociliary nerve exits the orbit by passing through the oculomotor foramen within the common tendinous ring and the superior orbital fissure into the cranial cavity.

Clinical Comment: Herpes Zoster

HERPES ZOSTER  is an acute CNS infection caused by the varicella-zoster virus. Signs and symptoms include pain and rash in the distribution area supplied by the affected sensory nerves.9 It is believed that the virus lies dormant in a sensory ganglion and, on becoming ­activated, migrates down the sensory pathway to the skin.10 An eruption

of herpes zoster is more common in elderly persons but may occur at any age and may be related to a delayed ­hypersensitivity reaction.11 Approximately 10% of all cases affect the ophthalmic division of the trigeminal nerve.12 Involvement of the tip of the nose often indicates that

the eye will also be involved, reflecting the distribution of the nasociliary branches. This association of ocular

involvement with zoster affecting the tip of the nose is the Hutchinson sign.13

Frontal Nerve

Sensory fibers from the skin and muscles of the forehead and upper eyelid come together and form the supratrochlear nerve. This nerve enters the orbit by piercing the superior medial corner of the orbital septum (Figure 12-4).

Sensory fibers from the skin and muscles of the forehead and upper eyelid form a second nerve, the supraorbital nerve, lateral to the supratrochlear nerve. The supraorbital nerve enters the orbit as one or two branches: one branch enters through the supraorbital notch, accompanying the supraorbital artery. The supraorbital nerve joins the supratrochlear nerve midway in the orbit and forms the frontal nerve (see Figure 12-1). The frontal nerve courses back through the orbit between the levator muscle and the periorbita, exiting the orbit through the superior orbital fissure above the common tendinous ring.

Lacrimal Nerve

Sensory fibers from the lateral aspect of the upper eyelid and temple area come together and enter the lacrimal gland; they join the sensory fibers that serve the gland itself to form the lacrimal nerve. The lacrimal nerve leaves the gland and runs posteriorly

Supraorbital

nerve

Supratrochlear Lacrimal nerve

nerve

Infratrochlear nerve

Zygomatico-

facial nerve

Infraorbital nerve

FIGURE 12-4

Sensory innervation to upper and lower eyelids.

along the upper border of the lateral rectus muscle (see Figure 12-1). It receives a branch from the zygomatic nerve containing the autonomic innervation of the lacrimal gland. The lacrimal nerve exits the orbit through the superior orbital fissure above the muscle cone.

Ophthalmic Nerve Formation

After exiting the orbit, the nasociliary nerve, the lacrimal nerve, and the frontal nerve join and form the ophthalmic division of the trigeminal nerve (see Figure­ 12-1). The ophthalmic nerve then enters the lateral wall of the cavernous sinus, coursing between the two dural layers.14 While in the wall of the sinus the nerve receives sensory fibers from the oculomotor, trochlear, and abducens nerves. Some of these fibers probably carry proprioceptive information from the extraocular muscles.15

Maxillary Division of Trigeminal Nerve

Infraorbital Nerve

The infraorbital nerve, formed by sensory fibers from the cheek, upper lip, and lower eyelid, enters the maxillary bone through the infraorbital foramen (Figure 12-5). It runs posteriorly through the infraorbital canal and groove; while it is in the maxillary bone, branches join from the upper teeth and maxillary sinus. As the nerve leaves the infraorbital groove it exits the orbit through the inferior orbital fissure and joins other fibers in forming the maxillary nerve.