| GLAUCOMA
What
is Glaucoma?
Glaucoma is a disease resulting in damage
to the optic nerve and loss of peripheral vision. It can result
from a variety of conditions, the most common being elevated intraocular
pressure (IOP), or pressure within the eye.
This pressure can damage the optic nerve
causing partial vision loss and can eventually lead to blindness
if left untreated. The optic nerve carries the images that we
see to the brain. If the optic nerve deteriorates, blind spots
and vision changes develop. Peripheral vision (side vision) is
affected first, followed by front or central vision.
Unfortunately, most people do not notice any signs of the
disease until their vision is already affected. Once they begin
to notice a problem, some vision has already been lost and can
not be regained. If the entire optic nerve is destroyed,
blindness can occur.
While elevated IOP is the most important
and most common risk factor for the development or progression
of glaucomatous damage, age, family history, black race,
diabetes and nearsightedness are others.
There are other risk factors which can
lead to glaucomatous damage in the face of normal IOP. Low blood
pressure, vasospasm from migraine headaches and/or Raynauds,
sleep apnea, and autoimmune disorders are other significant risk
factors for "normal pressure" glaucoma.
Early detection and treatment by your
opthalmologist (eye doctor) is extremely important in order to
prevent optic nerve damage and blindness from glaucoma. Loss of
vision is often preventable with early treatment.
Who
is at risk for Glaucoma?
Glaucoma is produced by many different
disorders and can occur at all ages and in all races. However,
some people are at greater risk than others.
Age: People over the age of 40.
While glaucoma can develop in younger patients, it occurs more
frequently as you age.
Family History: If you have a
parent with glaucoma, you have two to three times the risk. If
a brother or sister has glaucoma, you have five to six times
the risk of developing glaucoma.
Race: There is no glaucoma
exclusive to any race or ethnic group. However, people who are
of African decent have glaucoma four to five times more often
than any other race, and at an earlier age.
Diabetes and other medical conditions:
If you have diabetes, your risk of developing glaucoma is
three times greater than those who do not have diabetes. It is
possible that having an extreme case of myopia
(nearsightedness), a history of high blood pressure
(hypertension), or heart disease may also increase your risk.
Are
there different types of Glaucoma?
There are several types of glaucoma. The two
main categories are Primary open-angle glaucoma and narrow-angle
glaucoma.
The
Open-Angle Glaucomas
- Primary Open-Angle Glaucoma
(POAG)
This is the most common glaucoma affecting
Caucasians and persons of African ancestry. Its incidence
increases with age. POAG has no symptoms – Intraocular
Pressure (IOP) slowly rises within the eye and the disease often
goes undetected - for which reason it has been termed the
"sneak thief of sight". It is painless and the patient
often does not realize that he or she is slowly losing vision
until the later stages of the disease. However, by the time
vision is impaired, the damage is irreversible.
The pressure in the eye increases slowly
and painlessly when normal eye fluid, known as aqueous humor, is
not able to drain properly and gets backed up.
Normally, a small amount of fluid is
produced constantly, and an equal amount flows out of the eye
through a microscopic drainage system. (This fluid is not part
of the tears on the outer surface of the eye.) You can think of
the flow of aqueous fluid as a sink with the faucet turned on
all the time. In a normal eye, the faucet is always on and the
drain is always open, allowing water to easily flow through it.
In a sink, if the drainpipe gets clogged,
water builds up in the sink and the sink will eventually
overflow. If the drainage area of the eye- called the drainage
angle- is clogged, the fluid can not leave the eye as fast as it
is being produced, causing the fluid to back up. The backed up
fluid causes increased pressure to build within the eye. Over
time, too much pressure may cut-off important nutrients needed
by the cells in the optic nerve, causing parts of the optic
nerve to die, eventually leading to severe visual impairment
that is not reversible. This often goes undetected for years
because the pressure builds so gradually, occurring without any
early warning signs. This type of glaucoma tends to affect both
eyes, although you may have symptoms in just one eye at first.
