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Overview
The term "glaucoma" refers to a group of
conditions that exhibit a gradual loss of vision,
often without symptoms. In glaucoma, vision loss
is caused by damage to the optic nerve, which transmits light signals from the retina to
the brain, where they are translated into images.
Normally, the amount of aqueous humor being
produced is equal to the amount that is draining
out. Enough aqueous is present to exert enough
pressure to keep the eye properly formed. Pressure
builds up in the eye if the aqueous humor cannot
properly drain. Increased intraocular pressure (IOP)
may ultimately damage the optic nerve.
Other factors besides intraocular pressure appear
to contribute to glaucoma. Some people with normal
pressure may experience vision loss from glaucoma,
and many people with high IOP (sometimes called
ocular hypertension) do not develop glaucoma.
However, the higher the IOP, the more likely optic
nerve damage will occur.
Incidence and Prevalence
Worldwide, there are an estimated 65 million cases
of glaucoma. There are 3 million cases in the
United States, but only one-half of those have
been diagnosed. About 2% of people between the
ages of 40 and 50, and 8% of those over 70, have
elevated intraocular pressure in one or both eyes.
There are 120,000 people in the United States who
are blind as a result of glaucoma, which accounts
for 9-12% of all cases of blindness. It is the
second leading cause of permanent vision loss and
the leading cause of preventable blindness. Open
angle glaucoma accounts for 19% of blindness in
African Americans and 6% in Caucasians. Glaucoma
is 6 to 8 times more common in African Americans
than Caucasians, and they are more likely to
become blind from it.
Asians and Eskimos have a higher prevalence of
primary angle-closure glaucoma than other ethnic
and racial groups. This type also is more common
in women, the elderly, people with
myopia, and
those with a family history of the condition.
Normal-tension glaucoma is more prevalent in
people of Japanese ancestry and in those with a
history of systemic heart disease. Family history
of this disorder also increases the risk.
Types
There are many different types of glaucoma and the
two major types are primary open-angle and angle-
closure.
Primary open-angle glaucoma
Primary open-angle glaucoma accounts for 60-70% of
glaucoma cases in the United States. In open-angle
glaucoma, the aqueous humor is unable to drain out
of the eye. For unknown reasons, the trabecular
meshwork (i.e., eye’s filtration area) does not
function normally, the pressure in the eye
increases, and the optic nerve is damaged.
Most people do not experience symptoms until their
vision is compromised and extensive damage to the
optic nerve has been done. Peripheral vision is
affected before central vision.
Angle-closure glaucoma
Angle-closure glaucoma, also known as narrow-angle
glaucoma, accounts for fewer than 10% of cases.
This type results from an abnormality in eye
structure. In most cases, the iris occludes
(blocks) the trabecular meshwork, preventing
drainage of aqueous humor and raising intraocular
pressure.
If the drainage channel is completely blocked, IOP
rises suddenly, causing acute angle-closure
glaucoma. Symptoms may be severe and include
extreme eye pain, nausea, blurred vision, and
halos around lights. Acute angle-closure glaucoma
is a medical emergency that must be treated by an
ophthalmologist immediately. Permanent vision loss
can occur within days.
Pigmentary glaucoma
This is an inherited type of open angle glaucoma
that most commonly affects myopic men in their 20s
or 30s. Myopia (nearsightedness) causes the eyes
to have a concave iris, creating a wide angle.
This causes the color (pigment) layer of the eye,
the iris, to rub off onto the lens, where it can
shed into the aqueous humor and the trabecular
meshwork. The pigment can clog the pores of the
trabecular meshwork, which prevents adequate
aqueous humor drainage and increases IOP.
Normal-tension glaucoma
Normal-tension glaucoma is also known as
low-tension, or normal-pressure, glaucoma. In this
type, "normal" IOP is too high for the
individual’s optic nerve, leading to damage of the
nerve. This condition is rare and poorly
understood. It may be that an inadequate blood
supply to the optic nerve may cause the damage.
Congenital glaucoma
When glaucoma is diagnosed before a child’s third
birthday, it is considered congenital (present
since birth). In approximately one-third of
children, it is inherited through an autosomal
recessive gene. Autosomal means that boys and
girls are affected equally, and recessive
indicates that both parents have the gene. The
risk is 25% with each pregnancy that the infant
will have congenital glaucoma when both parents
are carriers (i.e., they do not have the condition
but they can pass it to their child).
Risk Factors
Open-angle glaucoma can develop in anyone and it
occurs most often in people over the age of 40.
Many factors can increase the risk:
-
African American
-
Corticosteroid use on a regular, long-term basis
-
Diabetes
-
Family history of glaucoma
-
High blood pressure
-
High intraocular pressure in one or both eyes
-
Myopia (nearsightedness)
-
Other eye disorders (e.g., uveitis, exfoliation
syndrome, tumor, lens dislocation)
-
Over the age of 45 and not having regular eye
exams
-
Previous eye injury
The risk factor for congenital glaucoma is the
presence of an autosomal recessive gene for the
condition in both parents.
