Common causes
Conjunctivitis, corneal ulceration, foreign material, abnormal eyelashes, eyelid disorders, blocked nasolacrimal drainage, and facial anatomy can all cause tearing. Brachycephalic dogs and some short-faced cats may have chronic overflow related to anatomy.
Why color and discomfort matter
Clear tears without discomfort can be less urgent than thick yellow-green discharge, marked redness, or pain. Brown tear staining is caused by pigments in tears and does not by itself diagnose infection.
How the eye is checked
A veterinary eye exam may include fluorescein staining of the cornea, tear-production testing, eyelid and eyelash evaluation, and assessment of tear drainage. Corneal ulcers can worsen rapidly, so painful eyes should not be treated with leftover drops.
Home care
Gently keep the surrounding fur clean and dry, and avoid harsh stain-removal chemicals near the eye. Seek same-day care for squinting, trauma, sudden cloudiness, a protruding eye, or rapid vision change.