Nasolacrimal duct

At a glance

English

Nasolacrimal duct

Latin (TA2)

Ductus nasolacrimalis

System

Eye

Region

Head

Side

Paired, left and right

About the nasolacrimal duct

The nasolacrimal duct is the final part of the tear drainage pathway. It leads on from the lower end of the lacrimal sac at the medial corner of the orbit and runs through the nasolacrimal canal, a bony channel formed by the maxilla, the lacrimal bone and the inferior nasal concha. It is about eighteen millimetres long and is directed downwards, slightly backwards and a little outwards, so that it lies roughly along a line from the medial angle of the eye to the first molar region.

Its lower end opens beneath the inferior nasal concha, in the front part of the inferior meatus of the nasal cavity. The opening is often slit-like and partly guarded by a fold of mucous membrane, the lacrimal fold or valve of Hasner, which helps stop air and mucus being forced up into the sac when the nose is blown. Smaller mucosal folds may be found higher up the duct. Its lining, like the sac, is a columnar epithelium with goblet cells over a layer of connective tissue rich in veins.

Tears made by the lacrimal gland are spread over the eye and then drained through the puncta, canaliculi and sac into this duct. That is why crying, or watering from an allergy, makes the nose run, and why eye drops can sometimes be tasted. Pressing gently on the inner corner of the closed eye after putting in drops slows this drainage and keeps more of the medicine on the eye and less in the bloodstream.

Blockage of the duct causes overflow of tears onto the cheek, called epiphora, and can lead to infection of the sac. In newborns the lower end is frequently still closed by a membrane; most open in the first year, sometimes after massage or probing. A cystic swelling of the duct at birth is a dacryocystocele. Swelling of the nasal lining in colds or allergy may narrow the outlet for a time.

Function and supply

Begins at

Begins at the lower end of the lacrimal sac at the upper opening of the nasolacrimal canal.

Ends at

Opens into the inferior nasal meatus beneath the inferior nasal concha, partly covered by the lacrimal fold.

Function

Conveys tears from the lacrimal sac into the nasal cavity, where they are evaporated or swallowed.

Nerve supply

Sensory fibres from the anterior superior alveolar nerve and branches of the infratrochlear nerve.

Blood supply

Branches of the sphenopalatine and infraorbital arteries and the angular artery; veins form a cavernous plexus around the duct draining to the nasal veins.