is this hereditory or just a mechanical fault?

Sometimes the tear ducked is just blocked or it can be actually not opened at all.

WHen the teeth sometimes they get sore eyes which then rubbed etc causing a duct problem this certainly would not be hereditary.

WHen it is closed from birth this could be debated like any other deformity at birth :-)

HTH

Dunno if its the same but where I work I have to flush rabbits tear ducts this is from a genetic problem in these particular rabbits.