The main lacrimal gland is located in a shallow depression within the orbital part of the frontal bone. The gland is separated from the orbit by fibroadipose tissue and is divided into 2 parts, orbital and palpebral lobes, by the lateral horn of the levator aponeurosis (Fig 1-38). When the upper eyelid is everted, the smaller palpebral lobe can be seen in the superolateral conjunctival fornix. An isthmus of glandular tissue may exist between the palpebral lobe and the larger orbital lobe.
A variable number of thin-walled excretory ducts, blood vessels, lymphatics, and nerves pass from the orbital lobe into the palpebral lacrimal gland. The ducts continue downward, and about 12 of them empty into the conjunctival fornix approximately 5 mm above the superior margin of the upper tarsus.
Figure 1-38 The lacrimal secretory system. The conjunctival and tarsal mucin-secreting goblet cells (green) contribute to the mucoaqueous and glycocalyx components of the tear film. The accessory lacrimal exocrine glands of Krause and Wolfring are pres ent in the subconjunctival tissues (blue) and contribute to the aqueous component of the tear film. Oil-producing meibomian glands and palpebral glands of Zeis and Moll are shown in pink. The orbital lobe of the lacrimal gland (Lo) and the palpebral lobe of the lacrimal gland (Lp) are separated by the lateral horn of the levator aponeurosis (Ap). The tear ducts (arrow) from the orbital portion traverse the palpebral portion. The levator palpebrae superioris (LPS) muscle and the Whitnall ligament (Wh) are also shown.
(Modified with permission from Zide BM, Jelks GW. Surgical Anatomy of the Orbit. New York: Raven; 1985.)
The lacrimal glands are exocrine glands that produce a serous secretion. The body of each gland contains 2 cell types (Fig 1-39):
glandular epithelial cells, which line the lumen of the gland
myoepithelial cells, which surround the parenchyma and are covered by a basement membrane
Lacrimal secretions comprise the aqueous component of the tear film and include lysozymes, lactoferrin, and immunoglobulin A. The lacrimal gland undergoes structural and functional alterations with age, which may play a role in acquired dry eye.
The lacrimal artery, a branch of the ophthalmic artery, supplies the gland with blood. The lacrimal gland receives secretomotor cholinergic, vasoactive intestinal polypeptide (VIP)-ergic, and sympathetic nerve fibers in addition to sensory innervation via the lacrimal nerve (from CN V1). The gland’s extremely complex neuroanatomy governs both reflex and psychogenic stimulation (see BCSC Section 5, Neuro-Ophthalmology).
Figure 1-39 Lacrimal gland lobule. A, Low magnification of lacrimal gland lobule demonstrating its central duct (arrow).B, Histologic section of the lacrimal gland demonstrating acinar units (Ac) made up of a central lumen surrounded by glandular epithelial cells with secretory granules. Arrows indicate surrounding myoepithelial cells. The stroma contains blood vessels and numerous plasma (P) cells that produce immunoglobulin A. C, Schematic of the lacrimal lobule.
(Modified with permission from Forrester JV, Dick AD, McMenamin PG, Roberts F, Pearlman E. The Eye: Basic Sciences in Practice. 4th ed. Edinburgh: Elsevier; 2016:90.)
Rocha EM, Alves M, Rios JD, Dartt DA. The aging lacrimal gland: changes in structure and function. Ocul Surf. 2008;6(4):162–174.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.