For instance, olopatadine (Pataday) is an antihistamine eye drop that works by blocking histamine to relieve itchy, red eyes. But eye drops like ketotifen (Alaway, Zaditor) and alcaftadine (Lastacaft) are considered both antihistamines and mast cell stabilizers. Mast cell stabilizers work by stopping additional histamine release in the eye.

If you have itchy, watery eyes, antihistamine eyedrops may make you feel better. These medicines block histamine in the body. Histamine is a chemical that your immune system makes when you come in contact with an allergy trigger. It causes many of your allergy symptoms. Antihistamine eyedrops can quickly ease your symptoms.