Glaucoma is a collection of eye disorders that cause damage to the optic nerve, which is essential for proper vision. This injury is typically caused by an extremely high pressure in your eye. For those over the age of 60, glaucoma is one of the major causes of blindness. The three main types of glaucoma are open-angle, angle-closure, and congenital glaucoma. Open-angle glaucoma (OAG) is the most common type of glaucoma and it occurs when fluid builds up within the eyeball, causing pressure to increase above normal levels. This increased pressure damages the optic nerve, resulting in loss of visual function until surgery can reduce this pressure or new blood vessels grow into the optic disc, providing relief from some of the pain and blindness associated with OAG. Angle-closure glaucoma occurs when the lens of the eye prevents fluid from draining out, which causes pressure to rise. In severe cases, this pressure may cause the iris to collapse upon the front of the eye, blocking the source of light and preventing any vision at all. This type of glaucoma requires emergency medical attention because if left untreated it can lead to permanent blindness. Congenital glaucoma is present at birth and cannot be treated successfully with medication, so the eye will need to be surgically removed to prevent further damage.