What is glaucoma?
If you are near or past the age of 35, you have a direct interest in
knowing how to prevent blindness from glaucoma.
Glaucoma is problem worldwide and a leading cause of blindness
among adults. It is estimated that one out of
every seven blind persons is a victim of glaucoma. Practically all of
them had normal sight most of their lives. But sometime during their
40s, 50s or 60s, they went blind, for glaucoma rarely strikes until
after the age of 35. Their sight can never be restored.
There are two principal types of glaucoma, acute and chronic.
The acute type strikes suddenly, inflicting cloudy vision, sometimes
with severe pain in and around the eyes.
The chronic type--which is more common--progresses slowly and
painlessly. The victim is only vaguely disturbed by the symptoms
which come and go; as a result, he postpones visiting an eye doctor.
What is open-angle glaucoma?
In open-angle glaucoma, gradual changes within the eye lead to an
internal fluid pressure that is high enough to damage delicate
structures essential to vision. These changes occur in several stages:
- Fluid pressure inside the eye (intraocular pressure) begins to
rise. This happens because the fluid that normally fills the inside of
the eyeball flows in at the usual rate but drains too slowly. This
fluid, called aqueous humor, is a clear liquid made continuously by
cells inside the eye. Aqueous helps maintain the shape of the eyeball
and bathes and nourishes the lens and cornea, transparent tissues
located near the front of the eye. Aqueous leaves the
eye through a spongy meshwork of tissue located at the "angle" where the
cornea and iris meet.
When aqueous cannot exit fast enough, intraocular pressure rises. Why
this happens is not known for certain, although scientists think the
problem relates to changes in the drainage meshwork that are triggered
by aging and by other factors that are still not understood. Although
someone who has high intraocular pressure usually cannot feel it, an eye
care specialist can detect and measure it with an instrument called a
tonometer.
- Higher than normal intraocular pressure begins to destroy the tiny,
delicate nerve fibers that make up the optic nerve at the back of the
eye. Because the optic nerve relays visual messages from the eye to the
brain-where seeing actually takes place-the health of this nerve is
essential to sight.
Under prolonged high pressure, the optic nerve deteriorates and the
patient's field of vision gradually gets narrower (Figure 1 and 2). Surprisingly, most
people don't notice these changes until there is extensive loss of side
vision.
- If optic nerve damage is not halted, glaucoma leads to tunnel vision
and blindness.
This can happen in just a few years. Glaucoma-induced vision loss is
permanent and cannot be restored by treatment.
Therefore, to be fully effective, treatment must begin before there is serious damage to the optic nerve. That is why early detection is critical, for an eye specialist can detect what the glaucoma patient cannot: abnormalities of the optic nerve and subtle changes in the visual field. It is these key diagnostic signs, rather than elevated pressure, that indicate the presence of glaucoma. Although glaucoma is non contagious, if one eye is affected, the other eye will almost certainly develop the condition.
How is open-angle glaucoma controlled?
The goal of treating open-angle glaucoma is to preserve vision by
lowering intraocular pressure and preventing optic nerve damage. Here
are some facts about the main forms of treatment in use today:
- Drugs for open-angle glaucoma are the most widely used method of
treating this disease. These medications are taken as eyedrops or pills.
Some improve fluid drainage, while others lower pressure by inhibiting
fluid formation. Most cases of glaucoma can be controlled with one or
more medications, and a majority of patients tolerate these drugs well.
However, in a few patients intraocular pressure is not adequately
controlled by-medications. Also, some people find that the drugs' side
effects-such as stinging in the eye, blurred vision, or headaches-do not
go away after the first few weeks of use but continue to be a problem.
The patient may have trouble adhering to the prescribed dosage schedule
and may be tempted to stop taking the medication or cut back on the
dosage. In this situation, the patient should contact his or her eye
doctor to discuss the problem and the best means of dealing with it.
Changing the treatment plan without proper medical advice may allow
intraocular pressure to rise again, and the patient may suffer needless
visual loss as a result.
So, in spite of the fact that glaucoma can be controlled by
medications in a majority of patients, other forms of treatment also
play an important role in glaucoma therapy. These are described below:
- Conventional surgical techniques are intended to help fluid escape
from the eye, and thus reduce pressure. Thirty years ago, before
glaucoma drugs were available, surgery was the only effective treatment
for glaucoma.
Now ophthalmologists generally reserve surgery for patients whose
glaucoma cannot be controlled by medications and for those who are
unable to tolerate the side effects of these drugs. During the
operation, the surgeon makes an opening to create a new drainage pathway
so that aqueous can leave the eye more easily. After surgery, a few
patients still need to use medication to keep their pressure under
control and avoid loss of vision. And if the new drainage opening
closes, a second operation may be needed.
