The second leading treatable cause of blindness in the United States, glaucoma is a condition in which deterioration of the optic nerve leads to progressive loss of field of vision. Worldwide, glaucoma is among the top three causes of blindness.
In the United States, about 2.3 million people age 40 years and older have glaucoma. Because the most common form of the condition—open-angle glaucoma—does not cause symptoms in its early stages, about 50 percent of those with glaucoma do not realize they have it.
The risk of glaucoma varies with race and age. The condition is four times more common in Hispanics and five times more common in blacks than in whites, and it occurs more frequently with increasing age. According to data from the National Eye Institute, the prevalence of glaucoma is less than 1 percent in people age 40 to 49. By age 70, it is nearly 3 percent; by age 80, nearly 8 percent.
Two main forms of glaucoma exist:
• Open-angle glaucoma progresses slowly and produces no obvious symptoms until its late stages. It is equally common in men and women and is responsible for about 90 percent of glaucoma cases.
• Angle-closure, or closed-angle, glaucoma is responsible for most of the remaining 10 percent of glaucoma cases. It occurs more often in people of Asian descent. Women are at greater risk than men, as are people who are farsighted.
Both types of glaucoma can lead to blindness, which is caused by damage to the optic nerve.
Many people with glaucoma have intraocular pressure (IOP) that is too high for the optic nerve to tolerate. Susceptibility to high IOP varies from person to person, and risk factors other than IOP also play a role in the development of glaucoma. Early detection and treatment of elevated IOP levels, however, can help prevent damage to the optic nerve.
About 50 percent of people with glaucoma in North America have elevated IOP levels. Interestingly, however, people with normal IOP levels also can suffer damage to the optic nerve. Some researchers believe these individuals have extremely pressure-sensitive optic nerves. Other researchers hypothesize that different factors, such as compromised blood circulation, may damage the optic nerve.