Every year, millions of people world-wide go blind from glaucoma. Just what is this disease, and what can be done about it?

Glaucoma is a group of conditions in which the optic nerve cells in the back of the eye have died at least partly due to pressure inside the eye (intraocular pressure) exerted by the fluid in the eye (aqueous humor) which is too high for the nerve cells in that particular eye to tolerate. The optic nerve cells' job is to transform the light entering the eye into electrical impulses that can be understood by the brain. If enough of these cells die, then, some vision may be lost.

A healthy disc with a smallish cup and good color.

A badly damaged glaucomatous disc.

Now it might seem reasonable that the eye doctor can tell if you have glaucoma simply by measuring the pressure in your eye (intraocular pressure). And in fact, for many many years, glaucoma has been defined as a "a condition in which the intraocular pressure is above 21 mm Hg (millimeters of mercury, the units in which intraocular pressure is measured)." So, the doctor simply measured the pressure and that determined whether or not glaucoma was present. But that method of defining glaucoma was seriously wrong! Ninety percent of the people diagnosed with glaucoma by that method did not have eye damage related to intraocular pressure, and one-third of those who had pressure-related damage were excluded because their intraocular pressure was below the magic number of 21 mm Hg.

Since the level of intraocular pressure does not indicate with certainty whether or not glaucoma is present, how can an accurate diagnosis be made? The answer is: "A diagnosis of glaucoma is made by detecting the presence of ocular tissue damage related to intraocular pressure."

The critical question, then, is how does the eye doctor detect tissue damage that is pressure-related? The short, but important, answer to that question is: "With difficulty." There is no pregnancy test for glaucoma. There is no dipstick indicator. There is no easy answer.

One of the things making the doctor's job difficult is the fact that, though there are many signs and symptoms of the various types of glaucoma, almost all of them also could indicate other conditions, and not glaucoma. For example, decreased visual field, (the area visible to a person -- straight ahead, up, down, and to the sides) may be due to a retinal detachment or multiple sclerosis, or an optic nerve that was abnormally formed at birth. The optic nerve can have a bowl shape (which is called "cupping") because the person was born with a bowl-shaped nerve, has syphilis, is near-sighted, or has glaucoma damage.

Nevertheless, the size of the optic cup is definitely related to the presence or absence of glaucoma: the larger the cup of the optic nerve, the greater is the likelihood that the person has glaucoma.

In the type of glaucoma that is most common among people in the United States, the optic nerve gradually becomes damaged over a period of 10 to 30 years. The loss of nerve fibers occurs so gradually that the decrease in vision is usually not noticed until over half of the nerve fibers have died. Additionally, the area of seeing that is lost first is on the nasal side and involves one eye much more than the other. Consequently, it often isn't until both eyes have lost a great deal of vision that the afflicted person recognizes the loss. Contrary to what many people believe, the peripheral vision to the side is actually the last part of the vision to be lost in a person who has glaucoma.

A thoughtful, thorough examination which takes into account a patient's family background (since glaucoma seems to be hereditary), intraocular pressure, visual field, and the condition of the optic nerve will allow the eye doctor in most cases to accurately determine whether a person has glaucoma. Once this basic determination has been made, the doctor will devise an appropriate treatment plan. He or she will then carefully monitor the optic nerve appearance, visual field and intraocular pressure to determine if any further damage is being sustained.

Treatment usually is designed to lower intraocular pressure to a level that will no longer damage the optic nerve. Sometimes this is done with eye drops, sometimes by altering certain structures in the eye either with a laser or a knife. Although many patients prefer treatment with eye drops because they seem to be the least traumatic, they may not always be the best treatment for a particular individual. They may seem "harmless," but, depending on the individual, eye drops can have very significant side effects on the body as well as the eye. Similarly, many patients believe laser surgery is preferable to surgery with a knife, since it seems to be less "invasive." Again, however, this is not necessarily true, and surgery with a knife may be preferable.

Research is under way, including here at Wills Eye Hospital in Philadelphia, designed to increase: (1) our understanding of just why intraocular pressure becomes high enough in certain individuals to damage their optic nerve, (2) our ability to accurately diagnose glaucoma, and (3) the effectiveness of treatment. This research, together with the care taken by individuals to have regular, thorough eye examinations, will go a long to minimize the devastating effects of glaucoma.