ALPHAGAN Z contains Brimonidine which are Antiglaucoma agents. These are sterile, preserved, aqueous solution works by reducing pressure within the eyeball. It is used to treat the conditions of glaucoma or ocular hypertension (pressure in the eye). Glaucoma is a condition which damages the optic nerve, the health of which is vital for good vision. It is often caused by an abnormally high pressure in your eye. Ocular hypertension is a condition where the pressure inside the eye is higher than normal. In this condition the front of the eye does not drain aqueous humor (fluid in the eye) properly which causes eye pressure to build up.