Nasolacrimal duct

The nasolacrimal duct (also called tear duct, latin: ductus nasolacrimalis) is a channel that is directly continuous with the lacrimal sac and opens into the nasal cavity, forming the final part of the tear drainage system of the lacrimal apparatus.

Structure of the nasolacrimal duct

The nasolacrimal duct is about 1.2 to 2.4 cm long. It passes through the nasolacrimal canal, which is formed by the lacrimal bone, maxilla, and inferior nasal concha, and opens into the inferior nasal meatus of the nasal cavity with an opening - the aperture of the nasolacrimal duct. The aperture is located beneath the inferior nasal concha and provided with a flap-like mucosal fold that partly covers it called the lacrimal fold, also known as the valve of Hasner.

The membranous wall of the nasolacrimal duct consists of connective tissue and stratified columnar epithelium. The flattened lumen of the nasolacrimal duct is lined by a mucous membrane containing two or more layers of columnar epithelium that has cilia at some sites and also contains mucous-secreting goblet cells.

The nasolacrimal duct drains excess tears from the nasolacrimal sac into the nasal cavity, which explains the phenomenon of a running nose when a person is crying.

Vasculature and innervation of the nasolacrimal duct

The nasolacrimal duct receives blood from the branches of:

  • The medial palpebral artery from the ophthalmic artery
  • The facial artery
  • The infraorbital artery from the maxillary artery
  • The sphenopalatine arteries from the maxillary artery

The nasolacrimal duct is innervated by the infratrochlear nerve from the ophthalmic division of the trigeminal nerve (CN V) and by the anterior superior alveolar nerve from the maxillary division of the trigeminal nerve.