What are the types of glaucoma?

Take Home Points

There will soon be 80 million persons in the world with some form of glaucoma. This estimate is based on surveys that examined thousands of randomly selected adults in nearly every continent. Research at our Glaucoma Center of Excellence shows the total number with glaucoma will increase due to that fact that the proportion of older people in the population is increasing compared to younger people, and glaucoma is more likely to occur in older people. Glaucoma is the second leading cause of blindness worldwide.

There are several forms of glaucoma, and the two most common forms increase with older age. At 40 years old, less than one in 100 persons have glaucoma, while over age 80, nearly one in ten is affected. These rates are different depending upon ethnic derivation and other factors. For example, African-Americans have four times more open angle glaucoma than persons who are European-derived. For angle closure glaucoma, Asians have four times more than either European- or African-derived persons.

Of those with glaucoma, the majority (about two-thirds) have the form called open angle glaucoma. In the United States alone, there are estimated to be 2.5 million adults with open angle glaucoma, about 500,000 with angle closure glaucoma, and another 5-10 million persons who are potential glaucoma patients (glaucoma suspects) due to various kinds of risk factors. Risk factors are features of their eyes or other attributes that make glaucoma more likely to develop.

Both major types of glaucoma have the word "angle" in their name. The angle is a circular zone on the inside part of the eye where the cornea, the clear front wall of the eye, meets the iris, the blue or brown part of the eye. This angle area runs all around the part of the eye where the white sclera and the colored iris meet. In general, an individual either has an open angle or a narrow to closed angle (Figure 6). This is determined by the examination called gonioscopy (see section What tests are needed to diagnose glaucoma?).

Imaging the angle
Figure 6: Imaging the angle. A slice through the front of two eyes taken with a special camera shows an open angle above and a closed angle below (images made with anterior segment optical coherence tomography). The arrow points to where the iris is separate from the cornea in the open angle (upper picture). In the lower picture, the iris is so close to the cornea that it nearly touches the trabecular meshwork (in front of arrowhead).

The aqueous humor fluid nourishes the eye, circulates from back to front, and maintains the eye pressure. Fluid normally moves from where it is produced, the ciliary body, between the lens and the back of the iris, through the round, black opening in the iris called the pupil and leaves the eye at the trabecular meshwork in the angle. Just at the base of the meshwork, fluid can also move out through a second pathway called the uveoscleral outflow. In most eyes, fluid gets to the angle from the back of the eye easily, and these are open angle eyes. In a few eyes, the parts of the eye in the front are too crowded together, and the colored iris can get close enough to block the angle at the meshwork. These are angle closure eyes.

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