Glaucoma is caused by increased intraocular pressure in the eye. The optic nerve, which is responsible for carrying all visual information to the brain, is damaged by increased pressure, and the damage is irreparable.
The most common form is called open-angle glaucoma, which represents about 90% of all cases. In this case, the condition is painless and begins by affecting vision on the periphery of the visual field. The other 10% of cases are caused by closed-angle glaucoma, which occurs suddenly with extreme pain, visual disturbances like lights and halos, and nausea and vomiting. Closed angle glaucoma is a real emergency and must be treated in the emergency room to prevent permanent blindness. People of East Asian descent are at the highest risk for developing closed angle glaucoma.