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EYE DISORDERS
GLAUCOMA
Glaucoma is a common eye disease, with an estimated
2 million Americans being affected. It is the second most common cause
of legal blindness in this country, and the first among African Americans.
To make the situation even worse, glaucoma usually offers no symptoms
until it is very advanced. Vision lost from glaucoma cannot be regained.
This section discusses adult onset glaucoma, its diagnosis, and treatment.
Topics Include:
Glaucoma is an eye disorder where the nerve containing visual information
from the eye (the optic nerve) is damaged over time. Usually, a high
pressure inside of the eye leads to a gradual loss of nerve fibers contained
within the optic nerve. This leads to a loss of vision, usually involving
the peripheral vision first. The relationship between the pressure inside
of the eye and the risk of glaucoma is complicated:
- The normal eye pressure usually ranges between 10 and 21, with an
average of 16, when measured by an eye doctor. The eye pressure (or
IOP, for intra-ocular pressure) can vary throughout the day, and is
not affected by blood pressure, reading, sinus problems, or eye-strain.
- Some people can have a high eye pressure (over 21) consistently,
and yet never suffer any optic nerve damage from the pressure.
- Most people with elevated eye pressure will eventually get damage
to the optic nerve. If the pressure approaches 30 or higher, the damage
may come faster and be more severe.
- Some people can get optic nerve damage with even what is considered
to be a NORMAL pressure (under 22). This type of glaucoma is termed
"low tension glaucoma".
If the nerve becomes damaged by glaucoma, blind
spots in the vision will occur. Usually this affects the peripheral
vision first (the side vision). If it is untreated, the central vision
can be lost from glaucoma as well. Usually both eyes are affected by
glaucoma if it is present, but one eye may be affected more severely.
Blind
Spot Examples - To view some examples of subtle and not so subtle
blind spots found with glaucoma.
There are many different types of glaucoma, but basically they fall
into two categories: open-angle and closed-angle glaucoma. The "angle"
of the eye is an area where fluid drains from the eye back into the
blood circulation. The eye produces fluid on the inside in order to
maintain its shape and for nourishing structures within the eye. This
fluid is drained by an area located at the junction of the cornea and
the iris inside of the eye.
- In "open-angle" glaucoma, this drainage area appears to
be unobstructed when viewed by the physician. This is the most common
form of glaucoma, and it is not fully understood why the pressure
within the eye becomes elevated. It is also known as "primary
open-angle glaucoma" (POAG) or as "chronic open-angle glaucoma"
(COAG).
- In "closed-angle" glaucoma, the drainage angle is physically
blocked, and is not visible to the physician.
Open-angle glaucoma
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Open-angle glaucoma is the most common form of glaucoma
by far. It rarely offers any physical symptoms: there is no pain,
no pressure sensation, no blurring of vision. The intra-ocular pressure
is often only mildly elevated, and the optic nerve is gradually
damaged over a period of months and years. Other, less common types
of open-angle glaucoma include: |
- Pigmentary glaucoma: Here, pigment granules liberated by the iris
and other structures within the eye are thought to clog the outflow
channels. This variety tends to occur in younger individuals, and
may be worsened by vigorous physical activity, which may disperse
more pigment. This type of glaucoma can give symptoms because the
pressure may spike to very high levels at times (over 40). This may
cause eye discomfort, blurred vision, rainbows or halos around lights,
or headache.
- Low tension glaucoma (or normal pressure glaucoma): This sub-category
of open-angle glaucoma is characterized by optic nerve damage occurring
at normal or even low intra-ocular pressures. This may be common in
the very elderly (over 80). Other tests need to be done to diagnose
this condition.
Closed-angle glaucoma
| Closed-angle glaucoma is more rare, but also more
severe in symptoms. During an attack of "angle-closure",
the iris rotates toward the cornea and blocks the outflow channels
suddenly and completely. Intra-ocular pressures over 60 are not
uncommon, which can cause severe eye pain, nausea, vomiting, redness,
blurred vision with rainbows around lights, and sudden loss of vision.
This requires emergency treatment to cure, and usually requires
a laser procedure to be done to break an attack or prevent future
attacks. Often, the other eye, if at risk of an attack, is treated
preventably by laser. |
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Glaucoma can affect people of all races, background, and age, and can
occur in people who are otherwise completely healthy. However, there
are certain groups of people who are especially at risk for glaucoma.
These include:
- People over 60 years old
- African-Americans
- People with a family history of glaucoma
- People with vascular diseases such as diabetes
- People who are very nearsighted
It is recommended to have a complete eye examination for glaucoma (ref.
2):
- At age 35 and 40
- Every two to three years after age 40
- Every one to two years after age 60
- Every one to two years after age 35 if there are any special risk
factors, as listed above
The diagnosis of glaucoma cannot be accomplished by a brief screening
examination. While free pressure screenings done at health fairs can
help to detect people with a high eye pressure, a normal pressure found
does not rule out that glaucoma is present. This is because the pressure
can fluctuate throughout the day, and because some people with glaucoma
never have an elevated pressure.