Once a sufficient number of nerve cells
are destroyed, "blind spots," or scotomas, begin to
form in the field of vision. These scotomas usually develop
first in the peripheral field. Later, the central vision, which
we experience as "seeing," is affected. Once visual
loss occurs, it is irreversible, because once the nerve cells
die, nothing can restore their function.
POAG is a chronic disease, which is
presently incurable. However, it can be slowed or even
controlled by treatment.
- Pigment Dispersion Syndrome/Pigmentary
Glaucoma
Pigment dispersion syndrome is inherited
as an autosomal dominant. It is expressed more commonly in
myopes (nearsighted persons). It most often begins in the
twenties and thirties, which makes it particularly dangerous to
a lifetime of normal vision. Pigmentary glaucoma is the most
common glaucoma in persons under the age of 40, and it is far
more common than previously suspected.
The anatomy of the eye plays a key role in
the development of pigmentary glaucoma. Myopic eyes tend to have
a concave-shaped iris, which creates an unusually wide angle. In
pigment dispersion syndrome, the pigment layer of the iris rubs
against the zonules, which are like wires holding the lens in
place. This rubbing action causes disruption of the posterior
pigmented epithelial cells of the iris, releasing pigment
particles into the aqueous humor. The pigment is deposited
throughout the anterior segment, including the trabecular
meshwork, which becomes densely clogged with pigment, visible on
examination.
Miotic therapy is the treatment of choice,
but these drugs in drop form can cause disabling visual blurring
in younger patients. Fortunately, a slow-release form,
Pilocarpine Ocuserts, is well tolerated by younger individuals.
Laser iridotomy is presently being investigated in the treatment
of this disorder.
This is the most common identifiable cause
of glaucoma worldwide. Like pigmentary glaucoma, it has been
often underdiagnosed. It is found everywhere in the world, but
is most common among people of European descent. In about 10% of
the population over age 50, a whitish material, which looks on
slit-lamp examination somewhat like tiny flakes of dandruff,
builds up on the lens of the eye. This exfoliation material is
rubbed off the lens by movement of the iris and at the same
time, pigment is rubbed off the iris. Both pigment and
exfoliation materials clog the trabecular meshwork, leading to
IOP elevation, sometimes to very high levels.
Not all people with exfoliation syndrome
develop glaucoma. However, if you have exfoliation syndrome,
your chances of developing glaucoma are about six times as high
as if you don't. It often appears in one eye long before the
other, for unknown reasons. If you have glaucoma in one eye
only, this is the most likely cause. It can be detected before
the glaucoma develops, so that you can be more carefully
observed and minimize your chances of vision loss.
Low-tension glaucoma or, as
ophthalmologists now call it, normal-tension glaucoma, has
been classically defined as open-angle glaucoma developing in
a person in whom the IOP never goes above 22 mmHg. For a long
time, this was thought to be a rare disease. It is now being
realized that the number of persons with low-tension glaucoma
has been vastly underestimated. In Japan, for instance, twice
as many people have low-tension glaucoma as high-tension
glaucoma. It is this disease (or really, group of diseases
waiting to be elucidated) in which risk factors other than IOP
account for damage.
The terms high-tension and low-tension
glaucoma are misleading. Glaucomatous damage can be thought of
as consisting of two basic forms - mechanical and
nonmechanical (vascular and other). The higher the pressure,
the greater the component of mechanical damage. The lower the
pressure at which damage occurs or progresses, the greater the
nonmechanical component. If you have a pressure of 25 mmHg and
no other risk factors, it is likely that you won't develop
damage. However, if you have a pressure of 25 mmHg AND other
risk factors, the chance of developing damage is greater the
more in number or more severe these other factors are. In the
coming decade, these factors will hopefully become much more
understood. In the meantime, there is no magic number cutting
off one disease from another. It is merely a statistician's
reference point.
Primary Open-Angle Glaucomas account
for approximately 60 to 70 percent of all glaucoma cases and
it is the most common form of glaucoma , affecting over 3
million Americans. The other main type of glaucoma affects
about 10 percent of people with glaucoma, and is called Acute
(Angle-Closure) glaucoma. Unlike the other common form-
Primary (Open Angle) Glaucoma which damages your vision over a
period of months or years, Acute (Angle-Closure) glaucoma
develops suddenly.
