Topic Overview

All forms of glaucoma cause the same characteristic changes in the optic nerve, at the back of the eye, and the nerve fibers. Glaucoma causes changes in the appearance of the optic disc (notching or thinning of the edge) and changes in the nerve fiber layer (fiber defects). Tiny amounts of bleeding (hemorrhages) near the optic disc may represent ongoing damage from the disease.

Other findings are used to determine how bad the disease is. Doctors classify the severity of glaucoma in the following way:

• Ocular hypertension is consistently elevated pressure inside the eye (greater than 21 millimeters of mercury, or mm Hg) but without any evidence of damage to the optic nerve or loss of visual field. Some people who have ocular hypertension may still need treatment if the pressure in the eye is high enough to pose a risk of damaging the optic nerve over the long term.
• Corneal thickness refers to the thickness of the clear front surface of the eye (cornea). Cornea thickness, along with pressure inside the eye, helps determine your risk for glaucoma.
• Mild glaucoma refers to optic nerve damage with a normal visual field or minimal loss of side, or peripheral, vision. If signs of optic nerve damage are present without visual field loss, the person may be considered as possibly having glaucoma (a glaucoma suspect).
• Moderate glaucoma refers to optic nerve damage with moderate loss of vision in at least one eye. But sight in the center of the eye (central vision) is not affected.
• Severe glaucoma refers to optic nerve damage with loss of vision in both eyes or loss of sight in one eye that includes central vision loss.

The two basic types of glaucoma differ in relation to the cause of the optic nerve damage. A simple test (gonioscopy) can help your doctor know what type of glaucoma may be present. Treatment is based on the type of glaucoma.

• In closed-angle glaucoma, the iris (the colored part of the eye) and the lens block the movement of fluid between the chambers of the eye. The blockage causes pressure to build up and makes the iris press on the drainage system (trabecular meshwork) of the eye. The increased pressure damages the optic nerve.
• In open-angle glaucoma, the iris and lens do not block the movement of fluid between the chambers of the eye. The cause of the optic nerve damage in open-angle glaucoma is not well understood. It may be that the fluid does not drain out of the eye normally. It may be that as a person ages, his or her eyes have more exposure to risk factors or are more likely to be injured. People may also inherit the tendency to develop glaucoma.