Tränenbahn

Tränenbahn, in human anatomy the lacrimal drainage system, is the part of the lacrimal apparatus responsible for removing tears from the ocular surface and delivering them to the nasal cavity. It comprises the puncta lacrimalia, the canaliculi, the lacrimal sac, and the nasolacrimal duct.

The puncta are two tiny openings at the medial margins of the upper and lower eyelids that collect tears. Tears flow through the canaliculi into the lacrimal sac, which sits in the lacrimal fossa. From there, the nasolacrimal duct descends and opens into the inferior meatus of the nasal cavity. The adults have valves including the valve of Rosenmüller at the canalicular end and the valve of Hasner at the distal ductal end, which help regulate flow and prevent reflux.

Drainage is driven by blinking and the pressure changes produced by eyelid movement; tear production by the lacrimal glands continuously replenishes the tear film, which consists of lipid, aqueous, and mucin layers that protect and lubricate the ocular surface.

Clinical relevance: obstruction of the lacrimal drainage system can cause epiphora (excess tearing) and dacryocystitis. Congenital nasolacrimal duct obstruction is common in infants. Diagnosis may involve dacryocystography or irrigation tests, and treatment ranges from probing and intubation to dacryocystorhinostomy (DCR), performed externally or endonasally.