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Anatomy of the Lacrimal System

Anatomy

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1. Lacrimal System

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Clinical Analogy - The Building’s Plumbing
  • Think of the lacrimal apparatus as a building’s plumbing system.
  • The lacrimal gland is the overhead water tank (secretory source).
  • The tear film is water flowing across the floor (ocular surface).
  • The puncta are the floor drains.
  • The canaliculi are the drainage pipes.
  • The lacrimal sac is the holding cistern.
  • The nasolacrimal duct (NLD) is the main sewer pipe that drains into the nasal cavity (inferior meatus).
  • Any blockage - from the drain inlets (punctal stenosis) to the main pipe (nasolacrimal duct [NLD] obstruction) - causes overflow (epiphora).
  • Surgeons bypass the obstruction by creating a new window from the cistern directly to the nose (dacryocystorhinostomy [DCR]).

2. Overview of the Lacrimal Apparatus

  • The lacrimal apparatus has two functionally distinct components:
  • (A) the secretory system responsible for tear production, and
  • (B) the excretory (drainage) system responsible for tear elimination.
  • Mastery of both is essential for managing epiphora, dry eye, dacryocystitis, and lacrimal surgery.

Secretory System

Main Lacrimal Gland

  • A lobulated tubulo-acinar exocrine gland with mixed serous and mucinous acini in the lacrimal fossa of the frontal bone (superolateral orbit).
  • The lateral horn of the levator aponeurosis divides it into two lobes:
  • Orbital lobe (Pars orbitalis): Larger (~20 × 12 mm); lies above the aponeurosis in the bony fossa.
  • Palpebral lobe (Pars palpebralis): Smaller; lies below the aponeurosis; directly visible on upper lid eversion at the lateral fornix.
  • Both lobes drain via approximately 8–12 excretory ductules, mainly arising from the orbital lobe and passing through the palpebral lobe, into the superior temporal conjunctival fornix (lateral one-third).
  • The two lobes are continuous around the lateral edge of the levator aponeurosis, and ducts from the orbital lobe pass through the palpebral lobe; therefore, surgical trauma to the palpebral lobe can disrupt drainage from the orbital lobe.
Exam pearl
  • Removal of the palpebral lobe alone can functionally ablate the entire main lacrimal gland's secretory output.

Neurovascular Anatomy of the Lacrimal Gland

ComponentDetail
ArteryLacrimal artery (ophthalmic artery branch, from internal carotid artery (ICA))
VeinDrains to ophthalmic vein → cavernous sinus
Sensory nerveLacrimal nerve (ophthalmic division (V1) of trigeminal)
Parasympathetic (secretomotor)• Superior salivatory nucleus (pons) • nervus intermedius • geniculate ganglion • greater petrosal nerve • nerve of the pterygoid canal (Vidian nerve) • pterygopalatine ganglion (synapse) • zygomaticotemporal nerve • lacrimal nerve • lacrimal gland
Sympathetic• Deep petrosal nerve (internal carotid artery (ICA) plexus) • Vidian nerve • pterygopalatine ganglion (passes through WITHOUT synapsing)
LymphaticsPreauricular (parotid) lymph nodes
Oral-exam tip
  • The parasympathetic pathway for lacrimation involves the pterygopalatine ganglion.
  • The preganglionic fibres originate in the superior salivatory nucleus.
  • A lesion at the geniculate ganglion (e.g., herpes zoster oticus) causes ipsilateral reduced lacrimation + facial palsy + hyperacusis.

