Glaucoma
Overview
Glaucoma is a
disease caused by increased intraocular
pressure (IOP) resulting either from a malformation or
malfunction of the
eye’s drainage structures. Left untreated, an elevated IOP
causes irreversible damage the
optic nerve
and retinal fibers resulting in a progressive, permanent loss of
vision. However, early detection and treatment can slow, or
even halt the progression of the disease.
What causes
glaucoma?
The eye constantly
produces aqueous,
the clear fluid that fills the anterior chamber (the space between
the cornea
and iris).
The aqueous filters out of the anterior chamber through a complex
drainage system. The delicate balance between the production
and drainage of aqueous determines the eye’s intraocular pressure
(IOP). Most people’s IOPs fall between 8 and 21. However, some
eyes can tolerate higher pressures than others. That’s why it may be
normal for one person to have a higher pressure than another.
Common types of
glaucoma
Open Angle
Open angle (also
called chronic open angle or primary open angle) is the most common
type of glaucoma. With this type, even though the anterior
structures of the eye appear normal, aqueous fluid builds within the
anterior chamber, causing the IOP to become elevated. Left
untreated, this may result in permanent damage of the
optic nerve
and retina.
Eye drops are generally prescribed to lower the eye pressure.
In some cases, surgery is performed if the IOP cannot be adequately
controlled with medical therapy.
Acute Angle
Closure
Only about 10% of the
population with glaucoma has this type. Acute angle closure
occurs because of an abnormality of the structures in the front of
the eye. In most of these cases, the space between the iris
and cornea is more narrow than normal, leaving a smaller channel for
the aqueous to pass through. If the flow of aqueous becomes
completely blocked, the IOP rises sharply, causing a sudden
angle
closure attack.
While patients with
open angle glaucoma don’t typically have symptoms, those with angle
closure glaucoma may experience severe eye pain accompanied by
nausea, blurred vision, rainbows around lights, and a red eye. This
problem is an emergency and should be treated by an ophthalmologist
immediately. If left untreated, severe and permanent loss of vision
will occur in a matter of days.
Secondary
Glaucoma
This type occurs as a
result of another disease or problem within the eye such as:
inflammation, trauma, previous surgery, diabetes, tumor, and certain
medications. For this type, both the glaucoma and the
underlying problem must be treated.
Congenital
This is a rare type of
glaucoma that is generally seen in infants. In most cases, surgery
is required.
Signs and Symptoms
Glaucoma is an
insidious disease because it rarely causes symptoms.
Detection and prevention are only possible with routine eye
examinations. However, certain types, such as angle closure
and congenital, do cause symptoms.
Angle Closure
(emergency)
Congenital
Detection and Diagnosis
Because glaucoma does
not cause symptoms in most cases, those who are 40 or older should
have an annual examination including a measurement of the
intraocular pressure. Those who are glaucoma suspects may need
additional testing.
The glaucoma
evaluation has several components. In addition to measuring the
intraocular pressure, the doctor will also evaluate the health of
the optic nerve (ophthalmoscopy),
test the peripheral vision (visual
field test), and examine the structures in the front of the eye
with a special lens (gonioscopy)
before making a diagnosis.
The above photos show
progressive optic nerve damage (indicated by the cup to disc ratio)
caused by glaucoma. Notice the pale appearance of the nerve
with the 0.9 cup as compared to the nerve with the 0.3 cup.
The doctor
evaluates the optic nerve and grades its health by noting the cup to
disc ratio. This is simply a comparison of the cup (the
depressed area in the center of the nerve) to the entire diameter of
the optic nerve. As glaucoma progresses, the area of cupping,
or depression, increases. Therefore, a patient with a higher
ratio has more damage.
The
progression of glaucoma is monitored with a visual field test.
This test maps the peripheral vision, allowing the doctor to
determine the extent of vision loss from glaucoma and a measure of
the effectiveness of the treatment.
The visual field test is periodically repeated to verify that
the intraocular pressure is being adequately controlled.
The structures
in the front of the eye are normally difficult to see without the
help of a special gonioscopy lens. This special mirrored
contact lens allows the doctor to examine the anterior chamber and
the eye’s drainage system.
At St. Luke’s,
another test called the Arden Screening
Test is used to confirm the diagnosis of glaucoma.
This color test may show vision changes that occur before
problems appear on the visual field test.
Treatment
Most patients
with glaucoma require only medication to control the eye pressure.
Sometimes, several medications that complement each other are
necessary to reduce the pressure adequately.
Surgery is
indicated when medical treatment fails to lower the pressure
satisfactorily. There
are several types of procedures, some involve laser and can be done
in the office, others must be performed in the operating room.
The objective of any glaucoma operation is to allow fluid to
drain from the eye more efficiently.
Should you be treated for glaucoma?
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St. Luke's Cataract & Laser
Institute provides this on-line information for educational and
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Luke's website is not intended to replace, supplant, or augment a
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viewer/user's own medical care. St. Luke's disclaims any and
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