Nasolacrimalduct

The nasolacrimal duct is a component of the tear drainage system that carries lacrimal fluid from the lacrimal sac into the nasal cavity. Tears produced by the lacrimal glands wash over the ocular surface and drain through the puncta, across the Lacrimal canaliculi, into the lacrimal sac, and from there through the nasolacrimal duct to the inferior meatus of the nasal cavity. The process is aided by blinking and a coordinated lacrimal pump mechanism.

Anatomy and course: the nasolacrimal duct extends from the lacrimal sac in the medial orbit, traversing the lacrimal bone and maxilla, and opens into the inferior meatus of the nasal cavity. The distal end is guarded by the valve of Hasner, which helps prevent reflux of nasal contents into the duct. The duct is part of a continuous passage from the ocular surface to the nasal cavity and is closely related to the surrounding sinus and nasal structures.

Development and variation: the duct develops from the nasolacrimal groove between the developing eye and nose and becomes patent through canalization during fetal life. Obstruction can be congenital or acquired. Congenital nasolacrimal duct obstruction results from persistence of a membrane at the distal ostium (Hasner valve) and is the most common cause of neonatal tearing.

Clinical significance: obstruction of the nasolacrimal duct causes epiphora and mucopurulent discharge. In infants, many cases resolve spontaneously with simple lacrimal sac massage and good hygiene; persistent obstruction may require probing, intubation, or surgical procedures such as dacryocystorhinostomy in adults. Infection of the lacrimal sac (dacryocystitis) can occur if drainage is blocked.