The exact cause of glaucoma is unknown, though some experts believe that inner pressure in the eye is the cause. Some people with normal intraocular pressure, though, develop glaucoma. There are several different precursors to glaucoma, but no single determining factor, although there are treatments to slow its progress.
There are four main types of glaucoma: open- and closed-angle glaucoma, congenital glaucoma, infantile glaucoma, and secondary glaucoma.
Open-angle glaucoma occurs when intraocular pressure builds up because fluids fail to drain from the eye normally. This additional pressure inside the eye may damage the nerves and lead to blindness, but not every case of open-angle glaucoma has excessive intraocular pressure.
Closed-angle glaucoma occurs when the eye's drainage angle is blocked. The blockage creates increased intraocular pressure and nerve damage. There are three reasons for this. The iris and lens can be incorrectly positioned and block fluids from moving normally inside the eye chambers. If the iris is damaged, it can fall forward and block the drainage system. Following illness or injury, scar tissue can form between the cornea and iris and block the drainage system.
Secondary causes are also suspect in cases of glaucoma. It can be caused by an injury to the eye, following eye surgery, after a cataract forms, or after certain medications are administered, such as corticosteroids.