Glaucoma
Introduction: In the US glaucoma is the second most common
reason for loss of eye sight (right after macular degeneration, which is the most
common reason). There are about 2 million Americans who have glaucoma, but only
about 50% know about it. It can hit at any age group, although it is more common
in the older age group. Among younger glaucoma patients some inherited forms
of glaucoma are found more often or there was prior injury to the affected eye
leading to internal scarring. Of those who have high intraocular pressure (=IOP)
only 1% per year will develop glaucoma. There are two forms of glaucoma, the open-angle
glaucoma found in about 70% of glaucomas and the angle-closure
glaucoma, which occurs in about 10% of all cases. The remaining
20% are more difficult to classify. Usually glaucoma develops from a blockage
of the Schlemm's
canal, which is shown in the above link (two forms of glaucoma).
The eye fluid has no normal way of drainage when this happens and this will raise
the IOP in most , but not all cases. In about 85% of glaucoma cases the IOP will
be elevated. But in about 15% of glaucoma patients the IOP is normal when the
IOP is measured. An ophthalmologist will, however, do 4 tests that will determine
whether or not the patient has glaucoma: - Thorough eye examination
including gonioscopy
- IOP
measurement
- visual field examination
- examination of optic discs
(using slit lamp)
Only when all these four parameters are examined
can the eye specialist tell whether there is glaucoma present that needs to be
treated.
Otherwise
glaucoma could be missed or get overdiagnosed. Here are two examples: a normal
or low-pressure glaucoma patient could be overlooked, if only the
IOP is measured. This patient would wrongly miss treatment for glaucoma, which
would lead to blindness on that eye from optic nerve atrophy. Another example
is a patient who has elevated IOP (ocular
hypertension) and who would be falsely
classified as having glaucoma, if only the IOP would be measured.
In this case the other 3 examination methods would rule out glaucoma and the correct
diagnosis would be "ocular hypertension". 90% of patients with ocular
hypertension (IOP more than 21 mm mercury) will not develop glaucoma and simply
need regular follow-up exams for monitoring. On the other hand, if these patients
develop IOP's of greater than 28 mm mercury, many eye specialists would start
treating these patients with eye drops to lower the IOP, as these patients likely
were in the early stages of glaucoma development.
There are high risk groups
who develop open-angle glaucoma as is summarized in this table.
| Common causes of open-angle
glaucoma | | Family
history | diabetes |
| older age | high
blood pressure | | elevated
IOP | conditions that requires chronic use
of systemic corticosteroids | | black
race | Myopia (shortsightedness) |
Signs and symptoms of glaucoma: Unfortunately
there are no early signs and symptoms for glaucoma. Late symptoms are loss
of the visual fields in the sense of missing words or lines when reading or missing
stairs when the lower visual field is missing. This can cause accidents when driving
a car. First the vision in the periphery tends to be affected, later central vision
is affected. Other symptoms can be blurred vision and intermittent eye pain. Diagnostic
tests: As already indicated the eye specialist will do a thorough eye
examination including gonioscopy
and measurements of the intraocular pressure (IOP) where one of the methods is
the Goldmann tonometry. In addition, as mentioned above, the
specialist will also do visual
field examinations and do slit
lamp examination to inspect the optic
disc. Treatment
of glaucoma: Both surgical glaucoma procedures will restore the
normal drainage of the internal eye fluid, which in turn takes the pressure off
the optic nerve. In most open-angle glaucoma patients laser
surgery can be done by an eye surgeon equipped to do that procedure.
Conventional surgery is retricted to those cases where the specialist cannot use
laser surgery. Here is another site where glaucoma
surgery is described. Prevention of glaucoma: To
prevent glaucoma, it is important to be examined from age 30 onwards every 2 or
3 years with a complete eye examination by an eye specialist, more often in high
risk families where glaucoma is inherited. This way early changes can be seen
and treated right away with laser surgery. High risk people as indicated in the
table above must be carefully checked and followed frequently. |