- Argon laser surgery is an innovation in glaucoma treatment. The
laser, a device that produces a high-energy beam of light, is used to
make about 100 small burns in the drainage meshwork at the edge of the
iris. Scientists think that the scars from these burns help stretch open
the holes in the meshwork, making it easier for fluid to filter out.
Laser surgery can be done in an ophthalmologist's office in a relatively
short time. Usually, people who have this surgery must continue taking
some glaucoma medication afterwards, although they may be able to lower
the dosage and still keep intraocular pressure under control. However,
the pressure-lowering effect of the laser treatment may wear off
eventually, and for this reason patients sometimes have a second or
third treatment session.
What is glaucoma screening?
Many civic groups, hospitals, and community health centers in the
United States offer glaucoma screening in an effort to identify people
who are at high risk for glaucoma but don't know it. In screening
programs, a health worker tests both eyes for increased pressure, using
a tonometer. Tonometers may worry some people because part of the
instrument touches the eye, but eyedrops can be used to numb the eye and
the procedure is quick and painless. Some programs use non-contact
tonometers which do not touch the eye, but instead measure the
resistance to a puff of air blown at the eyeball.
The person who is found to have high intraocular pressure in a
screening test is generally urged to make arrangements for a more
thorough eye examination soon. This is because screening by tonometry
can detect elevated intraoccular pressure, but cannot reveal whether
this condition has affected the optic nerve or side vision. To check for
those key signs and thus learn whether glaucoma is present, doctors must
examine the optic nerve and the field of vision. Intraocular pressure
will be checked again to determine whether it is still elevated or
whether it has dropped back to normal since the screening test. At the
end of a complete eye examination, some people will learn that they have
glaucoma and need treatment. Others will get the welcome news that they
don't have the disease.
It is important to remember, however, that "passing" a screening test
for glaucoma does not necessarily mean that you have no eye problems.
Some cases of glaucoma are missed by screening, and other eye diseases
may go undetected as well. So people who appear problem-free on the
screening test should continue to have regular, thorough eye
examinations to safeguard their visual health.
What is ocular hypertension?
Occasionally, eye examinations reveal that the pressure within one or
both eyes is above normal, but the optic nerve and visual field are all
right. This condition is called ocular hypertension. A person who has it
is at risk of developing glaucoma; the higher the pressure, the greater
the risk. If ocular hypertension is diagnosed, the eye care specialist
will be able to advise whether it is better to begin treatment to lower
the intraocular pressure right away, or whether it is preferable to
wait, have regular eye check-ups, and consider treatment only if
definite signs of open-angle glaucoma appear.
What are the other forms of glaucoma?
- In low-tension glaucoma, optic nerve damage and restricted side
vision occur unexpectedly in a person with normal intraocular pressure.
The treatments used for this condition are the ones described in the
section headed "How is open-angle glaucoma controlled?"
- In some people, an anatomical peculiarity of the eye, often
inherited, makes the angle between the iris and cornea unusually narrow
and easily closed off. This narrow angle can retard fluid drainage,
causing numerous episodes of high pressure-a condition called chronic
narrow-angle glaucoma. If the narrow angle closes suddenly and
completely, fluid backs up fast and eye pressure goes up rapidly. This
event, called acute narrow-angle glaucoma or angle-closure glaucoma, is
a medical emergency. It causes severe pain and nausea as well as redness
of the eye and blurred vision. Unless the patient has treatment to
improve the flow of fluid, the eye can become blind in as little as one
or two days. Generally, surgery is needed to restore outflow of aqueous
and prevent further angle-closure attacks. Lasers have been very helpful
as an alternative to conventional surgery for treating narrow-angle
glaucoma.
- Some infants are born with defects in the angle of the eye that slow
the normal drainage of aqueous. This relatively rare congenital glacoma
is easily recognized in affected infants, who have cloudy eyes, are
sensitive to light, and tear excessively. Surgery is usually indicated
and can prevent loss of vision if it is done soon enough.
- Glaucoma can also develop as a complication of other medical
conditions. These secondary glaucomas are sometimes associated with eye
surgery or with advanced cataracts, eye injuries, some kinds of eye
tumors, or uveitis (eye inflammations). A severe form of glaucoma,
called neovascular glaucoma, is linked to diabetes. Also, corticosteroid
drugs-used to treat eye inflammations and a variety of other
diseases-can trigger glaucoma in a few people.
How can people learn more about glaucoma?
If you are in one of the groups at special risk for glaucoma, as
described above, you should ask your doctor about this disease. He or
she can test your eyes for high intraocular pressure or refer you to an
eye specialist for glaucoma tests. If you are older than age 40,
you should have your eyes checked for glaucoma every two to three years.