The term "functional obstruction" is confusing and should be avoided. Patients with tearing whose lacrimal drainage passages are patent to syringing may have an incomplete anatomic obstruction that can be demonstrated by intubation dacryocystography with subtraction. Alternatively, they may have anatomically normal lacrimal passages but a physiologic dysfunction that can be demonstrated by nuclear scintillography, with computer assistance when the abnormality is subtle; in this case the problem is usually of the eyelids, punctum or lacrimal pump, though in rare cases a lacrimal sac that drains poorly is at fault.