Lacrimal canaliculus

At a glance

English

Lacrimal canaliculus

Latin (TA2)

Canaliculus lacrimalis

System

Eye

Region

Head

Side

Paired, left and right

About the lacrimal canaliculus

Tears that have washed across the front of the eye gather at the medial angle in a small pool, the lacrimal lake. From there they enter two narrow passages, one in the upper and one in the lower eyelid, called the lacrimal canaliculi. These are the first part of the drainage pathway that ends in the nose, followed by the lacrimal sac and the nasolacrimal duct. Each canaliculus is about ten millimetres long and well under a millimetre wide.

Each canaliculus begins at a punctum, a pinhole opening on the summit of the lacrimal papilla near the inner end of the lid margin. It then runs for about two millimetres at right angles to the margin, upwards in the upper lid and downwards in the lower, before turning sharply towards the nose. The corner is slightly widened into an ampulla. The horizontal parts run medially, close to the lid margins, and in most people the upper and lower channels join to form a short common canaliculus that pierces the lateral wall of the sac. The upper canaliculus is a little shorter and narrower than the lower, which drains most of the tear flow.

The wall is lined by non-keratinised stratified squamous epithelium on a very elastic lamina propria, so the passage can be dilated. Outside it lie fibres of the lacrimal part of orbicularis oculi. When the lids close, this muscle compresses and shortens the canaliculi and drives tears towards the sac; when they open, the elastic recoil draws fluid in. Blinking therefore acts as a pump.

Clinically the canaliculi can be torn in lid injuries near the medial angle and need careful repair to avoid permanent watering. Inflammation of the channel, canaliculitis, often from slow-growing bacteria, causes a swollen punctum and discharge. Narrowing or blockage gives an overflow of tears (epiphora), and in dry eye the puncta may deliberately be closed with small plugs to keep tears on the eye.

Function and supply

Begins at

Begins at the lacrimal punctum on the lacrimal papilla of the upper or lower eyelid.

Ends at

Ends in the sac's lateral wall, usually after joining its partner as a common canaliculus.

Function

Conducts tears from the lacrimal lake to the lacrimal sac, aided by the pumping action of orbicularis oculi during blinking.

Nerve supply

Sensory supply from the infratrochlear nerve; the surrounding orbicularis fibres are supplied by the facial nerve.

Blood supply

Medial palpebral branches of the ophthalmic artery.