How do tears exit?

The mechanisms of tear flow, blinking, and tear drainage were studied employing high speed slit-lamp cinematography using a polystyrene microsphere suspension as a tracer of tear movement. It was demonstrated that: (1) Tears are drawn into the canaliculi during the relaxation phase of blinking. (2) Both superior and inferior puncta function as normal tear drainage routes. (3) The superior punctum alone is sufficient to handle tear drainage. (4) There is some regurgitation of tears from the canaliculi. (5) An intact blink mechanism is necessary for effective tear drainage. (6) There is an actual closure of the puncta during blinking. This is sufficient to effect tear exit without the lids meeting. The clinical impression that in order to effectively prevent tear drainage in the treatment of dry eyes, it is necessary to occlude both the superior and inferior puncta was confirmed.