Table of contents

Principles of the Lacrimal System

The majority of the tear film is secreted by the lacrimal gland. The drainage of these tears is facilitated by the nasolacrimal system.

Disorders of lacrimation lead to either a watery eye or a dry eye.

Anatomy and Physiology

Tear Flow

The lacrimal apparatus. A) lacrimal gland B) Superior punctum C) Superior lacrimal canal D) Lacrimal sac E) Inferior punctum F)Inferior lacrimal canal G)Nasolacrimal canal By Erin Silversmith, CC BY 2.5.

Secretion by the lacrimal gland onto the ocular surface
Channeled medially by the orbicularis pump mechanism
Drainage into the nasolacrimal system via the upper and lower puncta
Flow through the upper and lower canaliculi into the common canaliculus
Common canaliculus → Nasolacrimal sac → Nasolacrimal duct → inferior nasal meatus

Disorders of tearing are caused by an imbalance between secretion and excretion of tears.

Tear Film

There are 3 layers of tear film:

Lipid layer

The thinnest and most superficial layer
Produced by the meibomian gland (Sebaceous).
Prevents evaporation of the tear film.

Aqueous layer

Produced by the lacrimal gland.
Thickest layer
Has an immune function

Mucin layer

Deepest layer
Produced by conjunctival goblet cells.
Spreads the film evenly and keeps it stable on the ocular surface.

Reflex tearing is a common cause of hypersecretion. It is caused by irritation of the ocular surface. A good quality tear film reduces reflex tearing.

Glands of Lacrimation

Lacrimal Gland (main)

Sensory innervation → lacrimal nerve (branch of CNV1)
Lacrimation (secretomotor) → Parasympathetic (CN7)

Accessory Lacrimal Glands

Krause and Wolfring glands are accessory lacrimal glands that maintain a basal aqueous layer
- Krause glands are found at the conjunctival fornices and are more abundant in the upper fornix
- Wolfring glands a less numerous but bigger. They are found at the tarsal plate.

Eyelash Associated Glands

The glands of Moll and Zeis both service eyelash follicles
Moll glands are apocrine (modified sweat glands)
Zeis (and Meibomian glands) are holocrine (sebaceous)

Special Tests

There are a variety of special tests to investigate the lacrimal system. These tests are detailed in the table below.

	Description	Interpretation
Schirmer’s test	Filter paper placed under the lower lid. Amount of moisture measured after 5 mins	>10mm → normal (Schirmer negative) <5mm → tear deficiency (Schirmer positive)
Tear film break-up time	Eye is stained with fluorescein dye and the time taken for the first dry spot to appear on the cornea is measured	<5 seconds → abnormal tear film 10-30 seconds → normal
Jones 1 test	Dye squirted onto the conjunctiva and cotton bud placed in the inferior meatus.	No dye on cotton bud → do jones 2
Jones 2 test	Dye syringed into the nasolacrimal system and cotton bud placed in the inferior meatus.	No dye on cotton bud → nasolacrimal system obstruction Dye is now seen on cotton bud → pump/punctal problem
Dacryocystography	Radiological evaluation using injected fluorescent contrast to evaluate the nasolacrimal system morphology	Excellent anatomical detail for evaluation Invasive and painful
Dacryoscintigraphy	Radiological evaluation of nasolacrimal system drainage using radiopharmaceutical eyedrops	Evaluation of tear flow but provides poor anatomical detail Painless

The Jones tests have been largely superseded by more useful radiological imaging methods such as dacryocystography in clinical practice.