Glaucoma

Glaucoma

Often called the "sneak thief of sight," glaucoma refers to a group of eye diseases that damage the nerves carrying images from the eye to the brain. It is a leading cause of blindness in the U.S., accounting for nine to 12 percent of all blindness, according to Prevent Blindness America. The organization estimates that one in every 30 Americans age 40 and older has the disease, but half don't know it. Glaucoma usually produces no symptoms until the disease has progressed to the point of robbing a person's sight.

Although glaucoma has no cure, it can be controlled and vision maintained if it is caught early. That's why comprehensive eye examinations are recommended at least every two years for those at increased risk for the disease. Although anyone can get glaucoma, the risk is higher for those over age 60, those who have a family history of the condition, and African Americans. The National Eye Institute reports that African Americans are five times more likely than Caucasians to develop glaucoma. The risk of blindness from glaucoma is four times greater in African Americans than Caucasians overall, and 15 times greater in African Americans age 45 to 65 than in Caucasians of the same age, according to the institute.

Additional risk factors include:

• Diabetes
• nearsightedness, called myopia
• regular, long-term steroid or cortisone use
• previous eye injury

Another risk factor for glaucoma is high pressure within the eye. Pressure in the eye is known as intraocular pressure. It's a common misconception that having high intraocular pressure means you're a victim of glaucoma. In fact, you can have high intraocular pressure, known as ocular hypertension, and not have glaucoma. Whether you develop glaucoma depends on how much pressure your optic nerve-the bundle of 1.2 million nerve fibers that transmits images from the eye to the brain-can take without being damaged.

The first step in understanding glaucoma and its relationship to intraocular pressure is learning how the eye works. The outer protective layer of eye includes clear tissue through which light enters the eye, known as the cornea. The iris is the colored part of the eye that contains muscles that make the pupil (the dark-colored area in the center of the eye that lets light into the eye) open and close. Located behind the iris is the lens, a transparent structure with an outward curve on both sides that focuses light onto the retina at the back of the eye. The retina is made of light-sensitive tissue that sends visual messages via nerve impulses to the brain through the optic nerve. The brain then processes the nerve signals into the images you see.

The anterior chamber is a space in the eye bordered by the cornea, iris, pupil and lens. Flowing through this chamber is a liquid, called the aqueous humor, which supplies oxygen and nutrients to the cornea and lens, and helps maintain the shape of the eyeball. A tiny gland, called the ciliary body, located behind the iris produces the fluid. The fluid travels from the gland through the pupil into the anterior chamber, exiting at an angle where the cornea and the iris meet. At the angle is a spongy mesh of tissue that works like a drain, called the trabecular meshwork.