Quick Facts
The nasolacrimal duct is the duct that conveys the tears from the lacrimal sac into the inferior nasal meatus (Dorland, 2011).
Related parts of the anatomy
Structure and/or Key Feature(s)
The nasolacrimal duct is the inferior continuation of the lacrimal sac. It is approximately 18 mm long and descends to open anteriorly in the inferior meatus of the nasal cavity. A fold of mucosa, the plica lacrimalis, extends over the opening of the nasolacrimal duct (ostium lacrimalis) in the nasal cavity forming a valve (Standring, 2016).
Anatomical Relations
The nasolacrimal duct is contained within an osseous canal formed by the maxilla, lacrimal bone, and inferior nasal concha.
Function
Most of the tear fluid is drained via the nasolacrimal duct. Tears collect at the medial angle of the eye (medial canthus) and two puncta located here open into the superior and inferior lacrimal canaliculi. The canaliculi transport tears to the lacrimal sac, and into the nasolacrimal duct which directs them inferiorly to open the inferior meatus of the nasal cavity. If tear secretion increases, as in crying, the output of the nasolacrimal duct increases, and the tears and mucus can flow out the nostrils (runny nose). If the capacity to drain tears is overwhelmed, they spill over the margin of the lower eyelid and onto the cheek.
References
Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.
Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series 41 edn.: Elsevier Limited.
