Adnexa · 22 of 24
What is the lacrimal drainage system?
Tears leave the eye through two tiny openings at the inner ends of the lid margins, the puncta, and run through the canaliculi to the lacrimal sac in a groove at the inner corner of the orbit, then down the nasolacrimal duct into the nose beneath the inferior turbinate. That is why crying makes the nose run, and why a blocked duct makes an eye water.
- Puncta
- One on each lid, about 6 mm from the inner canthus, facing backwards into the tear lake
- Canaliculi
- About 2 mm vertical then 8 mm horizontal, joining into a common canaliculus
- Sac
- About 12 mm long, in the lacrimal fossa between the anterior and posterior lacrimal crests
- Duct
- About 12 mm through the bone to the inferior meatus of the nose
The lacrimal pump
Tears do not just drain by gravity. Each blink squeezes the canaliculi and the orbicularis fibres around the sac open it, drawing tears in; when the lids open the sac collapses and pushes them down the duct. A lower lid that has fallen away from the eye or a weak orbicularis, as in a facial palsy, breaks the pump, and the eye waters with nothing blocked at all.
The watery eye and the infected sac
A watery eye in an adult is usually a nasolacrimal duct that has narrowed with age, more often in women; syringing through the punctum finds the block and a dacryocystorhinostomy makes a new opening from the sac into the nose. In a baby the duct's lower end is often still membrane-covered at birth, and it opens by itself in the first year in most, helped by massage over the sac. A blocked duct lets the sac fill and infect: acute dacryocystitis is a hot red painful swelling below the medial canthal tendon, treated with antibiotics and then surgery to prevent it recurring.
The canaliculi are cut by lacerations of the inner lid, and any laceration through the medial lid margin is examined for them, because a missed cut canaliculus means a lifetime of watering.
Examine it
Obstruction means a watery eye; infection of the sac is dacryocystitis.
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