Narrow
Angle Glaucoma
Narrow angle glaucoma affects nearly half
a million people in the United States. In China and surrounding
countries, it is more common than open-angle glaucoma. There is
a tendency for this disease to be inherited. It is more
common in hyperopes (far-sighted people), because the anterior
chamber is smaller than average. The narrower the drainage
angle, the closer the iris is to the trabecular meshwork. As we
age, the lens routinely grows larger. The ability of aqueous
humor to pass between the iris and lens on its way to the
anterior chamber becomes decreased, causing fluid pressure to
build up behind the iris, further narrowing the angle. If the
pressure becomes sufficiently high, the iris is forced against
the trabecular meshwork, blocking drainage, similar to putting a
stopper over the drain of a sink. When this space becomes
completely blocked, an angle-closure glaucoma attack (acute
glaucoma) results.
- Acute Angle-Closure Glaucoma
Unlike open angle glaucoma, in which IOP
increases slowly, the IOP increases suddenly in acute
angle-closure. This sudden rise in pressure can occur within a
matter of hours and cause severe pain and headaches. If the
pressure rises high enough, the pain may become so intense that
it can cause nausea and vomiting. The eye becomes red, the
cornea swells and clouds, and the patient may see haloes around
lights and experience blurred vision.
If the attack goes untreated, scarring of
the trabecular meshwork may occur and result in permanent
glaucoma, which is much more difficult to control. Cataracts may
also develop. Damage to the optic nerve may occur quickly and
cause permanently impaired vision.
Many of these sudden "attacks"
occur in darkened rooms, such as movie theaters, which cause the
pupil to dilate. Acute stress is another predisposing condition.
When the pupil dilates, the contact between the lens and the
iris is maximized. This further narrows the angle and may
trigger an attack. A variety of drugs can also cause dilation of
the pupil and lead to an attack of glaucoma. These include
anti-depressants, cold medications, antihistamines, and some
medications to treat nausea.
Acute glaucoma attacks are not always
full-blown. Sometimes a patient may have a series of minor
attacks. A slight blurring of vision and haloes (rainbow-colored
rings around lights) may be experienced, but without pain or
redness. These attacks may end when the patient enters a
well-lit room or goes to sleep-two situations, which naturally
cause the pupil to constrict, thereby allowing the angle to open
spontaneously.
An acute attack is an emergency condition.
If the pressure is not relieved within a few hours, vision
can be permanently lost. An acute attack may be stopped with a
combination of drops, which constrict the pupil, and drugs that
help reduce aqueous production. When IOP has dropped to a safe
level, laser iridotomy is the treatment of choice. This
is an outpatient procedure in which a laser beam is used to make
a small opening in the iris, allowing aqueous to pass directly
from the posterior chamber to the anterior chamber. Since it is
common for the other eye also to have a narrow angle, laser
iridotomy on the unaffected eye is done as a preventative
measure.
Routine examination using a technique
called gonioscopy can predict one's chances of developing
angle-closure. A special lens, which contains a mirror, is
placed lightly on the front of the eye and the width of the
angle examined visually. Patients with narrow angles can be
warned of early symptoms, so that they can seek immediate
treatment.
- Chronic Angle-Closure Glaucoma
Not all people with angle-closure
experience an acute attack. Many develop what is called
chronic angle-closure glaucoma. In this case, the iris
gradually closes over the drain, causing no overt symptoms.
When this occurs, permanent areas of closure (synechiae) can
form between the iris and the drain, and the intraocular
pressure can slowly increase over time.
How
is Glaucoma Diagnosed?
Most types of Glaucoma gives few warning signs
until permanent damage has already occurred. That's why regular eye
exams are the key to detecting signs of glaucoma early enough for
successful treatment. It's best to have routine eye checkups every 2
to 4 years after age 40 and every 1 to 2 years after age 65.
African-Americans should have yearly exams after age 50.Don't wait
for symptoms of any kind to occur. If you have one or more risk
factors of glaucoma (as indicated above), talk to your eye doctor
about scheduling regular eye examinations.
