Volume 4, Number 2
Fall, 1995
What is Angle-Closure Glaucoma?
by George L. Spaeth, MD
In the previous issue of the Searchlight I discussed the general
way in which a diagnosis of glaucoma is made on the basis of measurements
of the pressure in the eye, visual field examinations, and direct
observation and photographic evaluation of the optic nerve.
Making such a diagnosis is obviously a crucial step toward appropriate
treatment. Yet, a diagnosis simply of "glaucoma" says
nothing about the cause or the likely clinical course of the disease
in a particular individual; a diagnosis simply of "glaucoma"
is of almost no help in deciding on appropriate treatment.
Seeking the Cause
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't tell the patient what
it is that 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.
The Eye's "Angle"
In a normal eye, the fluid in the front part of the eye, the
aqueous humor, is produced and exits the eye in such a way that
it exerts 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."
When the Angle Gets Blocked
One problem that can develop is that the angle gets blocked,
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 may not be allowing sufficient outflow for a variety
of reasons. Maybe the person was born with a narrow angle, and
as he aged and it became even narrower (as it does in almost everybody),
it simply closed off by itself.
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.
Treating Angle-Closure
These three types of angle-closure are just a sampling of the
problems that can keep the eye's drainfrom 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 at the side of 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 to block the drain. The hole allows the pressure
in front of and behind the iris to balance out, so that it falls
back towards its proper position, away from the outflow ain, permitting
the aqueous humor 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 an 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 (a tube shunt) that bypasses the
blocked angle and allows the aqueous to exit at the back of the
eye.
Knowing the Cause Is Not Enough
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 oseonly 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 an hour.
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 higher for long. In these cases, the pain may be
very severe, but vision will be impaired only temporarily.
Each Case is Unique
I hope I've shown with this brief discussion of some of the varieties
of just one type of glaucoma, angle-closure glaucoma, 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 try to understand
who they are, what they need, expect, and hope for.
Figure 1
The human eye, showing the main features of the front part (anterior
chamber) of the eye and the optic nerve.
Figure 2
Normal open anterior chamber angle showing the flow of aqueous
humor through the pupil and out the Canal of Schlemm.
Figure 3
Narrow anterior chamber angle, open but capable of closing.
Figure 4
Closed anterior chamber angle with flow blocked.
Foundation Seeks Support to Bring Major Researcher
Here
Alon Harris, PhD, a renowned glaucoma researcher presently at
the University of Indiana, has agreed in principle to come to
the Glaucoma Service at Wills Eye Hospital to head up our research
program as Research Professor.
The Foundation has raised
about half of the $1.5 million needed to establish the endowed
Research Professorship that will enable Dr. Harris to come.
The Professorship will be
named for the donor(s) of the remaining funds.
Giving Stocks: A Win-Win
Proposition
Year-end is a popular time for making stock gifts.
Many thoughtful donors review their portfolio and select those stocks
that have appreciated the most and that they have had for more than
a year.
Suppose a stock had grown
from $15 a share to $75 a share over the past few years. If a
stockholder asked her broker to sell the stock, she would owe
tax on the $60 of appreciation for each share she sold.
However, if she donated the
stock to the Glaucoma Service Foundation, she would avoid this
tax on the appreciation and receive, instead, an income tax deduction
for the full value of the stock. What's more, because the Glaucoma
Service Foundation is a qualified charitable organization, it
would sell the stock and avoid any tax on the appreciation. A
win for the stockholder; a win for the Foundation's efforts to
discover improved ways of diagnosing and managing glaucoma.
Wike Charitable Trust GIves $100,000
The Trustees of the Jesse R.
Wike Charitable Trust notified the Foundation in May that they
will donate $100,000 in 1996.
Using Ultrasound Biomicroscopy
to Look at Eye's Angle
How can doctors find out what's causing problems in our bodies,
especially when, as usually is the case, the cause is hidden from
easy view? X-rays are useful for finding broken bones. Possibly
malignant tissues can be removed and examined under a microscope.
Both of these are examples of imaging. If we want to see something
invisible to the naked eye, we have to find some way to create
an image of it that we can see.
Another way of making something
invisible visible involves the use of very high-frequency sound
waves, that is, ultrasound. Ultrasound is now used routinely to
look at the fetus in a mother's womb. High-frequency sound waves
are focused on the womb and, like all sound waves, are variously
reflected depending on the surface they strike. The reflected
waves are then turned into corresponding light waves. An image
of the fetus then appears, allowing the doctor to determine, for
example, whether it is going to be a girl or a boy.
Suppose now we were trying
to see something that not only is inside the body but also very
small, such as the complex structures within the eye. Ultrasound,
again, can be used to produce an image, but this image must be
magnified in order to reveal the details. This kind of imaging
is known as ultrasound biomicroscopy--that is, using high-frequency
sound to look at tiny living tissues.
Ultrasound has been used
for over 20 years to look at the back part of the eye. This is
still done in patients with a cataract to see if there is some
problem (like a tumor or detached retina) that might keep the
patient from seeing well even if the cataract is removed.
The latest ultrasound biomicroscopy
equipment is especially useful for looking at the front part (anterior
chamber) of the eye. In particular, it provides a very good image
of the "angle" of the eye--that part of the eye, as Dr. Spaeth
explains in his article in this issue, that can become blocked,
causing damaging levels of pressure to build up.
Ultrasound biomicroscopy can
be used in glaucoma patients to see if the angle is blocked, and,
if it is, precisely what is blocking it, and how much it is blocked.
Through ongoing study of these images from many patients, our
researchers are learning more and more about angle-closure glaucoma.
Searching for Answers
Dr. James Augsburger (left)
of the Oncology Service staff of Wills Eye Hospital and Dr. Courtland
Schmidt (right) of the Glaucoma Service staff examine an image
of the front part of the inside of the eye created by ultrasound
biomicroscopy. This instrumentation allows doctors to directly
observe the angle of the eye as discussed in Dr. Spaeth's article.
Since September, Dr. Augsburger
has been sharing his profound knowledge of clinical research methods
at weekly meetings with the Glaucoma Service research team.
(Photograph by Jamie Nicholl)
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