lacrimal gland

The lacrimal organs are part of the accessory apparatus of the eye, protecting the eyes from external influences and preventing the conjunctiva and cornea from drying out. The lacrimal organs produce and drain lacrimal fluid into the nasal cavity; they consist of the lacrimal gland, additional small lacrimal glands and lacrimal ducts. The lacrimal fluid produced by the lacrimal glands is of great importance for the normal function of the eye, as it moisturizes the cornea and conjunctiva. The ideal smoothness and transparency of the cornea, the correct refraction of light rays at its anterior surface are due, along with other factors, to the presence of a thin layer of lacrimal fluid covering the anterior surface of the cornea. Lacrimal fluid also helps cleanse the conjunctival cavity of microorganisms and foreign bodies, prevents the surface from drying out, and provides it with nutrition.

The orbital part of the lacrimal gland is laid down in the embryo at the age of 8 weeks. By the time of birth, lacrimal fluid is almost not secreted, since the lacrimal gland is not yet sufficiently developed. In 90% of children, active lacrimation begins only by the 2nd month of life. The lacrimal drainage apparatus is formed from the 6th week of embryonic life. An epithelial strand is immersed in the connective tissue from the orbital angle of the nasolacrimal groove, which gradually detaches itself from the initial epithelial covering of the face. By the 10th week, this strand reaches the epithelium of the lower nasal passage and by the 11th week turns into an epithelial-lined canal, which initially ends blindly and after 5 months opens into the nasal cavity. About 35% of children are born with the outlet of the nasolacrimal inflow closed by a membrane. If this membrane does not dissolve in the first weeks of a child's life, dacryocystitis of newborns may develop, requiring manipulation to create patency of tears through the canal into the nose.

The lacrimal gland consists of 2 parts: the upper, or orbital, part and the lower, or palpebral part. They are separated by a wide tendon of the muscle that raises the upper eyelid. The orbital part of the lacrimal gland is located in the fossa of the lacrimal gland of the frontal bone on the lateral-superior wall of the orbit. Its sagittal size is 10-12 mm, the frontal size is 20-25 mm, and the thickness is 5 mm. Normally, the orbital part of the gland is inaccessible to external examination. It has 3-5 excretory ducts passing between the lobes of the palpebral part, opening in the upper fornix of the conjunctiva laterally at a distance of 4-5 mm from the upper edge of the tarsal plate of the upper cartilage of the eyelid. The palpebral part of the lacrimal gland is significantly smaller than the orbital part and is located below it under the upper fornix of the conjunctiva on the temporal side. The size of the eyelid part is 9-11 x 7-8 mm, thickness - 1-2 mm. A number of excretory canals of this part of the lacrimal gland flow into the excretory canals of the orbital part, and 3-9 canals open independently. Multiple excretory canals of the lacrimal gland create a kind of "shower", from the openings of which tears enter the conjunctival cavity.

The lacrimal gland belongs to the complex tubular serous glands; its structure is similar to the parotid gland. The excretory ducts of larger caliber are lined with a two-layer columnar epithelium, and those of smaller caliber are lined with a single-layer cuboidal epithelium. In addition to the main lacrimal gland, there are small accessory tubular lacrimal glands: in the fornix of the conjunctiva - the conjunctival glands of Krause and at the upper edge of the cartilage of the eyelids, in the orbital part of the conjunctiva - Waldeyer's glands. In the upper fornix of the conjunctiva there are 8-30 accessory glands, in the lower - 2-4. The lacrimal gland is held in place by its own ligaments attached to the periosteum of the upper wall of the orbit. The gland is also strengthened by Lockwood's ligament, which suspends the eyeball, and the muscle that raises the upper eyelid. The lacrimal gland is supplied with blood from the lacrimal artery, a branch of the ophthalmic artery. Blood flows out through the lacrimal vein. The lacrimal gland is innervated by branches of the first and second branches of the trigeminal nerve, branches of the facial nerve and sympathetic fibers from the superior cervical ganglion. The main role in regulating the secretion of the lacrimal gland belongs to the parasympathetic fibers that are part of the facial nerve. The center of reflex lacrimation is located in the medulla oblongata. In addition, there are a number of other vegetative centers, the irritation of which increases lacrimation.