Accessory Lacrimal Glands

GlandLocationSecretion
• Krause (~42 upper, ~6 lower)• Deep in conjunctival fornix (subconjunctival)• Serous (basal aqueous)
• Wolfring (~3 upper, ~1 lower)• Superior border of upper tarsus • Inferior border of lower tarsus• Serous (basal aqueous)
• Meibomian (~25 upper, ~20 lower)• Within tarsal plates• Lipid layer - prevents tear evaporation
• Goblet cells• Conjunctival epithelium • Highest density: inferior and medial conjunctiva near the fornix• Mucin 5AC (MUC5AC)
• Glands of Moll• Modified apocrine at lid margin near lashes• Modified sweat secretion
• Glands of Zeis• Sebaceous glands at lash follicle• Oily secretion

Tear Film - Classic vs. Modern Model

  • Classic three-layer model described by Wolff (1946): innermost mucin layer → middle aqueous layer → outermost lipid layer.
  • Modern two-phase model (Bron et al., 2004 onward): An outer lipid layer overlies a muco-aqueous phase, which overlies the carbohydrate-rich epithelial glycocalyx.
  • Total tear film thickness ~3–5 µm.
  • Tear volume ~7 µl.
  • Tear turnover ~16%/min.
  • Tear film break-up time (TBUT) ≥10 sec is normal.
  • Fluorescein tear-film break-up time (TBUT) <5 sec, when measured with smaller controlled fluorescein volumes, supports dry eye disease; additional assessment is required to distinguish aqueous-deficient dry eye (ADDE) from evaporative dry eye (EDE).

Excretory (Drainage) System - Detailed Anatomy

The lacrimal drainage system (LDS) runs from proximal to distal: Puncta → Canaliculi → Common Canaliculus → Valve of Rosenmuller → Lacrimal Sac → Nasolacrimal Duct, which opens into the Inferior Meatus at the Valve of Hasner.

Lacrimal Puncta

  • Located on the lacrimal papilla at the medial end of each lid margin; the upper and lower puncta are approximately 5 mm and 6 mm, respectively, from the medial canthal edge.
  • Upper punctum is slightly more medial than the lower punctum.
  • Diameter: ~0.3 mm (range 0.2–0.3 mm). Surrounded by a ring of dense fibrous tissue.
  • Normally directed posteriorly into the tear lake. Correct apposition to the globe is critical for adequate drainage.
  • The punctum opens into a vertical canaliculus approximately 2 mm long, which widens to form the ampulla before turning medially as the horizontal canaliculus.
MCQ Trap
  • The lower canaliculus drains approximately 60% of tears - not 50:50 between upper and lower.

Lacrimal Canaliculi

SegmentLengthDiameterDirection
Vertical segment~2 mm~0.5 mmPerpendicular to lid margin
Horizontal segment~8 mm~0.5 mm (dilates up to ~3-fold)• Parallel to lid margin • Runs medially
Total per canaliculus~10 mm--
  • Wall: Non-keratinised stratified squamous epithelium surrounded by elastic tissue - allows distension during syringing/dilation.
  • In most individuals, upper and lower canaliculi join to form a common canaliculus (~3–5 mm) before entering the sac; separate openings are uncommon.

Valve of Rosenmuller (Lacrimal Valve)

  • A mucosal fold at the common canaliculus–sac junction that facilitates one-way tear flow and limits reflux of sac contents into the canaliculi.
  • Obstruction at the level of the common canaliculus is surgically critical.
  • Standard dacryocystorhinostomy (DCR) bypasses the sac–nasolacrimal duct (NLD) block but cannot overcome a pre-sac (canalicular) block.
Exam pearl
  • For complete common canalicular obstruction without residual patency, bypass surgery - often conjunctivodacryocystorhinostomy (CDCR) with a Jones tube - is preferred; standard dacryocystorhinostomy (DCR) alone does not bypass the proximal obstruction.

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Keep reading Anatomy of the Lacrimal System

8 more sections are included with the Clinical plan.

  • Lacrimal Sac
  • Tear Drainage Mechanism - Lacrimal Pump
  • Clinical Investigations for Lacrimal Assessment
  • Surgical Anatomy for Dacryocystorhinostomy (DCR)
  • Evolving Concepts
  • High-Yield MCQ Traps

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