A variety of diagnostic tools should be used
to determine the presence, absence, or predesposition to glaucoma.
- Tonometry
A simple, painless testing procedure known as tonometry can alert
you and your eye doctor to the possibility you may have glaucoma.
The tonometer measures the intraocular pressure. There are two
ways that it is currently being measured.
In applanation tonometry, the eye is
anesthetized with eye drops and, at the slit lamp, a plastic prism
is lightly placed on the cornea. A strain gauge then determines
IOP. In non-contact tonometry, which is less accurate, air
is used to measure eye pressure. It does this by measuring the
amount of force needed to indent your eye. Since this instrument
does not come in direct contact with the cornea, no anesthetic
drops are required.
Testing the visual field is the most
definitive proof of optic nerve damage. At present time, almost
all visual field testing is done using computerized automated
perimetry. The patients sits facing a computerized screen and
asked to press a button whenever a flash of light appears. If
the flash of light falls into a scotoma, and is not seen, this
registers as a blindspot on the printout. Sequential visual
fields in a glaucoma patient can be used to determine whether
the disease is stable or progressing.
The optic nerve can be seen directly by
the examiner using an instrument called the opthalmoscope. The
color and appearance of the disc can indicate whether or not the
damage from glaucoma is present and how extensive it is.
In this test, a mirrored lens is placed on
the cornea, allowing the examiner to view the angle directly.
Narrow angles and angle closure can be detected. This test
should be preformed routinely on any initial complete eye
examination and annually in farsighted patients.
The diagnosis of glaucoma is not a futile
one. When it's detected and treated early, glaucoma need not
cause blindness or even severe vision loss for most people.
How
is Glaucoma Treated?
Glaucoma can be treated with eyedrops, pills,
laser surgery, eye operations, or a combination of methods. The
whole purpose of treatment is to prevent further loss of vision.
LOSS OF VISION IN GLAUCOMA IS IRREVERSIBLE. Bringing the pressure
under control will not restore lost vision, but only prevent further
vision from being lost. Keeping the IOP under control is the key to
preventing loss of vision from glaucoma. New approaches are being
developed for the treatment of low-tension glaucoma.
In order to prevent further visual loss from
glaucoma, the IOP must be constantly controlled. This requires
taking medications chronically. If a drop is given four times a day,
it is because the effect of the drop only lasts about 6 hours. Drops
given twice a day have a "duration of action" of about 12
hours. Proper taking of drops involves closing your eyes for 3 to 5
minutes with punctal occlusion. Wait 3 to 5 minutes between drops.
These techniques will allow more of the drop to get into the eye and
less into the blood stream, resulting in more effective treatment.
All drops may cause some burning or stinging
when instilled. Often, this effect is due not to the drug but to the
preservatives in the solution. It is rarely intolerable and can be
used to advantage, since it lets the patient know that the drop got
into the eye. Notify your doctor of any significant side effects,
and under no circumstances simply stop taking the medications.
Glaucoma is usually controlled with eye
drops taken several times a day, some- times in combination
with pills. For these medications to work, you must take them
regularly and continuously. These medications decrease eye
pressure, either by slowing the production of aqueous fluid
within the eye or by improving the flow leaving the drainage
angle.
MIOTICS are drops, which help to open
the drain and increase the rate of fluid flow out of the eye.
The most common is PILOCARPINE.
BETA-BLOCKERS decrease the rate at which
fluid flows into the eye. TIMOLOL and LEVOBUNOLOL appear to
have a slightly greater pressure-lowering effect than
BETAXOLOL, but the latter is safer in patients with pulmonary
disease, such as asthma or emphysema, and may have less of an
effect on heart rate. Oral beta-blockers are commonly used for
hypertension and angina and may decrease the effects of
topical beta bocker drops.
CARBONIC ANHYDRASE INHIBITORS reduce
fluid flow into the eye. Formerly, pills were the only method
of administration, and these had significant side effects, but
Trusopt and Azopt, which come in drop form, have minimal side
effects.
