Ophthalmic branch of the trigeminal nerve
The trigeminal nerve can be daunting when it comes to studying its anatomy. It has many functions, and even though it possesses only three major branches, each one of them is highly important and anatomically complex.
The ophthalmic nerve is one of the branches of the trigeminal nerve, otherwise known as the fifth cranial nerve (CN V). Supplying sensory innervation to certain parts of the eye, the lacrimal gland, some paranasal sinuses, meningeal layers, and the scalp this nerve allows you to blink quickly when dust gets in the eye, for example.
In this article, the ophthalmic nerve, as the branch of the trigeminal nerve, is going to be fully explained from the aspect of general anatomy, function, and clinical importance.
|Course||Trigeminal ganglion -> cavernous sinus -> superior orbital fissure -> lacrimal, frontal, nasociliary nerves (terminal branches) -> respective anatomical structures|
|Branches||Recurrent tentorial, lacrimal (communicating branch with zygomatic nerve), frontal (supraorbital and supratrochlear nerves), nasociliary nerves (communicating branch with the ciliary ganglion, ciliary nerves, posterior ethmoid nerves)|
|Innervation||Eyes, conjunctiva, lacrimal gland, nasal cavity, frontal sinus, ethmoidal cells, falx cerebri, dura mater of anterior cranial fossa, superior parts of tentorium cerebelli, upper eyelid, dorsum of nose, anterior part of the scalp|
The trigeminal nerve (cranial nerve V) is a mixed nerve, meaning that it is made of both fiber types: descending motor (efferent) fibers and afferent neural fibers that belong to the general somatic afferent system. The trigeminal nerve leaves the pons via two roots:
- Large sensory root
- Smaller motor root
These roots continue coursing forward out of the posterior cranial fossa. The fibers enter the middle cranial fossa by passing over the medial tip of the petrous part of the temporal bone. In the depression on the anterior surface of the petrous part of the temporal bone, the trigeminal ganglion can be found. For this reason, this depression is called the trigeminal depression, and the ganglion itself is wrapped within the dura mater in a cave-like appearance; it is called the trigeminal cave. This ganglion is the expansion of the sensory root and it contains the bodies of the sensory neurons whose fibers contribute to the making of the trigeminal nerve. Functionally, this ganglion is comparable to a spinal ganglion.
From the anterior edge of the trigeminal ganglion arise three branches of the trigeminal nerve in the following descending (superior to inferior) order:
The ophthalmic nerve is the most superior branch of the trigeminal ganglion, and it is exclusively sensory. It provides sensory information to the following structures:
- The eyes
- Conjunctiva and orbital contents including the lacrimal gland
- Nasal cavity, frontal sinus, ethmoidal cells
- Falx cerebri
- Dura mater of the anterior cranial fossa
- Superior parts of the tentorium cerebelli
- Upper eyelid
- Dorsum of the nose
- Anterior part of the scalp
During its pathway, this nerve also receives sympathetic fibers that project to the autonomous ciliary ganglion. Some authors describe this ganglion as belonging to the oculomotor nerve.
Course and relations
The ophthalmic nerve arises from the anterior edge of the trigeminal ganglion and then extends forward through the lateral wall of the dura mater of the cavernous sinus. Superior to the ophthalmic nerve is the trochlear nerve, whereas inferolateral to it is the maxillary nerve. Medial to all of these three nerves is located the internal carotid artery that goes through the cavernous sinus.
After leaving the cavernous sinus, the ophthalmic nerve goes through the superior orbital fissure, where it is usually already divided into its three terminal branches:
- Lacrimal nerve
- Frontal nerve
- Nasociliary nerve
Along its pathway, the ophthalmic nerve extends to a number of lateral branches. The most important of them is the recurrent tentorial nerve that courses backward and innervates the tentorium cerebelli. Besides this branch, most of the significance is given to the terminal branches of the ophthalmic nerve.
This is the most lateral and thinnest branch of the ophthalmic nerve. It extends forward and laterally, across the roof of the orbit and travels towards the lacrimal gland that is located in the upper lateral angle of the orbit. Before it reaches the gland, the lacrimal nerve extends to several branches. These branches either terminate in the lacrimal gland, or they pass through the gland and end in the upper eyelid.
Just behind the lacrimal gland, the lacrimal nerve extends a communicant branch for the zygomatic nerve. Through this anastomosis, the parasympathetic fibers from the pterygopalatine ganglion reach the lacrimal gland. These fibers originate from the petrosal nerve of the facial nerve.
This is the middle and thickest branch of the ophthalmic nerve. It courses forwards, directly beneath the roof of the orbit and superiorly to the superior palpebral levator muscle. Inside the orbit, the nerve extends to both of its terminal branches:
- The supraorbital nerve is the lateral branch of the frontal nerve. It reaches the forehead by passing through the supraorbital notch. At this level, the nerve gives off several palpebral filaments that supply the conjuctiva and the skin of the upper eyelid. It then courses superiorly over the forehead along with the supraorbital artery. Deep to the frontal belly of occipitofrontalis muscle, the supraorbital nerve splits into two of its own terminal branches; lateral branch and medial branch. The medial branch penetrates the occipitofrontalis muscle, while the lateral passes through the epicranial aponeurosis. In this way, the branches reach the skin of the lower forehead which they provide with sensory innervation.
