The etiology of congenital nasolacrimal duct obstruction is most commonly a membranous obstruction at the valve of Hasner at the distal end of the nasolacrimal duct. General stenosis of the duct is the second most common cause of duct obstruction. Congenital proximal lacrimal outflow dysgenesis involves maldevelopment of the punctum and canaliculus. Proximal outflow dysgenesis can occur concurrently with distal obstruction. Congenital lacrimal sac mucocele or dacryocystocele occurs when there is a membranous cyst extending from the distal end of the duct into the nose. The nasolacrimal duct sac is filled at birth with clear amniotic fluid.
Congenital nasolacrimal duct obstruction occurs in approximately 5% of normal newborn infants. The blockage occurs most commonly at the valve of Hasner at the distal end of the duct. There is no sex predilection and no genetic predisposition. The blockage can be unilateral or bilateral. The rate of spontaneous resolution is estimated to be 90% within the first year of life. Thus timing intervention with resolution makes this a “winner’s game”.