Glaucoma
What Is Glaucoma?
Glaucoma is a name given to a group of conditions,
which damage the optic nerve at the point it reaches the retina.
What Are The Symptoms?
In the most common type of glaucoma (Chronic
Open Angle) there are no symptoms. The less common form (Acute Closed
Angle) has symptoms such as red eyes, pain, nausea, halos and blur.
What
Is The Difference Between The Two Types?
The
two types differ in many key aspects. The table lists some of the
main differences: |
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CHRONIC OPEN ANGLE |
ACUTE CLOSED ANGLE |
| Onset |
Comes
on very gradually and progresses slowly |
Comes on very suddenly and progresses
rapidly |
| Incidence |
More
Common |
Rarer |
| Caused By |
Either
raised fluid pressure or compromised blood flow to the optic
nerve head |
Blockage
of the drainage mechanism, causing fluid pressure to build up |
| Risk Factors |
Increasing
age
An immediate family member with it
Afro Carribean and Asian Ethnicity
Diabetes
Severe shortsightedness - the nerve support is more fragile
as the eyeball is longer than normal
Certain medications |
Small drainage channels
Small eyes, as occur in very severely long sighted individuals |
| Symptoms |
None,
until the late stages. In advanced glaucoma there will be an
awareness of missing areas (dark holes) in the visual field |
Red
eyes, severe pain, nausea, halos and blur |
| Effect on Vision |
A
gradual and slow loss of sight if not treated in time. Vision
loss will vary from small to very large blind spots. In very
advanced stages, only a small area of central vision remains,
and the effect is a bit like looking down a tunnel |
A
rapid loss of sight if not treated immediately. Vision loss
is both central and peripheral |
| Pressure Readings |
Can
be low, normal or high |
Are
always very high |
| Treatment |
Usually
drops to reduce the amount of fluid produced and or increase
the amount that drains out |
Usually
surgery. An artificial drainage channel is created by making
a small hole in or near the iris, using a laser or blade. |
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How Is Glaucoma Detected?
There
are a number of tests for Open Angle Glaucoma, and it is the combined
information from all of them that determines whether it is present
or not. The commonest ones are:
Opthalmoscopy:
the optometrist examines the physical appearance of the nerve head
for signs of disease.
Nerve Head Photography:
Compares the appearance of the nerve from one visit to the next.
Pressure Measurement:
the eyes internal fluid pressure is measured
Visual Fields:
checks for the presence of abnormal blind spots
Newer tests include:
Ocular Coherence Tomography:
a laser measures the thickness of the nerve layer to check for tissue
loss
Pachymetry:
Measures the thickness of the cornea as this has a bearing on whether
the pressure reading is acceptable
Closed Angle Glaucoma, because it is much less common, is not routinely
tested for. If signs or symptoms suggest its presence then the following
specialist test is done:
Gonioscopy:
The drainage area is examined to assess the quality of the drainage.
If the structures appear compromised, preventative surgery may be
indicated.
Do All the Tests
Need to Be Done or Just The Pressure Test?
The pressure test alone is not sufficient to
check for glaucoma. This is because in many glaucoma cases the pressure
is not particularly high. In this type of glaucoma, known as Normal
Tension Glaucoma, the pressure reading is within the ‘normal
range’ but is too high for that particular individual.
Other individuals can have relatively high pressures, but it never
causes any damage. These people are classified as having Ocular Hypertension.
There is still much unknown about glaucoma, but recent research has
suggested that glaucoma is not just caused by abnormal eye pressure,
but a combination of yet unknown other factors.
Further Information:
More information on Glaucoma is available by clicking these links:
http://www.rnib.org.uk/xpedio/groups/public/documents/PublicWebsite/public_rnib003655.hcsp
http://www.glaucoma-association.com/nqcontent.cfm?a_id=176
http://www.nhsdirect.nhs.uk/articles/article.aspx?articleid=175
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| Optic Nerve With Glaucoma |
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