Volume 4, Number 1
Spring, 1995
Diagnosis of Glaucoma
by George L. Spaeth, MD
Both patients and doctors tend to underestimate the value of
diagnosis. Foremost in their minds is getting and providing effective
treatment. In fact, however, the key to effective treatment of
glaucoma or any disease lies in an accurate diagnosis.
"Diagnosis" sounds simple
and, indeed, the meaning of the word is simple. Diagnosis means
putting a descriptive label on a problem so that appropriate measures
can be taken to solve it.
Unfortunately, putting the
label "glaucoma" on a set of signs (things a doctor looks for)
and symptoms (things a patient notices) is difficult because our
understanding of what causes glaucoma is still relatively meager.
The current definition of the disease is the presence of ocular
tissue damage apparently related at least partially to the pressure
of the fluid in the eye (intraocular pressure).
When the definition of glaucoma
was "a condition in which the intraocular pressure is above 21
mm Hg (millimeters of mercury, units in which pressure is measured),"
the diagnosis of glaucoma was easy. One simply measured the pressure
and that determined whether or not glaucoma was present. But that
method of defining glaucoma was wrong. It was seriously wrong!
Ninety percent of the
people diagnosed with glaucoma by that method didn't have ocular
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.
In order to get an idea of
the likelihood of whether a particular sign, for example, "intraocular
pressure above 21 mm Hg" or symptom, for example, "decreased ability
to see objects that are not straight ahead" truly supports a diagnosis
of glaucoma, that is, the presence of ocular tissue damage
apparently related at least partially to intraocular pressure,
two things about the test must be determined. First, how sensitive
is it? That is, how likely is it that the test will "find" among
those tested every person who actually has glaucoma. Second,
how specific is the test? That is, how likely is it that
everyone whom the test suggests has glaucoma, actually has glaucoma?
Since using the sign "intraocular
pressure over 21 mm Hg" to determine the presence of glaucoma
misses one third of those who actually have glaucoma, the
test is not very sensitive. Its specificity is even poorer, since
over 90% of people with this level of pressure do not have
glaucoma.
If the level of intraocular
pressure is neither a very sensitive nor specific sign of glaucoma,
how can an accurate diagnosis be made? The short, but important,
answer is: "With difficulty." There is no pregnancy test for glaucoma.
There is no dipstick indicator. There is no one test that is either
encouragingly sensitive or specific. There is no easy answer.
With this point in mind let
us consider (1) the three major types of signs the glaucoma specialist
considers in making a diagnosis: intraocular pressure, visual
field, and the condition of the optic nerve; and (2) the variety
of possible symptoms, such as decreased ability to see objects
that are not straight ahead, decreased ability to perceive motion
and to recognize color, etc.
Intraocular Pressure
As just pointed out, intraocular
pressure alone is virtually useless as a sign indicating a certain
individual has glaucoma. Still, it is one essential factor, since
glaucoma is a condition at least partially related to intraocular
pressure.
Visual Field
Another such critical but
not definitive factor is the patient's visual field. Reduced visual
field is a less sensitive but more specific indicator of glaucoma
than intraocular pressure above 21 mm Hg. However, if doctors
relied only on reduced visual field to detect glaucoma, they would
miss almost everybody who has early glaucoma. But when there is
a visual field defect, that defect is a sign that almost always
indicates that something is wrong, though that something is not
necessarily glaucoma. The problem could be due to a retinal detachment,
multiple sclerosis, an optic nerve that was made strangely at
birth, or a variety of other conditions. Nevertheless, a reduced
visual field is more likely to be a sign of glaucoma than an intraocular
pressure above 21 mm Hg. Figure 1 shows a plot of a visual field
that indicates a fairly typical defect due to glaucoma.
Figure 1
Plot of a visual field that indicates a fairly typical defect
due to glaucoma.
Optic Nerve Damage
The tissues that can be damaged
in glaucoma include the cornea, the iris, the lens, the retina,
and, most importantly, the optic nerve. Abnormality of the optic
nerve takes many forms in patients with glaucoma. One of the most
important of these is a bowl-shaped depression of the optic nerve
called "cupping," which can be detected by looking into the eye.
Cupping of the optic nerve
is one of the very important signs of the presence of glaucoma.
Simply because a person has a cup-shaped optic nerve does not
necessarily mean that he has glaucoma. However, generally, the
larger the cup, the greater the likelihood of glaucoma. Figure
2 shows an optic nerve without any signs of glaucoma. Figure 3A
shows the optic nerve of a patient with a high intraocular pressure
but an optic nerve that still looks healthy; Figure 3B shows the
same nerve after it has been damaged by pressure and the nerve
has become "cupped." Figure 4 shows a nerve that is both cupped
and has a hemorrhage.
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Figure 2
An optic nerve (the central circular area) with no signs
of "cupping," as demonstrated by the relatively small area
of white within the larger circle. |
 |
Figure 3A
Despite high intraocular pressure, the optic nerve of
this eye still looks healthy. |
 |
Figure 3B
The same optic nerve, after it has been damaged by high
intraocular pressure, now shows signs of "cupping," as demonstrated
by the larger white area in the center. |
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Figure 4
An eye with significant "cupping" as well as hemorrhage,
as demonstrated by the small dark area off the upper right
side of the central white portion. |
Symptoms
Signs, such as elevated intraocular
pressure, reduced visual field, and optic nerve cupping, are flags
that alert the physician that something may be wrong. Symptoms
are flags for the patient and the physician alike. They are, in
many ways, more important than signs because they show that whatever
is happening is affecting the patient's health. And preserving
or enhancing the patient's health is the primary task of the physician.
