nasolacrimal duct obstruction nasolacrimal duct obstruction nasolacrimal duct obstruction is the obstruction of the nasolacrimal duct and may be either congenital or acquired. obstruction of the nasolacrimal duct leads to the excess overflow of tears called epiphora. nasolacrimal duct obstructionother namesdacryocystitistear system consists of lacrimal gland (a), punctums (b,e), canalicules (c,f), lacrimal sac (d). tear is then drained through nasolacrimal duct (g) into nasal cavityspecialtyophthalmologydifferential diagnosistears arising from lacrimal sac fistula.