Causes
Narrow or blocked tear ducts (common in small breeds), abnormal eyelids or eyelashes, or excess tear production due to irritation. Brachycephalic breeds are predisposed.
Diagnosis
Ophthalmological examination to rule out treatable causes (abnormal eyelashes, blocked ducts, irritation).
Treatment
It depends on the cause: daily cleaning of the area, treating the cause if it is correctable (eyelashes, conjunctivitis). In many small breeds it is a chronic trait that is only managed with hygiene.
Prevention
Daily cleaning of the area below the eye, and treating the causes of eye irritation.

