Lacrimal GlandEdit
The lacrimal gland is a paired exocrine gland of the orbit that produces the aqueous (watery) component of the tear film and contributes to the protection and lubrication of the ocular surface. Working in concert with the tear drainage system, blinking, and related ocular structures, it helps maintain a stable ocular surface environment essential for vision. As a core element of the lacrimal apparatus, the gland’s secretions are spread across the ocular surface and refreshed continually to support clear vision and immune defense on the surface of the eye.
Anatomy
Location and gross anatomy
The lacrimal gland sits in the superotemporal part of the orbit, within the lacrimal fossa of the frontal bone, above the lateral aspect of the eye. It is classically described as consisting of two lobes: an orbital lobe and a smaller palpebral lobe, which are connected by a slender bridge of tissue. The gland is surrounded by connective tissue and sits adjacent to the lacrimal gland ducts that deliver the aqueous secretion into the conjunctival sac. For context, the gland forms part of the broader Lacrimal apparatus alongside the tear drainage pathway.
Microanatomy
The secretory units of the lacrimal gland are serous acini composed of cells that produce the watery component of tears. Myoepithelial cells assist in expelling secretion into a ductal network, which ultimately channels fluid toward the conjunctival surface. The gland's architecture supports both basal tear production and reflex secretion in response to irritation or stimulation.
Innervation and vascular supply
Parasympathetic innervation of the lacrimal gland is primarily responsible for vigorous watery secretion and originates with the facial nerve. The signal travels via the greater petrosal nerve to the nerve of the pterygoid canal and the pterygopalatine ganglion, then reaches the gland through a relay with the zygomatic and lacrimal nerves. Sympathetic input, arising from the internal carotid plexus, modulates secretion and vascular tone but plays a comparatively smaller role in driving tear volume. The main arterial supply comes from the lacrimal artery, a branch of the ophthalmic artery, with venous drainage via the superior ophthalmic vein. Lymphatic drainage from the lacrimal gland generally communicates with regional nodes, including preauricular (parotid) nodes and deeper cervical nodes.
Relationship to surrounding structures
As part of the orbit, the lacrimal gland sits in proximity to the extraocular muscles, the lacrimal ducts, and the conjunctival fornices. Its position relative to the globe and eyelids makes it a central contributor to the tear film that covers the anterior surface of the eye.
Physiology and secretory function
Tear composition and the aqueous layer
Tears are a multi-layer fluid whose aqueous component serves to lubricate the ocular surface, provide nutrients to the epithelium, and host antimicrobial factors. The lacrimal gland supplies most of the aqueous fluid, rich in electrolytes, enzymes, and immune mediators that help defend against pathogens.
Secretory regulation
Autonomic control coordinates basal tear production and reflex tearing in response to environmental stimuli or ocular surface irritation. Parasympathetic input markedly increases watery secretion, while sympathetic activity modifies protein content and rate of secretion. The resulting tear film is a dynamic, three-layer system: a superficial lipid layer, a middle aqueous layer from the lacrimal gland and goblet cells, and a mucin layer that helps the film spread uniformly over the ocular surface.
Immune and antimicrobial components
Tears from the lacrimal gland contain antimicrobial proteins such as lysozyme, lactoferrin, and secretory immunoglobulin A (IgA), which contribute to defense against microbial invasion and help preserve corneal integrity.
Development and evolution
The lacrimal gland develops from surface ectoderm during fetal life, with differentiation and growth continuing through early adulthood. Its development and integration with the eyelids, conjunctiva, and nasolacrimal drainage system reflect the co-evolution of tear production and drainage mechanisms as a coordinated system for ocular protection and comfort.
Clinical significance
Dacryoadenitis and lacrimal gland masses
Inflammation of the lacrimal gland, termed dacryoadenitis, can be acute or chronic. Acute cases are often infectious (viral or bacterial) but may be inflammatory, autoimmune, or drug-induced. Chronic dacryoadenitis can reflect autoimmune diseases or chronic infections. Benign and malignant tumors can arise in the lacrimal gland, with pleomorphic adenoma being a common benign neoplasm and adenoid cystic carcinoma among malignant possibilities. Imaging and, when indicated, histopathology guide diagnosis and treatment planning.
Dry eye, lacrimal gland function, and autoimmune disease
Dysfunction or destruction of lacrimal gland tissue can contribute to dry eye syndromes, particularly in autoimmune conditions such as Sjögren's syndrome. In Sjögren's, immune-mediated infiltration reduces secretory capacity, diminishing the aqueous component of the tear film and destabilizing the ocular surface. Management involves addressing both local ocular surface disease and systemic autoimmune activity.
Tear drainage and epiphora
Obstruction or impairment of the nasolacrimal drainage system can lead to epiphora (excess tearing) and recurrent infections. Conditions such as nasolacrimal duct obstruction disrupt tear outflow, while functional tear drainage abnormalities may arise from neural or anatomic factors.
Diagnostics and imaging
Clinical assessment relies on history, examination of the orbit and lacrimal apparatus, and imaging when masses or drainage disorders are suspected. Imaging modalities include ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI) to characterize gland size, composition, and relationships to adjacent structures. Functional assessment of tear drainage can involve dacryoscintigraphy, which uses radiotracers to evaluate tear outflow through the lacrimal drainage system.