ALPHA-AGONISTS reduce fluid flow into
the eye and help increase drainage. They are safer
systemically than beta blockers, since they have no effect on
breathing or heart rate.
PROSTAGLANDINS increase drainage of
fluid out of the eye.There are several new drops in this
category, which include Xalatan, Rescula, Travatan, and
Lumigan.
Common Side Effects of
Anti-Glaucoma Drugs
Glaucoma medications can have side effects. It
is important not to become disturbed when reading a list of possible
side effects of a drug. Most patients do not get any side effects,
or side effects may only be a minor bother. Serious side effects are
rare--if they weren't, we wouldn't use these drugs in the first
place. Sometimes, the only way to prove a side effect is due to the
medication is to stop using it in one eye, wait for the reaction to
go away, and try it again. This is known as retesting. If you think
you have an unusual reaction to a drug, mention it. Remember that
all drops may cause burning and stinging and that any drug may
produce a rash. If you have an allergic reaction to a drug, you
should inform your doctor.
BETA-BLOCKERS: The most common systemic side
effects include exacerbation of pulmonary disease, difficulty
breathing, slowing of the pulse, and decreased blood pressure. Other
less common side effects include dizziness, fatigue, weakness,
decreased exercise tolerance, hallucinations, insomnia, and
impotence. These medications should not be used in patients with
asthma, emphysema, heart block, congestive heart failure, or those
with severe depression.
ALPHA-AGONISTS: The most common side effects
include dry mouth, mild headache, and ocular allergy. Less common
are fatigue and sleepiness. These medications should not be used in
children under the age of four.
PROSTAGLANDINS: These medications can cause a
blue or hazel iris to become brown, increase eyelash growth, and
cause red eyes. Usually, red eyes occur within the first two weeks
of starting the drops, and go away within 3 to 4 weeks. These drops
should be used with caution in patients with a history of iritis or
herpes keratitis.
For Open-Angle Glaucomas:
Argon laser trabeculoplasty (ALT) was first used
as an intermediate step between drugs and surgery, but is now being used
earlier in the disease process. This procedure takes between five to ten
minutes, is painless, and is performed on an outpatient basis. The laser
beam is focused on the trabecular meshwork and 50 to 100 burns over
180° to 360° placed on the meshwork. Contrary to what most people
think, the laser does not burn a hole through the eye. Instead, its
energy causes some areas of the eye's drain to shrink, resulting in
adjacent areas stretching open and permitting the fluid to drain more
easily. It is also possible that the laser stimulates regrowth of
trabecular cells.
ALT is successful in POAG and exfoliation
syndrome. Its success increases with the age of the patient and the
amount of pigment on the trabecular meshwork. It is also successful in
younger patients with pigmentary glaucoma. Aside from pigmentary
glaucoma, it should not be performed in-patients under age 40.
Narrow Angle Glaucoma:
Laser iridotomy is the definitive procedure. Drops
are not used for maintenance unless IOP remains elevated. In somewhat
under 10% of patients, unusual mechanisms leading to angle-closure require
an additional type of laser treatment known as PERIPHERAL IRIDOPLASTY.
The most common operation is called a
trabeculectomy. In this procedure, the surgeon removes a small
section of the trabecular meshwork to form a "drain
hole", which is covered by a "trap door". This
allows the aqueous humor to drain more easily, reducing the
pressure in the eye. This procedure is usually done under
local anesthesia either as an outpatient. The surgical site is
under the upper eyelid, and is not ordinarily visible.
Although this is relatively safe, about
one-third of patients develop cataracts within five years of
surgery. After surgery, most patients are able to discontinue
all medications. Perhaps ten to fifteen percent of patients
require additional surgery.
Trabeculectomy has become much more
successful with greatly reduced complications in the past few
years with the increasing use of anti-scarring agents
(5-fluorouracil and mitomycin C) and postoperative
manipulations (laser suture lysis and bleb needling).
Other surgical procedures include
implantation of silicone tubes (Ahmed, Baerveldt, Molteno) and
procedures designed to reduce aqueous inflow by destroying the
ciliary body (diode laser cyclophotocoagulation).
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