FIGURE 9.1 The anatomy of the human eye. (Drawing by Roberto Osti.)

sure. One percent of people age 60 have POAG, while more than 9 percent of people over 80 develop the disease. For African Americans the figure rises to 10 percent and is up to 25 percent among Caribbean people of African origin (who are less racially mixed than their American counterparts).

The third risk factor, elevated intraocular pressure, results from blockage in the flow of fluid that helps the eye maintain its rigid shape (see Figure 9.1). Normally this clear fluid, called the aqueous humor, circulates between the front of the lens and the back of the cornea. In people with elevated intraocular pressure the outflow of fluid from the anterior chamber of the eye becomes restricted, causing pressure to build up like water behind a dam. Increased pressure in the eye contributes to glaucoma by decreasing the flow of nutrients to the optic nerve, scientists suspect. Because elevated intraocular pressure is the only significant risk fac-