Tearing eyes in cats can be caused by a variety of reasons. Here are some common causes:

Foreign body irritation: Dust, hair, or other foreign objects get into the eyes, irritating them and causing tearing.
Eye infections: Bacterial, viral, or parasitic infections can cause conjunctivitis or keratitis, leading to tearing, redness, and swelling of the eyes.
Allergies: Cats may have allergic reactions to food, environmental allergens, or medications, causing eye inflammation and tearing.
Ingrown eyelashes: Eyelashes growing inwards can irritate the eyes and cause tearing.
Other eye problems include glaucoma, cataracts, and abnormal eye structure.