“There are several types of glaucoma. The two main types are open-angle and angle-closure. These are marked by an increase of intraocular pressure (IOP), or pressure inside the eye.  The most common type in the United States is called open-angle glaucoma — that’s what most people mean when they talk about glaucoma. The drainage angle formed by the cornea and iris remains open, but the trabecular meshwork is partially blocked. This causes pressure in the eye to gradually increase. This pressure damages the optic nerve. ”

Glaucoma Research Foundation (www.glaucoma.org)