Glaucoma is a group of eye diseases in which the optic nerve, which connects your eye to your brain, is damaged by the pressure of fluid inside your eye. There are two main types of glaucoma. One is primary open-angle glaucoma and the other is angle-closure glaucoma. These types of glaucoma are marked by an increase of intraocular pressure, or pressure inside of the eye. Secondary glaucoma refers to any case in which another disease contributes to or causes increased eye pressure.