By Dr. George L. Spaeth
The word “glaucoma” sounds so specific and so scientific it’s only natural that when an eye doctor tells a patient, “You have glaucoma,” the patient feels something very meaningful has been said. Yet, if the doctor can not tell the patient what is actually causing the glaucoma, and, thus, when and to what extent it is likely to affect his or her vision, the word “glaucoma” may only serve to frighten the patient, making appropriate treatment even more difficult.
It is important, then, that the physician further refine the diagnosis of glaucoma by determining as accurately as possible its specific cause and, based on that, its likely course. As discussed previously, the general cause of glaucoma damage is pressure inside the eye too high for the eye to tolerate, although there are clearly other factors also involved. Seeking a more specific diagnosis, the doctor must try to discover what it is that is causing this excessive pressure, whatever its level, and any other factors that may be involved.
In a normal eye, the fluid in the front part of the eye, the aqueous humor, is produced and exits the eye exerting just enough pressure to keep the eye properly formed without damaging it. That is, the amount of new aqueous that is constantly being created by the eye is balanced by the amount that is constantly draining out of the eye at a place in the eye called the “angle.”
The angle received its name as the angle where the iris meets the cornea. An angle of 15 degrees between the iris and cornea means a much smaller anterior chamber of the eye with little space between the iris and Schlemm’s Canal, the actual drain of the eye, than would be seen with a 30 degree angle. If the angle gets blocked, fluid will continue to be made at a normal rate but will be unable to exit the eye, allowing the pressure in the eye to build up to a harmful level. This is what happens in one type of glaucoma known as “angle-closure” glaucoma.
The angle of the anterior chamber of the eye, i.e., the junction of the cornea and sclera externally and the iris internally. The drain of the eye, the canal of Schlemm, is covered by a sieve of tissue called the trabecular meshwork. In this picture it is the thin circular brown line in front of the iris. The brown pigment has been sieved out of the fluid in the anterior chamber (aqueous humor) and deposited in the trabecular meshwork.
The angle may not be allowing sufficient outflow for a variety of reasons. If the person was born with a narrow angle, it will become even narrower with age. If the angle becomes too narrow, the iris may become caught in the drain, blocking it.
Or it may be not be draining properly because a blow to the eye loosened the lens, allowing it to move forward and push the angle closed.
Another possibility is that diabetes has caused abnormal blood vessels to grow over the angle, stimulating scar formation in such a way that the iris has been pulled onto the surface of the angle, again blocking the outflow of aqueous.
These three types of angle-closure are just a sampling of the problems that can keep the eye’s drain from working properly. You might suspect, and you would be right, that these very different causes of blockage call for very different types of treatment.
For example, a person born with a narrow angle that has become even narrower with age can be treated by using a laser to make a tiny hole in the iris, allowing the aqueous to drain out more easily. This procedure, known as laser iridotomy (that is, making a tiny hole in the iris with a laser), is useful in cases in which the iris has come forward to block the drain. The hole allows the pressure in front of and behind the iris to be equalized, so that it falls back towards its proper position. With the iris away from the outflow drain, the aqueous humor is again allowed to pass out of the eye normally. Laser iridotomy is extremely effective in many cases of angle-closure glaucoma, but it is important that it be done before the angle closes off. Thus, patients need examinations of the anterior chamber angle to determine if they are predisposed to this problem.
The person with an angle-closure glaucoma caused by a dislocated lens, the second example given, probably should have the dislocated lens removed, so that the angle opens back up naturally. This can be a hazardous procedure and should be done only after careful consideration. However, if it is done at the appropriate time, the pressure will return to normal, and no more damage will occur.
A totally different kind of treatment is required for an angle blocked by abnormal blood vessels, the third type of “angle-closure” mentioned above. It is extremely difficult to make a drain full of abnormal blood vessels work again. Thus, when people are predisposed to getting this type of glaucoma, it is important to take all possible preventive steps addressing the basic causes of these abnormal vessels. Such causes include blockage of the artery or vein that supplies and drains the retina, tumors in the eye, diabetic vessel changes, or inadequate blood flow to the eye (as happens when the large arteries in the neck are blocked).
If the development of abnormal new blood vessels is caught early enough, when the abnormal vessels are just beginning to form, laser treatment of the retina can often be helpful. But once the angle is closed with blood vessels, the angle drainage mechanism is usually permanently damaged, so some type of surgery is usually required to bring the pressure back to a safe level. This may involve placing a plastic drain (an aqueous shunt) that bypasses the blocked angle and allows the aqueous to exit the eye to be absorbed into the vessels outside the eye.
You can begin to see that, even though a diagnosis of “angle-closure glaucoma” is more helpful than a diagnosis simply of “glaucoma,” appropriate treatment requires a specific understanding of just what is causing the pressure in the eye to be at harmful levels.
But even knowing the specific reason for angle-closure is still not enough. The doctor also must judge when and to what extent the patient, because of deteriorating vision, will begin to have difficulty doing things he’s used to doing.
At the low end of the scale, it may be that the cause of damaging high pressure may have disappeared, so that no more damage will occur. If this is the case, the best treatment is often no treatment.
Another possibility is that the glaucoma is progressing slowly, so slowly that the eye probably will lose only a little bit of vision even over a period as long as 25 years. In such cases, although some treatment is necessary to lower the pressure, the treatment should carry with it as little risk of harmful side effects as possible.
On the other hand, in some cases, when, for example, the angle suddenly becomes completely covered by the iris, glaucoma damage may occur very rapidly, leading to total blindness within a few hours. Even here, however, each case is different. In some cases, when the pressure is very high, the tissue that produces the fluid (the ciliary body) may stop making fluid so that the pressure doesn’t stay high for long. In these cases, the pain may be very severe, but vision will be impaired only temporarily.
We hope this brief discussion of some of the varieties of just one type of glaucoma, angle-closure glaucoma, has shown why a diagnosis simply of “glaucoma” or even “angle-closure glaucoma” is in itself not really very meaningful or helpful. No matter how many diagnostic labels are applied, every condition, just like every person, is different.
In fact, one of the great shortcomings in modern medicine and even more generally of our whole society is the way we label people — “white,” “type A” “elderly,” male.” Yes, these labels can be of some help in raising questions and possibilities. For example, black people of African descent are more likely to have glaucoma damage than white people of European descent. But how helpful is this information to the doctor faced with an individual patient? Not very. After all, most black Africans never get glaucoma damage and many white Europeans do.
The challenge is to view one another as totally unique and worthwhile. Treatment will be most successful when this uniqueness is properly recognized, appreciated, and utilized. Patients can help get optimal care by insisting that their doctors really understand exactly who they are, and what they need, expect, and hope for.