Health & Medicine

Glaucoma

Glaucoma, family of eye diseases characterized by increased pressure within the eye and resulting loss of vision. Although the vision loss caused by glaucoma is irreversible, medication or surgery can usually control the pressure within the eye and slow or halt the progression of the disease. If glaucoma is diagnosed in its early stages, it can be treated effectively, and vision can usually be preserved.

Glaucoma occurs in two main varieties, known as chronic simple and acute glaucoma. In chronic simple glaucoma, pressure within the eye rises gradually, and vision loss progresses over a period of years. In acute glaucoma, the pressure inside the eye rises suddenly and immediate medical treatment is necessary to preserve vision. Acute glaucoma is also known as narrow-angle or angle-closure glaucoma, because the angle between the cornea (the transparent layer of tissue at the front of the eye) and the iris (the colored part of the eye) becomes smaller than normal. Chronic simple glaucoma is also known as open-angle glaucoma because the angle between the cornea and iris remains normal. This article focuses on chronic simple glaucoma, which accounts for 95 percent of all cases of glaucoma.

SYMPTOMS AND DIAGNOSIS

In its early stages, glaucoma is symptomless. The gradual increase of pressure inside the eye does not cause any pain or discomfort. As the disease progresses, however, vision begins to deteriorate. The deterioration usually begins with the peripheral vision—sight at the outer edges of the visual field. If glaucoma is left untreated, the field of vision continues to shrink until a person becomes blind.

Glaucoma can be detected before vision loss occurs by a tonometry test, which is a simple, painless part of a routine eye exam. An instrument called a tonometer blows a puff of air into the eye to measure the pressure inside the eye. Some tonometers measure pressure by means of a small plastic prism that is pressed lightly against the surface of the eye. Tests to measure peripheral vision help detect vision loss due to glaucoma. Finally, an instrument called an ophthalmoscope permits examination of the inside of the eye to detect damage to the optic nerve (see Ophthalmology).

TREATMENT

Most cases of glaucoma can be controlled with medication in the form of eyedrops or pills. These medications reduce the pressure inside the eye either by decreasing the amount of aqueous humor produced or by increasing the rate at which the fluid drains from the eye.

When the pressure inside the eye cannot be controlled by medication, surgery may be necessary. In laser surgery, a high-energy laser beam is aimed at the eye to help stretch the trabecular meshwork and make it easier for fluid to flow out of the eye. Sometimes patients who already have had laser surgery develop increased pressure inside the eye again. At that point, conventional surgery is often performed to create a new channel through which fluid can leave the eye. A valve may be surgically implanted in the eye to help control the pressure.