Lacrimal Gland

Lobulated tubuloacinar gland
Embryology: derived from surface ectoderm

The gland is divided into a larger orbital (superior) lobe and smaller palpebral lobe separated by the aponeurosis of levator

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

The pre-aponeurotic fat does not extend to cover the gland (so important not to mistake gland for fat during blepharoplasty or other upper lid surgery).

12 ducts secrete from orbital part into palpebral part then into superior fornix

Ductules drain into the superotemporal fornix above the tarsus

The palpebral lobe contains secretory ducts for both portions. Therefore biopsy of the palpebral lobe is more likely to impair tear production

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

The canaliculi have 2mm vertical portion and 10mm horizontal portion with dilation at the junction (ampulla)

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

Orbicularis oculi lies posterior but its pretarsal fibres surround the canaliculi: pumping action compresses canaliculi and dilates sac causing tears to be sucked into sac

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

The angular vein crosses the sac anteriorly

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

The duct is the most common site for acquired obstruction of the lacrimal system

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

The valve of Hasner is the most common site for congenital obstruction

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