Relative roles of upper and lower lacrimal canaliculi in normal tear drainage.

A total of 88 cases of impaction of the eyelash into the lacrimal punctum were collected from 34,256 outpatients, and 39 cases of lash impaction into the Meibomian gland duct were found among 30,456 outpatients. Observations of these patients were analyzed to find the relative roles of the upper and lower lacrimal canaliculi in the normal tear drainage. In the cases of the Meibomian gland duct, the impaction occurred at a similar incidence in the upper and lower eyelids. However, in the cases of the punctum, the upper punctum was affected about three times more frequently than the lower punctum. The impaction of the eyelashes probably occurred at about the same rate in both puncta, but the present results suggested that the lashes in the lower punctum disappeared more easily into the drainage system than the lashes in the upper punctum. The lower canaliculus should, therefore, play the major role in normal tear drainage.