Glaucoma, family of eye diseases characterized by increased pressure within the eye and resulting loss of vision. Although the vision loss caused by glaucoma is irreversible, medication or surgery can usually control the pressure within the eye and slow or halt the progression of the disease. If glaucoma is diagnosed in its early stages, it can be treated effectively, and vision can usually be preserved.

 Glaucoma occurs in two main varieties, known as chronic simple and acute glaucoma. In chronic simple glaucoma, pressure within the eye rises gradually, and vision loss progresses over a period of years. In acute glaucoma, the pressure inside the eye rises suddenly and immediate medical treatment is necessary to preserve vision. Acute glaucoma is also known as narrow-angle or angle-closure glaucoma, because the angle between the cornea (the transparent layer of tissue at the front of the eye) and the iris (the colored part of the eye) becomes smaller than normal. Chronic simple glaucoma is also known as open-angle glaucoma because the angle between the cornea and iris remains normal. This article focuses on chronic simple glaucoma, which accounts for 95 percent of all cases of glaucoma.

 Worldwide, approximately 6.7 million people are blind due to glaucoma, making this condition the second leading cause of blindness. Between 90,000 and 120,000 people in the United States alone have lost significant vision due to glaucoma, and the condition is the leading cause of preventable blindness in the nation. More than two million people are currently being treated for glaucoma, and an estimated one million additional cases of the disease are undiagnosed.