Tears rinse debris from the eye and are drained into the nose through two small pores (lacrimal puncta) in the inner corner of the upper and lower eyelid.
Each punctum leads to a horizontal drainage channel (lacrimal canaliculi), which leads to a drain bag deep under the skin on the medial angle of the eye (lacrimal sac).
Finally, this sac drains tears down (via the nasolacrimal duct) into the nose as shown in the following image. This is the reason why you may experience a runny nose when crying.
What happens when there is a stenosis of the lacrimal duct?
Any narrowing, disorder or blockage of the eyes’ drainage system may result in damp or watery eyes, either under specific conditions (as for instance in the cold) or more regularly.
Lacrimation is referred to as “epiphora”. Often, a stenosis at the nasolacrimal duct can also result in enlargement of the lacrimal sac. This may cause accumulation of mucus in the sac, which may either flow back onto the surface of the eye (causing macular vision, ‘sticky’ eyelids, or repeated eye infections), or may cause the infection of the lacrimal sac itself (a condition referred to as dacryocystitis).