How is glaucoma detected?

Conditions Expert Dr. Otis Brawley Chief Medical Officer,
American Cancer Society

Expert answer

Glaucoma is the leading cause of irreversible blindness in the world. Only cataracts, which are reversible surgically, are a greater cause of blindness. Diabetic retinopathy, a disease of the nerve in the eye, is the third-leading cause of blindness in the world and first in the United States.

There are four kinds of glaucoma. By far the most common type is primary open-angle glaucoma. The incidence of open-angle glaucoma increases with age. It is believed that more than 1 percent of adults over age 40 in the United States and Europe have this type of glaucoma. Many, indeed most, are not aware that they have it. Open-angle glaucoma is more common among people with a family history and people of African origin. Some studies suggest that high blood pressure (systemic hypertension), type 2 diabetes mellitus, hypothyroidism, and nearsightedness all increase risk of glaucoma.

Primary open angle glaucoma is often thought of as a disease characterized by increased pressure within the eye. It is better thought of as disease in which there is slow damage to the nerve in the back of the eye (the optic nerve) and a resulting slow loss of vision over time. In this condition there is usually, but not always, elevated pressure within the eyeball. Indeed, one in six people with this disease have what is called "normal pressure glaucoma." These patients usually are diagnosed because a doctor has looked into the eye with an ophthalmoscope and the optic nerve or "disc" seen in the back of the eye chamber has a hollowed-out appearance. This is called "optic cupping."

As primary open-angle glaucoma progresses, vision is lost, first around the edges of the visual field. Blindness progresses over years. It has been described as a tunnel slowly narrowing from the outer edge to the center of the field of sight. Initial vision loss around the periphery is not noticeable and requires specific testing to identify. A test called the Goldman Field is commonly used. Loss of vision caused by nerve damage cannot be recovered once it has occurred, but medical treatments can prevent the vision loss from worsening.

There are no easy ways to identify eyes that are at risk for glaucoma. There are rarely early symptoms pointing to glaucoma. The disease should be screened for in routine eye examinations and confirmed on a more comprehensive ophthalmic examination. Measurement of intraocular pressures remains the most available and best studied means of screening for glaucoma, although it is not perfect. Clearly, any patient with a high pressure detected in community-based screening or on spectacle or contact lens evaluation should be referred for a more comprehensive eye examination. Patients with optic cupping should also be referred for a more comprehensive ophthalmic evaluation.

Most experts recommend routine eye examination for every patient over age 40. This exam should be done by an ophthalmologist or an optometrist skilled in the assessment of the optic nerve and knowledgeable about glaucoma. Individuals between the ages 40 and 60 should get routine examinations every three to five years if they have no risk factors. More frequent examinations are recommended for those with risk factors such as borderline pressures, cupping, black race, family history and diabetes mellitus. I should add that diabetics should be seen annually to monitor for diabetic retinopathy. The American Academy of Ophthalmology even suggests periodic examination for men and women of African heritage between ages 20 to 39. Ophthalmologists often perform routine Goldman Field testing of patients in the diagnostic category called "glaucoma suspect" based upon risk factors and/or optic cupping.

This is a chronic disease and lifelong treatment should be managed by an ophthalmologist. Clinical studies show that long-term reduction of pressures within the eye does prevent progression of vision loss. Most drug therapy is topical. Indeed, a combination of several types of eye drops taken several times a day usually makes up the therapy for this disease. The aim is to lower pressure by decreasing fluid production in the eye. Ophthalmologists follow eye pressures and monitor vision loss through the Goldman Field test. Compliance with treatment is sometimes a problem as it can be difficult to give oneself eye drops several times a day. This is especially a problem for the elderly. Many of these medicines also are very expensive. Interestingly, the eyedrops used can have side effects beyond the eye. Some eye drops can slow the heart rate, cause irregular heart rates and even cause congestive heart failure. A small number of glaucoma patients do eventually get laser or surgical treatment.