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The opening of the nasolacrimal duct into the inferior nasal meatus of the nasal cavity is partially covered by a mucosal fold (valve of Hasner or plica lacrimalis). [3] Excess tears flow through the nasolacrimal duct which drains into the inferior nasal meatus.
The lacrimal sac or lachrymal sac [1] is the upper dilated end of the nasolacrimal duct, [2] and is lodged in a deep groove formed by the lacrimal bone and frontal process of the maxilla. It connects the lacrimal canaliculi , which drain tears from the eye's surface, and the nasolacrimal duct , which conveys this fluid into the nasal cavity. [ 3 ]
Nasolacrimal duct obstruction is the obstruction of the nasolacrimal ducts (better known as the tear ducts) and may be either congenital or acquired. Obstruction of the nasolacrimal ducts leads to the excess overflow of tears called epiphora .
From the nasal cavity its continuity with the conjunctiva may be traced, through the nasolacrimal and lacrimal ducts; and with the frontal, ethmoidal, sphenoidal, and maxillary sinuses, through the several openings in the nasal meatuses. The mucous membrane is thickest, and most vascular, over the nasal conchae.
The fluid then flows through the nasolacrimal duct and into the nasopharynx. This drainage results in what is commonly referred to a runny nose during excessive crying or tear production. Injury or fracture of the lacrimal bone can result in posttraumatic obstruction of the lacrimal pathways. [1] [2]
On the nasal surface of the body of the maxilla, in front of the opening of the sinus is a deep groove, the lacrimal groove (or lacrimal sulcus), which is converted into the nasolacrimal canal, by the lacrimal bone and inferior nasal concha; this canal opens into the inferior meatus of the nose and transmits the nasolacrimal duct.
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A smooth, more deeply concave depression on the lacrimal bone, which forms the medial wall of the orbital cavity, in which the lacrimal sac that drains into the nasolacrimal duct is located, is referred to as the lacrimal fossa (or fossa for the lacrimal sac).