Glaucoma is an eye disease that may cause loss of vision. It occurs as a result of a buildup of fluid in the eyeball. The fluid nourishes your eye and keeps it healthy. After the fluid circulates, it empties through a drain in the front of your eye. In people with glaucoma, the drain in the eye is blocked and the fluid can't run out of the eyeball. Instead, the fluid builds up and causes increased pressure in the eye.

Glaucoma can be divided roughly into two main categories, "open angle" or chronic glaucoma and "closed angle" or acute glaucoma. Angle closure, acute glaucoma appears suddenly and often with painful side effects and so is usually diagnosed quickly, although damage and loss of vision can also occur very suddenly. Open angle, chronic glaucoma tends to progress more slowly and so the patient may not notice it until the disease has progressed quite significantly.

Most people who have glaucoma don't have any symptoms. You might not realize that you're losing vision until it's too late. Half of all people with loss of vision caused by glaucoma are not aware they have the disease. By the time they notice loss of vision, the eye damage is severe. Rarely, an individual will have an acute (sudden or short-term) attack of glaucoma. In these cases, the eye becomes red and extremely painful. Nausea, vomiting and blurred vision may also occur.

Worldwide, it is the second leading cause of blindness. Glaucoma affects one in two hundred people aged fifty and younger, and one in ten over the age of eighty. If the condition is detected early enough it is possible to arrest the development or slow the progression with medical and surgical means.