Glaucoma
What
is glaucoma?
Glaucoma
is an eye disease that impairs the
victim’s vision through damage
to the optic nerve. In many cases,
this damage results from increased
intraocular pressure. The disease
is most prevalent in older people,
although some types of glaucoma can
affect young people as well.
What
are some of the different types of
glaucoma?
Different
types
of glaucoma are principally determined
by the angle where the iris and the
cornea meet in the eye. Closed-angle
glaucoma is determined by a particularly
narrow iris-cornea angle that increases
intraocular pressure. Open-angle glaucoma
encompasses the types of glaucoma
that occur when this angle is proportioned
correctly.
The
most common type of glaucoma is called
primary open-angle glaucoma. This
form of glaucoma causes intraocular
pressure by inhibiting the drainage
of fluid from the eye. The fluid,
called the aqueous humor, is produced
by glands behind the iris. It flows
around the iris and lens, providing
essential nourishment, and then is
drained out through a filter. In primary
open-angle glaucoma, this filter –
called the trabecular meshwork –
fails. It is unclear why this occurs;
however, when it does, the fluid remains
in the eye, increasing the pressure
inside. The weakest point in the structure
of the eye is the spot where the optic
nerve enters the sclera. If the intraocular
pressure increases enough, it damages
or destroys the cells of the optic
nerve. This damage causes vision
loss and can eventually lead to
permanent blindness.
Another
type of open-angle glaucoma is normal-
or low-tension glaucoma. It contributes
about one third of all open-angle
glaucoma cases. It is termed “low-tension”
because the intraocular pressure in
its victims is statistically normal.
There is much speculation on how this
type of glaucoma occurs. One of the
foremost theories is that there is
poor blood flow to the ocular nerve.
Also speculated is that the cells
of the ocular nerve are more susceptible
to pressure, meaning pressure within
the normal range has damaging effects.
Its results are similar to primary
open-angle glaucoma: the gradual loss
of vision.
A
third type of chronic open-angle glaucoma
is pigmentary glaucoma. This disease
is inherited and occurs most often
in myopic, or nearsighted, people.
The myopia causes the iris to rub
on the lens and flake pigment. The
flakes of pigment clog the trabecular
meshwork, increasing intraocular pressure
and injuring the optic nerve. Pigmentary
glaucoma is sometimes accompanied
by a disease called exfoliation syndrome.
When a person has exfoliation syndrome,
a white substance builds up on the
lens. The movement of the iris flakes
this material away at the same time
that the pigment is being rubbed off,
and the two clog the trabecular meshwork.
Pigmentary glaucoma also results in
the gradual loss of vision.
Another
major type of glaucoma is called closed-angle
or angle-closure glaucoma. It is the
second most frequent form of the disease
after primary open angle glaucoma.
Closed-angle glaucoma is often inherited,
though it may take a long time to
develop. In this disease, a small
angle between the sclera and the iris
inhibits the flow of the aqueous humor.
The angle may grow smaller as the
lens matures, causing very slow deterioration
of the patient’s vision. However,
sudden changes in the size of the
angle can also occur, such as when
the pupil dilates. If the sudden angle
closure pinches the trabecular meshwork
to the point that it is completely
blocked, the optic nerve can be severely
impacted and a glaucoma attack can
occur.
Acute
glaucoma, also known as a glaucoma
attack, occurs quickly, sometimes
in a matter of hours. Unlike chronic
glaucoma, a glaucoma attack can be
very painful. The eye usually becomes
very red, the vision blurs, and haloes
may appear surrounding lights. A glaucoma
attack typically occurs in patients
with closed-angle glaucoma, when conditions
dramatically narrow the cornea-iris
angle. This can occur when a person
enters a dark room and the pupil dilates
or when a person becomes excited.
The attack may be minor, meaning that
once the pressure drops, the attack
subsides and vision returns. For instance,
if the pupil dilated from darkness,
walking into a well-lit room can cause
it to constrict and the attack to
pass. However, glaucoma attacks can
also be very serious. In some cases,
if acute glaucoma is not treated immediately
after the onset, the trabecular meshwork
can become scarred, leading to chronic
glaucoma. Permanent blindness can
ultimately occur.
Glaucoma
can also result from eye trauma. Jarring
blows, penetrating strikes, or exposure
to chemicals can cause glaucoma, either
acute or chronic.
What
are the symptoms?
Typically
chronic glaucoma has few symptoms.
There is often no pain whatsoever.
The intraocular pressure can give
a doctor an intimation of developing
glaucoma, although even this characteristic
can be misleading. Unfortunately,
the first true indication of glaucoma
often comes when blind spots begin
to appear.
Onset
of acute glaucoma is usually accompanied
by sharp pain in one or both of the
eyes, drastic blurring of vision,
and haloes or starbursts. The eyes
can also become extremely bloodshot.
What
are the treatments for glaucoma?
Glaucoma
treatments are typically intended
to lower intraocular pressure. The
two primary means of accomplishing
this are medication and surgery.
One
way in which glaucoma medication works
is to increase the rate at which fluid
flows out of the eye. This is most
often accomplished through the use
of miotics. These medications, which
usually come in eyedrop form, constrict
the pupil and open the cornea-iris
angle. They are often a primary treatment
for a glaucoma attack, and are used
regularly to treat pigmentary glaucoma
as well.
There
are also glaucoma medications that
decrease the rate at which fluid flows
into the eye. These types of medication
can come in both eyedrop and pill
form. Typically, the eyedrop is prescribed
first because its effects are milder,
but pills may be used if the patient’s
symptoms are not relieved. One or
both types are often administered
in response to a glaucoma attack.
Surgery
can also relieve intraocular pressure.
The most common surgical approaches
to glaucoma adjust the trabecular
meshwork to increase the flow of aqueous
humor out of the eye. This may be
accomplished through laser surgery
or conventional removal of tissue.
Laser
surgery on the trabecular meshwork
is usually an intermediate step between
medication and traditional surgery.
The most common laser procedure for
glaucoma is called trabeculoplasty,
and it is used to shrink the trabecular
meshwork and allow a small amount
of free drainage around it. Typically,
the procedure is painless and recovery
is quick and complication-free. However,
the chances are slight that laser
surgery will permanently cure a patient’s
glaucoma; many trabeculoplasty patients
eventually have to undergo another
procedure.
Sooner
or later, the surgeon may have to
resort to traditional surgical methods.
The most frequently performed procedure
to decrease intraocular pressure is
trabeculectomy. In trabeculectomy,
the surgeon removes a small portion
of the trabecular meshwork. This has
been proven to effectively reduce
pressure, and it very frequently results
in the patient’s discontinuation
of medication. However, there is one
alarming possible side effect of trabeculectomy:
the development of cataracts. About
one out of every three trabeculectomy
patients develop cataracts within
5 years of surgery.
One
procedure that does not impact the
trabecular meshwork at all is called
laser iridotomy. In the procedure,
a laser is used to produce a hole
in the iris, allowing fluid to flow
around the meshwork. Iridotomy is
usually quick and painless. Even if
only one eye is affected, the procedure
is typically performed on both eyes
as a preventative measure. Currently,
laser iridotomy’s primary use
is in response to glaucoma attacks.
However, it is also being researched
as cure from some chronic forms of
glaucoma such as pigmentary glaucoma.
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