The lacrimal glands are serous type exocrine glands that secrete lacrimal fluid onto the surfaces of the conjunctiva and cornea of the eye. This fluid serves to clean, nourish, and lubricate the eye, and when produced in excess, forms tears.
In this article, we shall look at the anatomy of the lacrimal glands - their location, neurovascular supply, and clinical relevance.
The lacrimal gland is located anteriorly in the superolateral aspect of the orbit, within the lacrimal fossa – a depression in the orbital plate of the frontal bone.
Its anatomical relations include:
The lacrimal gland is approximately two centimeters long and can be divided into two main parts:
The lacrimal gland is a compound tubuloacinar gland, comprised of lobules which are formed by multiple acini. These acini contain serous cells and produce a watery serous secretion (lacrimal fluid). This fluid is secreted into excretory ducts, which empty into the superior conjunctival fornix. The fluid is then spread over the cornea by the process of blinking.
The lacrimal apparatus is the system responsible for the drainage of lacrimal fluid from the orbit. After secretion, lacrimal fluid circulates across the eye and accumulates in the lacrimal lake, located in the medial canthus of the eye. From here, it drains into the lacrimal sac via a series of canals.
The lacrimal sac is the dilated end of the nasolacrimal duct and is located in a groove formed by the lacrimal bone and frontal process of the maxilla. Lacrimal fluid drains down the nasolacrimal duct and empties into the inferior meatus of the nasal cavity.
The main arterial supply to the lacrimal gland is from the lacrimal artery, which is derived from the ophthalmic artery – a branch of the internal carotid. Venous drainage is via the superior ophthalmic vein, and ultimately empties into the cavernous sinus. Lymphatic drainage is to the superficial parotid lymph nodes, which empty into the superior deep cervical nodes.
The sensory innervation to the lacrimal gland is via the lacrimal nerve, which is a branch of the ophthalmic nerve, in turn derived from the trigeminal nerve. The lacrimal gland also receives autonomic nerve fibres, with the parasympathetic stimulating fluid secretion from the lacrimal gland and the sympathetic inhibiting it.
The parasympathetic preganglionic fibres are carried in the greater petrosal nerve (branch of the facial nerve) and then the nerve of pterygoid canal, before synapsing at the pterygopalatine ganglion. Postganglionic fibres travel with the maxillary nerve, and finally the zygomatic nerve. The sympathetic fibres originate from the superior cervical ganglion and are carried by the internal carotid plexus and deep petrosal nerve.
These join with the parasympathetic fibres in the nerve of pterygoid canal, and follow the same route to supply the gland.
Dacryoadenitis is the inflammation of the lacrimal glands. This could present acutely or chronically, with acute dacryoadenitis typically due to viral or bacterial infections such as mumps, Epstein-Barr virus, staphylococcus, and gonococcus; while chronic dacryoadenitis usually due to a non-infectious inflammatory condition such as sarcoidosis or thyroid eye disease associated with Grave’s disease.
Clinical features of dacryoadenitis include swelling, pain, and excess tear production.
The lacrimal glands are two small almond-shaped organs located near the temporal margin of the eye orbits. Anatomically, these glands have superior relations with the zygomatic process of the frontal bone, anterior relations with the orbital septum, posterior relations with orbital fat, and inferolateral relations with the lateral rectus muscle. The lacrimal glands measure an approximate 2 cm long and can be divided into two main parts. The larger part, the orbital portion, sits on the outer margin of the levator palpebrae superioris muscle. The other smaller part, the palpebral portion, is located along the inner surface of the eyelid. It is a compound tubuloacinar gland, comprised of lobules which are formed by multiple acini containing serous cells which produce a watery serous secretion, known as the lacrimal fluid.
The lacrimal fluid is secreted into excretory ducts which ultimately empty into the superior conjunctival fornix. During blinking, the fluid is spread over the cornea due to the lacrimal apparatus. This is the system responsible for the drainage of lacrimal fluid from the orbit. The lacrimal lake, which is located in the medial canthus of the eye, collects the fluid and then drains it into the lacrimal sac through a series of canals.
The lacrimal sac is the dilated end of the nasolacrimal duct and is located in a groove formed by the lacrimal bone and frontal process of the maxilla. The lacrimal fluid then drains down from the sac and empties into the inferior meatus of the nasal cavity. The main arterial supply to the lacrimal glands is from the lacrimal artery, which is a branch of the internal carotid artery. Venous drainage is via the superior ophthalmic vein, which empties into the cavernous sinus. Lymphatic drainage is to the superficial parotid lymph nodes, which empty into the superior deep cervical nodes.
The sensory nerves to the lacrimal glands are carried by the lacrimal nerve, which is a branch of the ophthalmic nerve itself a branch of the trigeminal nerve (CN V). The autonomous nerve fibres of the lacrimal glands are derived from both the parasympathetic and sympathetic nervous system. The preganglionic parasympathetic fibres are carried in the greater petrosal nerve, then the nerve of pterygoid canal, before synapsing at the pterygopalatine ganglion. Postganglionic fibres travel with the maxillary nerve, and then the zygomatic nerve. These fibres stimulate fluid secretion from the lacrimal glands. The sympathetic fibres originate from the superior cervical ganglion and are carried by the internal carotid plexus and deep petrosal nerve. These fibers then join with the parasympathetic fibres and follow the same route to supply the lacrimal glands, but instead they inhibit fluid secretion.
Dacryoadenitis refers to inflammation of the lacrimal glands. It can present acutely or chronically. Acute dacryoadenitis is usually due to a viral or bacterial infection, such as mumps, Epstein-Barr virus, staphylococcus and gonococcus, commonly causing swelling, pain and excess tear production. Chronic dacryoadenitis is generally caused by a non-infectious inflammatory condition such as sarcoidosis or thyroid eye disease associated with Grave's disease. Visual impairment is a common secondary symptom caused due to the swelling of the gland, which puts pressure on the eye. Treatment methods depend on the cause. If the cause is viral, then a simple rest and warm compresses would be helpful to reduce the swelling. In other cases, it is necessary to treat the underlying cause for effective results.
