Epiphora is often a multifactorial problem. Tearing, as a symptom, results from an imbalance between tear production and tear clearance. This is complicated by the fact that tear production is not constant and tear clearance depends on evaporation from the ocular surface in combination with drainage through the efferent lacrimal system.

Tears are produced in two ways — at a very low basal rate and as a reflex to any irritation on the surface of the eye. Basal tear secretion occurs largely from the accessory lacrimal glands and the conjunctival epithelium and occurs at a minimal rate. Reflexive tears are produced mostly from the lacrimal gland and can be made at a rate up to 100 times greater than is basal tear secretion.

An imbalance in the system in either direction leads to epiphora. Tear production in excess of tear loss (as seen in obstructions in the efferent lacrimal system or, rarely, in primary overproduction syndromes) directly leads to tearing. Tear loss in excess of production causes reflexive tearing, which may indirectly lead to tearing. History and examination therefore is focused on determining what factors are contributing to the epiphora.