The lacrimal drainage system begins with the lacrimal stream. This is a capillary fissure between the posterior edge of the lower eyelid and the eyeball. The tears flow down the stream to the lacrimal lake, located at the medial node of the palpebral fissure. At the bottom of the lacrimal lake there is a small elevation - the lacrimal caruncle. The lower and upper lacrimal puncta are immersed in the lacrimal lake. They are located on the tops of the lacrimal papillae and normally have a diameter of 0.25 mm. The lower and upper lacrimal canaliculi originate from the puncta, which first go up and down for 1.5 mm, and then, bending at a right angle, go to the nose and flow into the lacrimal sac, more often (up to 65%) through a common mouth. At the place where they flow into the sac, a sinus is formed from above - the sinus of Mayer; there are folds of the mucous membrane: below - the Huschke valve, above - the Rosenmüller valve. The length of the lacrimal canals is 6-10 mm, lumen is 0.6 mm.

The lacrimal sac is located behind the internal ligament of the eyelids in the lacrimal fossa formed by the frontal process of the maxilla and the lacrimal bone. Surrounded by loose tissue and a fascial sheath, the sac rises 1/3 above the internal ligament of the eyelids with its vault, and below it passes into the nasolacrimal duct. The length of the lacrimal sac is 10-12 mm, the width is 2-3 mm. The walls of the sac consist of elastic and muscle fibers of the eyelid part of the orbicularis oculi - Horner's muscle - intertwined with them, the contraction of which facilitates the suction of tears.

The nasolacrimal duct, the upper part of which is enclosed in the bony nasolacrimal canal, passes in the lateral wall of the nose. The mucous membrane of the lacrimal sac and nasolacrimal duct is delicate, has the character of adenoid tissue, lined with cylindrical, in places ciliated epithelium. In the lower parts of the nasolacrimal duct, the mucous membrane is surrounded by a dense venous network of the cavernous tissue type. The nasolacrimal duct is longer than the bony nasolacrimal canal. At the exit into the nose there is a fold of the mucous membrane - the lacrimal valve of Gasner. The nasolacrimal duct opens under the anterior end of the inferior turbinate at a distance of 30-35 mm from the entrance to the nasal cavity in the form of a wide or scallop-like opening. Sometimes the nasolacrimal duct passes in the form of a narrow canal in the mucous membrane of the nose and opens to the side of the opening of the bony nasolacrimal canal. The last two variants of the nasolacrimal duct structure can cause rhinogenic disorders of lacrimation. The length of the nasolacrimal duct is from 10 to 24 mm, the width is 3-4 mm.

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Lacrimal apparatus of the eye

The lacrimal apparatus (apparatus lacrimalis) includes the lacrimal gland with its excretory canals opening into the conjunctival sac, and the lacrimal drainage ducts. The lacrimal gland (glandula lacrimalis) is a complex alveolar-tubular gland of lobular structure, located in the pit of the same name in the lateral angle, in the upper wall of the orbit. The tendon of the muscle that raises the upper eyelid divides the gland into a larger upper orbital part (pars orbitalis) and a smaller lower eyelid part (pars palpebralis), located near the upper fornix of the conjunctiva.

Under the fornix of the conjunctiva, small accessory lacrimal glands (glandulae lacrimales accessoriae) are sometimes found. Up to 15 excretory canals (ductuli excretorii) of the lacrimal gland open into the conjunctival sac in the lateral part of the superior fornix of the conjunctiva. The tears (lacrimal fluid) coming out of the canals wash the anterior part of the eyeball. Then the lacrimal fluid flows through the capillary slit near the edges of the eyelids along the lacrimal stream (rivus lacrimals) into the area of the medial angle of the eye, into the lacrimal lake. This is where the short (about 1 cm) and narrow (0.5 mm) curved upper and lower lacrimal canaliculi (canaliculi lacrimales) originate. These canaliculi open into the lacrimal sac separately or connected to each other. The lacrimal sac (saccus lacrimalis) lies in the fossa of the same name in the lower medial angle of the orbit. At the bottom it passes into a fairly wide (up to 4 mm) nasolacrimal duct (ductus nasolacrimalis), ending in the nasal cavity, in the anterior part of the inferior nasal passage. The lacrimal part of the orbicularis oculi muscle is fused with the anterior wall of the lacrimal sac, which, when contracted, expands the lacrimal sac, which facilitates the absorption of lacrimal fluid into it through the lacrimal canals.