When the lower part of the tear duct is obstructed, we can use tools to unblock the obstruction like a sewer, and then place a tear duct inside the tear duct for a period of time to prevent the tear duct from scarring and becoming obstructed again. However, in some patients with severe obstruction of the tear duct and limited success in unblocking the original channel, we may consider bypassing the diseased portion and cutting out a new channel (see new channel in the picture below). There are two ways to accomplish this, one is to make an incision in the skin surface of the corner of the eye and then locate the lacrimal sac and anastomose it to the mucosa of the nasal cavity, which we call an external lacrimal sac nasolacrimal anastomosis, and the other is to make an incision inside the nasal cavity and reverse past the nasal cavity to locate the lacrimal sac so that the two can be connected, i.e., a transnasal lacrimal sac nasolacrimal stoma.