Definition:
The nasolacrimal duct is a membranous tube that conveys tears from the eye to the nasal cavity.
Overview:
The nasolacrimal duct is part of the human lacrimal drainage system, responsible for transporting excess tears from the ocular surface to the nasal cavity. Tears are produced by the lacrimal glands and spread across the eye with each blink. They collect in the lacrimal lake near the medial canthus and enter the lacrimal puncta—small openings on the upper and lower eyelids. From there, tears drain through the lacrimal canaliculi into the lacrimal sac, and subsequently flow down the nasolacrimal duct, which terminates in the inferior meatus of the nasal cavity. This anatomical connection explains the phenomenon of a runny nose during crying, also known as epiphora when excessive.
Etymology/Origin:
The term "nasolacrimal" is derived from the Latin words "nasus," meaning nose, and "lacrima," meaning tear, indicating its function as a conduit between the eye and the nose. "Duct" comes from the Latin "ducere," meaning to lead or conduct, describing a tubular structure that transports bodily fluids.
Characteristics:
The nasolacrimal duct is approximately 12–18 mm long and 3–4 mm in diameter in adults. It descends from the lacrimal sac through a bony canal formed by the maxilla, inferior nasal concha, and lacrimal bone. The distal end is typically equipped with a valve-like structure known as Hasner’s valve (or the plica lacrimalis), which prevents the backflow of nasal secretions into the tear drainage system. The duct is lined with respiratory or pseudostratified columnar epithelium and contains goblet cells that contribute to mucus production.
Obstruction of the nasolacrimal duct can lead to epiphora (excessive tearing), recurrent infections such as dacryocystitis, or congenital blockages in infants (commonly due to the failure of Hasner’s valve to open at birth).
Related Topics:
- Lacrimal apparatus
- Dacryocystitis
- Epiphora
- Hasner’s valve
- Lacrimal sac
- Lacrimal canaliculi
- Tears (lacrimation)