Symptoms
In most cases of glaucoma, there are no obvious
symptoms and most people remain unaware of it
until serious vision loss has occurred. Two types
of glaucoma—acute angle-closure glaucoma and
congenital glaucoma—do produce symptoms. Symptoms
of acute angle-closure glaucoma include:
-
Eye pain after watching television or upon
leaving a dark theater
-
Halos or rainbows around lights
-
Headaches (primarily in the morning)
-
Intense eye pain
-
Nausea and vomiting brought on by pain
-
Redness in the eyes
-
Sudden increase in IOP
-
Swollen or clouded cornea
Symptoms of congenital glaucoma include:
-
Enlargement and/or clouding of the cornea
-
Excessive tearing in one or both eyes
-
Sensitivity to light (the infant may close one
or both eyes in bright light)
Diagnosis
Diagnosis of glaucoma requires a thorough eye exam
performed by an ophthalmologist
or an optometrist.
The four diagnostic tests for glaucoma are
tonometry,
ophthalmoscopy,
perimetry,
and
gonioscopy.
Tonometry
There are three ways to perform tonometry (measure
IOP). In the Schiotz method, the eye first
is anesthetized with drops. The patient then lies
on a table and looks at a spot on the ceiling. A
tonometer is lowered onto the surface of the eye
for a few seconds to measure intraocular pressure.
The procedure is repeated on the other eye.
The applanation method measures how much
force is required to flatten a portion of the
cornea. This procedure is done with the patient
sitting. The side of the eye is touched lightly
with a fine strip of paper stained with an orange
dye called fluorescein. This stains the front of
the eye and helps with the examination. Anesthetic
drops are placed in the eyes. A slit lamp
microscope (instrument that utilizes a
high-intensity light to examine the eyelids,
sclera, lens, conjunctiva, iris, and cornea) is
placed in front of the patient, who rests their
chin and forehead on a support to keep their head
steady. The instrument is moved forward until the
tonometer touches the eye. Looking through the
eyepiece, the doctor adjusts the tension on the
tonometer and measures eye pressure.
In the noncontact method, the eye is not
directly touched with an instrument. This test is
performed while the patient is sitting with their
chin resting on a padded support. The patient
stares straight into the examining instrument, is
asked to fixate on a target of light, and a puff
of air is blown. Pressure is calculated by
evaluating the change in light reflected off the
cornea as the air is blown into the eye.
Ophthalmoscopy
Opthalmoscopy is used to examine the interior of
the eye, including the optic nerve. Using an
ophthalmoscope (small, hand-held instrument
consisting of a battery-powered light and a series
of lenses) the doctor can see if there has been
damage to the optic nerve.
If tonometry reveals normal pressure and the optic
nerve looks healthy, testing ends. However, if
pressure is abnormal and/or the optic nerve
appears damaged, more tests are done.
Perimetry
Perimetry is the evaluation the patient’s total
visual field (i.e., area where objects can be seen
while the eye is looking straight ahead). It can
be performed in different ways. A common method is
to have the patient stare straight ahead while the
doctor moves a light through the field of vision.
The patient indicates when the light is seen. This
helps the physician evaluate peripheral vision and
determine if vision loss has occurred.
Gonioscopy
Gonioscopy is the examination of the drainage
angle (i.e., trabecular meshwork, Canal of Schlemm),
where the aqueous fluid normally exits the eye.
The eyes are anesthetized with drops and, using a
special biomicroscope, a gonioscopy lens is placed
on the cornea. This lens has mirrors that allow
the physician to inspect the drainage area and
determine if open-angle or angle-closure glaucoma
is present.
Treatment
Glaucoma may be successfully treated by
medication, surgery, or both. Treatment depends on
the type of glaucoma and its severity, and the
underlying medical conditions, age, and health of
the patient. Patients must work with their doctors
to find the most effective treatment.
Medication
Lifelong, daily medical treatment for open-angle
and low-tension glaucoma is necessary. If
medication is discontinued, IOP increases.
Glaucoma medications help drain excess fluid from
the eye and/or decrease the amount of fluid
produced. Medications used to treat glaucoma can
be administered topically or orally and include
the following:
-
Alpha-adrenergic agonists (topical; reduce
amount of aqueous produced, some also increase
removal of fluids form the eye)
-
Beta blockers (topical; reduce the amount of
aqueous produced)
-
Carbonic anhydrase inhibitors (topical, oral;
reduce production of aqueous humor)
-
Epinephrine compounds (topical; increase removal
of fluid)
-
Miotics (topical; increase the removal of
aqueous humor from the eye)
-
Osmotic diuretics (oral; draw fluid away from
the eyes)
-
Prostaglandin analogs (topical; increase
secondary route for aqueous humor to drain)
Most glaucoma drugs produce side effects,
including these:
-
Blurred vision
-
Decreased sex drive (beta blockers)
-
Drowsiness
-
Headaches
-
Loss of appetite
-
Mood changes
-
Slowed heart rate (beta blockers)
-
Stinging in the eyes
Patients with light-colored eyes who take
prostaglandin analogs may experience a change in
eye color.
