Intraocular pressure (IOP) is the fluid pressure inside the eye. The front half of the eye is filled with a clear fluid known as the “aqueous humor”. This fluid is continuously produced and constantly flows in and within the eye, maintaining normal pressure inside the eye. If there is either reduced drainage or excessive production of this fluid, the pressure in the eye will increase. This increased eye pressure if left untreated can damage the eye (optic) nerve leading to glaucoma and can cause irreversible vision loss.