More than 3 million adult Americans have glaucoma, making it one of the leading causes of blindness in the U.S.
The most common form, chronic open-angle glaucoma, generally appears in middle age and seems to have a genetic component: One in five people with glaucoma has a close relative with the condition. In chronic, open-angle glaucoma, sight begins to fade in the outer areas (peripheral) of the visual field; if untreated, tunnel vision and then blindness follow.
The inside of the eye continuously produces and drains away a fluid called aqueous humor. As fresh aqueous is produced by cells inside the eye, an equal amount must exit through a drainage passageway (trabecular meshwork). If not enough drains away, pressure will increase inside the eye. The effects of intermittent or persistent high pressure on delicate retinal nerve fibers and the optic nerve results in permanent vision loss.
Glaucoma has long been called "the silent thief of sight," because there can be significant damage to the eye before the problem is discovered. Glaucoma damage is irreversible.
Types of Glaucoma
Glaucoma is a collection of diseases, all of which share a common outcome: irreversible damage to delicate nerve fibers and the optic nerve that sends information to the brain. The most common type of glaucoma is called chronic open-angle glaucoma, accounting for about 75%-90% of cases. There are multiple causes of this type of glaucoma. In chronic open-angle glaucoma, both eyes may be affected at the same time, but one eye is often worse than the other.
Narrow or closed-angle glaucoma is less common and occurs suddenly with blurred vision, a great deal of pain in the eye and head, and redness, usually in one eye first. In closed-angle glaucoma, the flow of aqueous is blocked from entering the drainage system, causing a sudden and severe rise in pressure inside the eye. Just like in open-angle glaucoma, the high pressure permanently damages the retinal and optic nerve fibers. Acute closed-angle glaucoma is a medical emergency and needs immediate medical care to restore normal aqueous outflow, reduce pressure, and prevent permanent damage to the eye and blindness.
Congenital glaucoma is rare. It is present in some infants at birth or within the first few years of life. Infants with glaucoma usually have cloudy corneas (the front of the eye) that are sensitive to light, and have excessive tearing. Severe vision loss and even blindness may occur if the problem is not diagnosed and treated early. When a similar type of glaucoma occurs between age 3 and adulthood, it is called juvenile glaucoma.
Secondary glaucoma is a broad category of glaucoma problems usually associated with another eye disease or disorder, such as a very mature cataract, uveitis (inflammation inside the eye), bleeding, eye tumor, or an eye injury. People with diabetes can develop abnormal blood vessels inside the eye, making them susceptible to neovascular glaucoma, a particularly severe form of the disease in which new blood vessels obstruct the flow of aqueous fluid from the eye.
SOURCES: American Glaucoma Society. Weinreb, R. Lancet, 2004. Curcio, C. Journal of Comparative Neurology, Oct. 1, 1990. American Academy of Ophthalmology. Glaucoma Research Foundation. U.S. Preventive Services Task force: "Screening for Primary Open-Angle Glaucoma in the Primary Care Setting." Mayo Clinic. Distelhorst, J. American Family Physician, May 1, 2003.