Common duct enters the sac at the fundus 3.5mm below the apex
The sac is separated from the middle meatus of the nasal cavity via the lacrimal bone and frontal process of the maxilla.
opening of the duct in the inferior meatus is protected by a mucosal fold, known as the valve of Hasner, whose function is to prevent air and other nasal contents from entering, especially when the nose is blown.
with blinking, the superior and deep heads (Horner’s muscle) of the orbicularis contract forcing the puncta to move medially, the canaliculi to shorten and compression of the lumen of the canaliculi.
contraction of the deep heads of the pre-septal portion causes the nasolacrimal sac to expand. The resultant negative pressure allows the tears to flow from the common canaliculus into the sac.
On eyelid opening, the canaliculi expand and lengthen and the sac collapses following relaxation of the orbicularis muscles. Positive pressure is now induced, forcing the tears to flow down the nasolacrimal duct into the nose
Epiphora due to lacrimal hypersecretion is never an indication for surgery on the lacrimal excretory system.
Resection of the lacrimal gland or severance of its ducts or efferent nerve supply to decrease secretion is condemned because of the risk of keratitis sicca.
Many authors contend that the superior canaliculus is of little or no importance in tear drainage, and repair of an injury to the upper canaliculus is unnecessary
Surgical Punctal repositioning (if has medial ectropion)
Canaliculaplasty - strictures of the punctum
Externalizing the residual lower canaliculus in an -ostomy-type procedure -possible even when the residual canaliculus is only one-fourth of the normal canalicular length
moving the fundus of the tear sac anteriorly and approximating it to the conjunctiva disrupts the lacrimal pump mechanism and often ends in failure.
approach may be external or endoscopic (usually with laser)
Endoscopic laser method
Dilatation of the lower punctum was performed and a 20G vitreoretinal probe was inserted in the lower canaliculus and advanced into the nasolacrimal sac. The light was directly visualised endonasally with a 0° rigid nasal endoscope, and the laser energy was delivered
The nasal mucosa and lacrimal bone were ablated and the ostium was enlarged anteriory as necessary with a microronguer.