- The supratrochlear nerve is placed medial to the supraorbital nerve. It courses medially and forward, traveling to the superior medial angle of the orbit. It extends to the superior and inferior branches that innervate the skin of the dorsum of the nose and adjacent skin of the upper eyelid.
This nerve is the medial terminal branch of the ophthalmic nerve. It courses forward and medially, and by crossing over the superior side of the optic nerve it reaches the anterior ethmoid foramen, where it divides to its own two terminal branches. Along its way, the nasociliary nerve extends to the lateral branches in the following order going from proximal to distal to the root:
- Communicant branch for the ciliary ganglion that extends forward and laterally, and enters the ciliary ganglion.
- Long and short ciliary nerves that penetrate the posterior part of the sclera medially to the optic nerve. In this way, these nerves enter the eyeball and innervate the sclera and the choroidea.
- Posterior ethmoid nerve that extends medially through the posterior ethmoid foramen and enters the anterior cranial fossa. As it passes through one of the foramina of the lamina cribrosa, it descends to the roof of the nasal cavity where it innervates the mucosa of the ethmoid cells and sphenoid sinus.
In the area of the anterior ethmoid foramen, the nasociliary nerve extends to its two terminal branches:
- The anterior ethmoid nerve passes through the anterior ethmoid foramen where it reaches the anterior cranial fossa. Soon after that, the nerve goes through one of the foramina of the lamina cribrosa, through which it reaches the anterior part of the roof of the nasal cavity, where it innervates the mucosa of that part.
- The infratrochlear nerve which extends forward and inferiorly to the trochlea travels towards the superior medial angle of the orbit, where it sends its terminal branches for the innervation of the skin of the medial portion of the upper eyelid and the conjunctiva. Branches of this nerve enable the so-called conjunctival reflex.
This ganglion belongs to the autonomic nervous system and is functionally added to the ophthalmic nerve. It is placed in the orbit, on the lateral side of the optic nerve. Like any other autonomic ganglion, the ciliary ganglion has preganglionic and postganglionic fibers. Preganglionic fibers are sensory, sympathetic and parasympathetic. These are:
- Communicant branches to the ciliary ganglion that extend from the nasociliary nerve and carry the sensory and sympathetic fibers to this ganglion. Sensory fibers originate from the sensory root of the trigeminal nerve, whereas the sympathetic fibers originate from the sympathetic internal carotid plexus and its anastomosis with the ophthalmic nerve.
- Oculomotor root provides the parasympathetic fibers from the oculomotor nerve and those fibers synapse with the cells of the ganglion.
Postganglionic fibers are the short ciliary nerves that extend forward while grouped around the optic nerve. They penetrate the posterior part of the sclera and enter the eyeball to which they bring the sensory and the autonomic neuronal fibers. Parasympathetic fibers innervate the ciliary muscle and the pupil sphincter muscle, whereas the sympathetic fibers innervate the pupil dilator muscle. Both dilatation and constriction of the pupil are the mechanisms that take part in the eye accommodation. Also, this specific innervation is the reason why pupils dilate during stress (domination of the sympathetic nervous system), and narrow when relaxed (domination of the parasympathetic nervous system).
Damages to the ophthalmic nerve can cause symptoms related to sensory dysfunctions. Infections of the trigeminal ganglion by the herpes zoster virus (shingles) will cause very painful sensations among all of the areas that are sensory innervated by the trigeminal nerve, but will mostly affect the areas innervated by the ophthalmic nerve. The infection may eventually result in the complete loss of the sensation within the affected parts.
A procedure called supraorbital nerve block is often used to achieve the local anesthesia of the face. As the name says for itself, the target structure is the supraorbital nerve, a branch of the frontal nerve, which again, is a terminal branch of the ophthalmic nerve. It is a convenient way of preventing the tissue distortion and the uncomfortable sensations for the patient while performing various surgical procedures in the region of the forehead that is innervated by this nerve.
Dysfunctions of the ophthalmic nerve can be joined to the dysfunctions of the facial nerve within the condition called Bell’s palsy. This condition mostly affects the structures innervated by the facial nerve and sometimes includes branches of the trigeminal nerve where sensory disorders of all the structures innervated by this nerve can manifest. This condition is usually caused by the inflammation of the nerve that is in most cases caused by neurotropic viruses, such as herpes simplex virus type-1, HIV, and herpes zoster.
The ophthalmic nerve is a part of the corneal reflex, and together with the maxillary nerve, the palpebral reflex. In normal situations, the stimulation of the cornea or a sudden object close to the eyes will cause automatic closing of the eyelids as a form of a protective reflex. When the ophthalmic nerve is damaged, there is a lack of these reflexes.
We can conclude that the ophthalmic nerve is of great importance when it comes to the basic neurology evaluation of a patient. Being familiar with the fields of its innervations is crucial since it provides strong foundations of knowledge for today's students and tomorrow's future doctors.