FORT LEE, Va. (Question: What is usually a painless, slowly progressive disease and the leading cause of blindness in the United States, often having no noticeable symptoms until catastrophic irreversible vision damage has occurred?

The answer is glaucoma. More than 3 million Americans are estimated to have glaucoma, but less than half of them are aware they have it. While certain groups of people are at higher risk to have glaucoma, the disease cuts across all segments of society.

People in the highest risk groups are those over the age of 60, those with diabetes, very nearsighted individuals, those with a relative with glaucoma and African-Americans, who are six to eight times more likely to develop glaucoma. The average age of onset can be a decade sooner for African-Americans.

Glaucoma is actually a group of diseases that cause damage to the optic nerve. The optic nerve is the main connection between the eye's photoreceptor layer (the retina) and the part of your brain responsible for transforming retinal signals into images (the visual cortex). The optic nerve itself is composed of about a million individual nerve fibers. It is gradual damage to these individual fibers that causes vision loss.

Typically, the first part of your vision affected is side or peripheral vision. Usually, the loss of peripheral vision goes unnoticed, but as the disease progresses, the area of loss moves more centrally to the extent that the person begins to notice something is wrong. At this point, care is often sought with the belief that eyeglasses may be needed. Unfortunately, prescription glasses can't fix the problem, and the damage to the optic nerve is permanent.

So, how do we keep this from happening?

The best way to find out if you are one of the 1.5 million Americans with undiagnosed glaucoma is to get regular comprehensive eye exams. During the initial exam, the doctor will check the internal pressure of your eyes and look at the optic nerve. It was once thought that high pressure in the eye was the main cause of optic nerve damage in glaucoma. High pressure is still considered a very significant risk factor, but it is now known that even people with normal eye pressure levels can have glaucoma. Also, eye pressure levels can fluctuate widely, from normal to high, throughout the day.

Because of this, it is critical that the examining doctor look carefully at the surface of the optic nerve. At the center of the optic nerve, there is often a depression called the "cup." The damage caused by glaucoma to the individual nerve fibers can cause the cup to enlarge over time. If your doctor feels that either of these findings are suspicious, additional testing will be done.

Further testing includes rechecking the eye pressure at different times of the day, measuring the thickness of your cornea, taking pictures of the optic nerve, nerve fiber layer thickness analysis and testing your peripheral vision with a special machine called a perimeter. The perimeter can detect very early changes to your side vision and is still considered the most definitive test for reaching a glaucoma diagnosis. All of these tests are noninvasive and cause no discomfort.

If you are diagnosed with glaucoma, the good news is that the treatment options carry little risk and are easy to follow. Initial treatment is usually in the form of eye drops used once or more a day. In some cases, surgery is required and in all but the most recalcitrant cases involves noninvasive laser treatments. Because glaucoma is a chronic condition that can be successfully treated, but not cured, it must be treated and monitored for a lifetime. In most cases, the progression of disease can be halted or at least greatly slowed.

The key to saving yourself from vision loss is early detection and treatment. If it has been a while since your last comprehensive eye exam (vision screenings and PHAs don't count) and even if you feel you're vision is fine, protect your vision and make an appointment to visit the Eagle Clinic at Kenner Army Health Clinic. Our clinic has the latest state-of-the-art diagnostic equipment available, and all testing can be done in our office. We currently have excellent appointment availability for all active duty, family members and eligible retirees.

Dr. David A. Mohrman has been on the staff of the KAHC-Eagle Clinic since August 2000. He attended New York University and the Illinois College of Optometry.