Lacrimal Glands

Lacrimal Gland

• Lobulated tubuloacinar gland
• Embryology: derived from surface ectoderm

• Situated within the zygomatic process of the frontal bone
• Possibly partially enclosed in periorbital connective tissue, but no true capsule

• 12 ducts secrete from orbital part into palpebral part then into superior fornix
• Ductules drain into the superotemporal fornix above the tarsus

• The ducts comprise secretory epithelial cells surrounded by myoepithelial cells

• Conical shaped columnar/cuboidal epithelial bilayer: with apices facing the central lumen

• Apical microvilli
• Basally located nuclei
• Rich in ER, Golgi, mitochondria
• Larger ducts have a double layer of lining cells
• Membrane bound secretory granules
• Histology is similar to salivary glands

• “Basal” tear film secretion is the result of light or temperature stimulation (plus proprioceptors in lids)

• Note: the lacrimal gland primarily performs reflex tear production

Arterial supply

• Lacrimal artery, branch of the ophthalmic (from internal carotid)
• Infraorbital artery, branch of maxillary (from external carotid)
• Ophthalmic vein drains
• Lymph drains to superficial parotid nodes

Nerve supply

• Higher control from reticular formation via descending autonomic pathways

• Secretomotor parasympathetic supply derives from superior salivatory nucleus (aka lacrimatory nucleus) of CNVII (facial nerve)

• Preganglionic fibres travel with nervus intermedius through middle ear
• Becomes the greater petrosal nerve
• Enters pterygopalatine fossa to synapse at pterygopalatine ganglion

• Postganglionic fibres hitch-hike with branches of maxillary nerve (zygomaticotemporal) and the lacrimal nerve (branch of ophthalmic).

• This innervation is responsible for reflex tearing

• Sensory innervation derives from trigeminal nerve: sensory ganglion, ophthalmic nerve and lacrimal branch

• Sympathetic innervation derives from T1 level sympathetic chain and superior cervical ganglion. These affect tear production by altering blood flow to the gland

• Post-ganglionic fibres from superior cervical ganglion travel in internal carotid plexus

• Join deep petrosal nerve

• Joins the vidian nerve and meets the pterygopalatine ganglion (but does not synapse here)

• Branches of the maxillary nerve become the zygomatic and zygomaticotemporal nerves and finally the lacrimal nerve

• Note: sympathetic and parasympathetic neurones both pass through the pterygopalatine ganglion

Drainage

• Punctum lacrimale sits upon the papillae lacrimalis, in line with tarsal glands
• The upper punctum sits medial to the lower punctum

• Lower canaliculus is slightly longer (10mm compared to 8mm)
• Both have approximately equal diameter (0.5mm)
• Canaliculi are lined by stratified squamous epithelium

• Common canaliculus enters nasolacrimal sac at 2.5mm from its apex (which histologically is a diverticulum of the sac called the sinus of Maier)

• Valve of Rosenmuller: where the superior and inferior canaliculi join to form the common canaliculus

• Medial palpebral ligament lies anteriorly

• Nasolacrimal sac is 12mm long
• Double layer of columnar epithelium
• Lies within lacrimal fossa: formed by lacrimal bone and frontal process of maxilla

• Enclosed in periorbita (fascia) but anterior to the orbital septum despite lying within the orbit

• Below the medial canthal tendon the sac is not enclosed in fascia and so is weaker
• Not covered in orbital fat
• Venous plexus lies between fascia and sac itself

• Nasolacrimal duct is continuous with sac
• Membranous structure
• 18mm long
• Thicker wall than the sac

• Travels within osseous nasolacrimal canal formed by a groove in the maxillary bone and laterally, by the lacrimal bone above and inferior nasal concha below

• Contains a venous plexus along two-thirds of its length
• Enters inferior meatus of nasal cavity
• Plica lacrimalis guards the opening (aka the valve of Hasner) into the inferior meatus

• Accessory lacrimal glands (in conjunctiva) are histologically identical to the lacrimal gland and produce identical secretions

Lacrimal caruncle

• Has colourless hair
• Contains accessory lacrimal glands
• Supplied by the infratrochlear nerve (branch of the nasociliary)
• Supplied by the superior medial palpebral artery: highly vascular
• Drains to the submandibular nodes