Thus, symptoms are especially important. Even though they may
not always be sensitive indicators of glaucoma, especially early
glaucoma, they are often highly specific, and always need to be
carefully considered.
Headaches that occur while
reading or when going into dark places, especially when associated
with misty vision or haloes, are strongly suggestive of one type
of glaucoma. Blurred vision and eye aches after vigorous exercise
suggest another type. Poor color perception and trouble seeing
at night indicate the possibility of yet another variety. Awareness
that parts of visual objects vision are missing, for example,
the first letters of words, is an indicator that something is
wrong -- perhaps macular degeneration, perhaps glaucoma, perhaps
something else. In any case, all of these symptoms require explanations.
One of the most important
symptoms of glaucoma is a general feeling that vision has deteriorated.
This general sense may merely indicate that the person needs new
glasses or that he/she has a cataract; however, it can also be
a sign of something more serious, such as glaucoma.
The Importance of Change
Perhaps the most important
thing to look for in diagnosing glaucoma is the occurrence of
change. If the intraocular pressure has risen from where it used
to be, that's reason for concern. If the visual field is less
than it used to be, something is usually wrong. If the cup of
the optic nerve has become larger, that is almost certainly a
sign that the person has glaucoma. Finally, if a patient knows
he cannot see as well as he used to, glaucoma could be the reason.
The likelihood that glaucoma
is present increases in relationship to the prominence of these
various signs and symptoms of the various types of glaucoma. Such
signs and symptoms alert the patient and the physician to the
possibility that glaucoma may be present; they indicate probabilities.
Knowing that the probability
of glaucoma is high is obviously a crucial step toward appropriate
treatment. Yet, a diagnosis simply of "glaucoma," which says nothing
about the cause or the likely clinical course of the disease in
a particular individual, is of almost no help in deciding on appropriate
treatment.
Foundation Welcomes New Researcher
Glaucoma staff physician
Jay Katz (right) and Foundation Executive Director Ken Parker
(middle) chat with the Foundation's most recent Research Fellow,
Dr. Augusto Azuara. Before coming to Wills, Dr. Azuara worked
on numerous glaucoma research projects in this country and in
his native Spain.
(Photograph by Jamie Nicholl)
Foundation Research Highlighted at National
Conference
The work of Foundation-supported investigators will again be
a strong presence at the nation's most prestigious conference
on eye research, the Association for Research in Vision and Ophthalmology
(ARVO) taking place in mid-May in Sarasota, Fla. The twelve presentations,
among the largest number accepted from any one institution, cover
a wide range of topics of crucial importance in improving the
diagnosis and treatment of glaucoma.
On the diagnosis front, there
are projects continuing the Foundation's pioneering work with
computerized image analysis of the optic nerve. As Dr. Spaeth
explains in his article in this issue of the Searchlight,
change in the condition of the optic nerve is one of the most
important clues in the diagnosis of glaucoma. Our ability to detect
and monitor these changes is being greatly improved by instruments
that convert photographs of the optic nerve into computerized
images. Computerized analysis of these images can reveal differences
in the optic nerve over time that otherwise might go unnoticed.
Studies aimed at improving
the treatment of glaucoma include investigations of the effectiveness
and safety of certain laser procedures and chemical substances.
In particular, the use of mitomycin C in glaucoma surgery has
aroused widespread interest. This agent can prevent the natural
scarring over and closing of the opening that glaucoma surgeons
create to allow fluid in the eye to exit the eye more easily and
thus reduce the pressure the fluid exerts inside the eye. But
as with any powerful substance, painstaking research must be done
to discover not only how and how much of it could be used but
also what problems it might cause.
Foundation investigators
are naturally excited at sharing the results of their hard work
with others across the nation. Although individual steps may seem
small, taken all together, real progress is being made in understanding
how to prevent the tragic blindness resulting from glaucoma.
We Need Your Help
The $100,000 bequest the Foundation
noted below underscores an important way in which individuals
can provide the crucial support needed to continue the Foundation's
activities. With declining government support, we must rely heavily
on the help of individuals. If you haven't given before, please
consider joining us now. We are making important progress in meeting
the challenge of glaucoma. With your help, we can do more--much,
much more.
Jamie Nicholl: A Researcher's
Best Friend
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Certified Ophthalmic Photographer
and Retinal Angiographer (COPRA), Jamie Nicholl, with a
photograph showing blood vessels in the back of the eye
in the background. Photographs such as this one provide
crucial information for doctors treating glaucoma patients.
Fortunately, the Foundation, in Jamie, has a highly skilled
ophthalmic photographer to assist in clinical research.
The first woman to be certified as a COPRA, she has been
an educator for the Ophthalmic Photographers Society's (OPS)
educational programs for over 15 years. Her quiet, assured
manner with students has made her a favorite instructor.
Most recently she was elected as a Fellow of the OPS.
(Photograph by Terrance L. Tomer)
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