Most side effects are mild and lessen or disappear
after a few weeks. The physician should be
notified if they cannot be tolerated or are
severe. Lowering the dosage or changing the
medication usually eliminates or diminishes side
effects.
Laser Surgery
Laser surgery is recommended for those who have
not experienced favorable results from medication.
A laser is
used to make a small opening in the eye to drain
fluid. There are different types of laser surgery
and the choice is based on the type of glaucoma
and the health of the eye. Laser surgery is
usually done on an outpatient basis.
In narrow-angle glaucoma, a YAG laser is used to
make a small opening in the eye to drain fluid.
Laser peripheral iridotomy
is often used to treat angle-closure glaucoma. The
laser creates a small hole in the iris, allowing
the aqueous to flow more freely within the eye.
Argon laser trabeculoplasty
is used to treat primary open-angle glaucoma. The
laser makes tiny openings which open the
fenestration of the trabecular meshwork (drainage
area of the eye) improving aqueous drainage and
lowering IOP.
YAG laser cyclophotocoagulation
is used in advanced or aggressive cases of
glaucoma. It works by destroying selected areas of
the ciliary body that produce aqueous humor,
reducing fluid production.
Complications
Most patients obtain good results with laser
surgery, but the procedure carries some risks.
There may be a temporary increase in IOP and this
type of laser surgery can occasionally decrease
IOP to levels that are too low. The use of
glaucoma medication before and after surgery
reduces surgical risks.
Laser surgery lowers IOP, but the length of time
that it remains stable depends on the type of
surgery, the type of glaucoma, age, race, and
severity of disease. Some patients need additional
surgery. Medication is usually necessary to
control IOP following laser surgery, but many
patients are able to reduce the dosage.
Filtering Microsurgery
When medication and laser surgery are
unsuccessful, or if vision loss occurs very
rapidly, the doctor may perform filtering
microsurgery. This procedure is performed in a
hospital or outpatient surgical center. Local
anesthesia is often used with intravenous
sedation. The surgeon makes a tiny drainage hole
in the sclera. Fluid flows through this opening
and is reabsorbed into the bloodstream, and eye
pressure is lowered.
Alternatively, a small tube or valve may be placed
through the sclera incision to regulate IOP. When
the pressure rises to a certain level, the valve
opens and allows fluid to pass out of the eye.
When pressure returns to normal, the valve closes.
This procedure has a 70-90% success rate over 1
year.
Complications
Sometimes the surgical opening closes, causing
pressure to rise. This happens because the body
tries to heal the opening. Patients may also
experience blurred vision for about 6 weeks.
Vision usually returns to what it was prior to the
operation, although in some cases, vision is
improved. In a few cases, vision may worsen due to
very low IOP which results in the accumulation of
fluid in the macula.
Lifestyle and Nutrition
Exercise may reduce intraocular eye
pressure and is known to have a beneficial effect
on glaucoma risk factors such as high blood
pressure and diabetes. Results of a study indicate
that riding a stationary bicycle for 40 minutes,
four times a week reduces IOP by 20%. In a second
study, still in progress, brisk walking for 40
minutes, four times a week has eliminated the need
for beta blockers.
Some forms of glaucoma, such as angle-closure, do
not respond to exercise, and in some cases IOP may
increase temporarily following vigorous exercise.
So, it is important to discuss any new exercise
program with a physician before you start.
Severalvitamins and minerals are essential
for good eye health, including vitamins C, E, and
A, and the minerals zinc, copper, and selenium. A
large intake of caffeine over a short time can
temporarily raise IOP, and glaucoma patients are
advised to limit their caffeine intake.
Prognosis
Laser surgery lowers IOP, but the length of time
that it remains stable depends on the type of
surgery, the type of glaucoma, age, race, and
severity of disease. Some patients need additional
surgery. Medication is usually necessary to
control IOP following laser surgery, but many
patients are able to reduce the dosage.
Prevention
Glaucoma cannot be prevented. Early detection can
prevent vision loss and control the disease.
Regular eye examinations are recommended,
especially for people over the age of 35. After
age 40, eye exams should be done every 2 to 4
years, and after age 60, every 1 to 2 years.
Glaucoma testing is recommended every 1 to 2 years
after the age of 35 for those at high risk.
Eating vitamin-rich fruits and vegetables, taking
a vitamin supplement, protecting eyes from injury,
and getting medical treatment for systemic
illnesses promote good eye health. |
