Lacrimal sac

At a glance

English

Lacrimal sac

Latin (TA2)

Saccus lacrimalis

System

Eye

Region

Head

Side

Paired, left and right

About the lacrimal sac

The lacrimal sac is the expanded top of the tear duct system. It occupies the lacrimal fossa, a groove on the medial wall of the orbit made in front by the frontal process of the maxilla and behind by the lacrimal bone, between the anterior and posterior lacrimal crests. It is an oval pouch about twelve to fifteen millimetres long. Its upper end, the fundus, is blind and rounded and rises a little above the medial palpebral ligament; its lower end narrows into the nasolacrimal duct, which descends to the nose.

Tears arrive from the eye through the upper and lower lacrimal canaliculi, which usually unite and open into the lateral wall of the sac. In front, the sac is covered by a fibrous extension of the medial palpebral ligament, and the angular vein runs on the skin surface just medial to it. Behind it, the lacrimal part of orbicularis oculi passes to attach to the posterior lacrimal crest. Its lining, like that of the nasolacrimal duct, is a columnar epithelium in two or more layers with mucus-secreting goblet cells, set on loose connective tissue.

The sac is more than a passive tube. With each blink the orbicularis fibres around it alternately widen and compress it, which draws fluid in from the canaliculi and then pushes it down into the duct. It also holds a small store of tears at times of increased flow, and its secretions help trap debris and microbes washed from the eye.

When the duct below is obstructed, tears stagnate and the sac can become infected, producing dacryocystitis: a tender swelling below the medial palpebral ligament, sometimes with pus expressed from the puncta. In infants a blocked lower duct is common and often opens by itself. Contrast injected into the canaliculi and imaged by X-ray (dacryocystography) outlines the sac, and a dacryocystorhinostomy creates a new opening from the sac directly into the nasal cavity.

Function and supply

Begins at

Receives tears from the lacrimal canaliculi, usually through a common canaliculus entering its lateral wall.

Ends at

Continues below into the nasolacrimal duct at the upper opening of the nasolacrimal canal.

Function

Collects tears from the canaliculi and, pumped by orbicularis oculi, passes them into the nasolacrimal duct.

Nerve supply

Sensory fibres from the infratrochlear nerve, with a contribution from the anterior superior alveolar nerve to its lower part.

Blood supply

Branches of the palpebral and dorsal nasal arteries from the ophthalmic artery, the angular artery and the infraorbital artery; veins drain to the angular and infraorbital veins and the nasal venous plexus.