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 a leading cause of blindness among adults in the world. 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 optician.
This brochure is mainly about the most common kind of glaucoma, which is called open-angle glaucoma. Other kinds of glaucoma are described briefly.
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 optician 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 hospital 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?
Glaucoma screening is a normal part of an eye test.
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 getthe 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 in the first section of this pamphlet, 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.