The examination to determine whether or not glaucoma is present includes
the following:
- A complete eye examination, including checking the vision, pupil
reaction, biomicroscopic examination of the structures of the eye,
the intraocular pressure (tonometry), and an examination of the optic
nerve and retina.
- The eye pressure can be checked in different ways. The standard
method is called "applanation tonometry". In this method,
anesthetic drops are placed in the eyes and a device using a blue
light gently touches the eye. Another method is "air-puff"
tonometry.
- Special attention needs to be paid to the appearance of the iris,
and of the drainage angle of the eye.
- The optic nerve needs to be evaluated closely for evidence of damage
from glaucoma.
If there is suspicion for glaucoma, a "visual field" test
can be done. This test is usually scheduled separately, and is run by
a technician. This test usually lasts about 20 minutes, and the peripheral,
or side, vision of each eye is tested for any blind spots. The ophthalmologist
will then review the results of the test.
The "glaucoma suspect"
A person is considered a "glaucoma suspect" if there are risk
factors present for glaucoma, but not any evidence of damage to the
peripheral vision. Some cases of "glaucoma suspect" could
include:
- A person with a high eye pressure, but normal nerve appearance and
normal visual field testing. (Also known as "ocular hypertension".)
- A person with glaucoma in the family, and a suspicious appearance
to the optic nerve, but normal visual field testing.
- An African-American with a borderline high eye pressure and a family
history of glaucoma.
Usually, cases suspicious for glaucoma are followed more closely, with
follow-up visits coming every 4 to 6 months.
The diagnosis of "glaucoma" itself
A diagnosis of glaucoma can be made if there is suitable evidence for
glaucoma based on the eye examination performed by an ophthalmologist.
Usually to diagnose glaucoma, there are blind spots in the field of
vision. Other situations where glaucoma may be diagnosed include:
- There is a very high eye pressure (over 30) or evidence of angle-closure
glaucoma.
- If there are repeatedly high eye pressures approaching 30 even in
spite of a normal visual field test. Damage may be imminent in these
cases.
- If there is progressive worsening of the appearance of the optic
nerve or worsening of blind spots on the visual field test.
Once diagnosed with glaucoma and treatment is initiated, follow-up
examinations are usually at least every 3 months.
- Open-angle glaucoma usually cannot be cured, only controlled.
- Damage done to the optic nerve, and loss of peripheral or central
(reading) vision usually cannot be restored, only prevented.
- Proper use of medication by the patient, and consistent follow-up
examinations are of the utmost importance in controlling glaucoma.
Once glaucoma is diagnosed, the main goal of treatment is to lower
the pressure within the eye to the point that damage will not continue.
Usually, initial treatment is in the form of eyedrop medications.
Some important points about glaucoma medications include:
- Eyedrops used for glaucoma are administered at different times depending
on the medication. Some are only once a day, while some are used up
to four times a day. It is important to fully understand the physician's
instructions about how often to use the medication.
- If a medication is to be used more than once a day, it is important
to spread out the dosages as much as possible. (Example: If an eyedrop
is to be used twice a day, and the first dosage is given at 7:00 AM,
use the second dosage around 7:00 PM, not midnight.)
- Once the eyedrop is administered, hold the eyes closed for a few
minutes and apply pressure to the inside corner of the eye. This helps
to prevent drainage of the eyedrop immediately into the tear drainage
system (and away from the eye).
- Since some of the eyedrop will inevitably get into the tear drainage
system, some of the medication could be absorbed into the general
circulation. Glaucoma eyedrops can cause physical symptoms in some
people. Your physician will discuss this with you.
Once the eye pressure has been lowered sufficiently with medication,
the glaucoma is usually monitored about every 3 months. Once a year,
the optic nerve is re-evaluated, and the visual field test is repeated.
If damage still seems to be occurring, the eye pressure may have to
be lowered further. Each individual eye has its own optimal pressure.
Surgical treatment of glaucoma
In cases where medication alone cannot control glaucoma, there are surgical
options. Each carries its own potential risks and benefits.
- Laser surgery: Angle-close glaucoma can be cured by a procedure
called a "peripheral iridectomy". In this procedure, a laser
makes small hole in the iris to redirect fluid flow within the eye.
Open-angle glaucoma can be treated by a procedure called "argon-laser
trabeculoplasty". Here, the drainage angle of the eye is treated
precisely by a laser to help open the drainage channels. With both
procedures, recovery time is almost immediate.
- Filtering surgery: This is a micro-sugical procedure done in the
operating room under local anesthesia. A new drainage channel is made
for fluid to exit the eye and form a bubble (or "bleb")
under the conjunctiva, which is a thin membrane lining the white part
of the eye. Usually, this bleb is hidden by the upper eyelid. Recovery
time is usually 2 to 4 weeks after the procedure.
There are other options for the treatment of glaucoma, and new medications
and procedures are frequently made available.
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Open-Angle
Glaucoma