Alphagan is used to treat open-angle glaucoma or high fluid pressure in the eye. Lowering high fluid pressure in the eye reduces the risk of vision loss nerve damage or blindness. This medication lowers pressure by allowing better fluid drainage from within the eye and also by reducing the amount of fluid formed in the eye. It is known as an alpha agonist. This drug is not recommended for use in children less than 2 years of age due to an increased risk of serious side effects such as very slowed breathing. Ask the doctor or pharmacist for details.