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Glaucoma |
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Glaucoma is the result of impaired resorption
of circulating aqueous, leading to increased pressure in the globe and damage to
the retina
A very common syndrome in which there is increased intraocular pressure,
glaucoma affects 2% of the population over the age of 40 years. It is important
in that if it remains untreated, blindness develops.
There are two main clinical syndromes.
Chronic glaucoma occurs with gradual
increase in intraocular pressure, leading to slow, gradual deterioration in
visual acuity if untreated. Acute glaucoma is associated with rapid increase in
intraocular pressure, which causes severe pain and redness in the eye, and rapid
deterioration in visual function (this can be permanent if not urgently
treated).
The effects of raised intraocular pressure are cupping of the optic disc,
detected on fundoscopy, and degeneration of retinal ganglion cells. Clinically,
there is progressive peripheral visual-field loss, leading to blindness in
untreated cases. In acute glaucoma there is breakdown of the endothelium,
leading to oedema of the cornea and formation of painful corneal bullae. In
chronic glaucoma the sclera may stretch to form bulges termed staphylomas.
Glaucoma is caused by the failure of filtration of aqueous by the trabecular
meshwork
There are several common causes of glaucoma, divisible into primary and
secondary groups.
Primary glaucoma is caused by two main abnormalities in drainage of aqueous:
1 Closing up of the trabecular meshwork, which normally leads to the canal of
Schlemm, can occur as a degenerative process, the incidence of which increases
with age; it is mainly encountered in those over the age of 40 years, often
being familial. Because the drainage angle is normal, this is termed primary
open-angle glaucoma.
2 With age, patients who have a congenitally shallow anterior chamber develop
narrowing of the angle between the iris and the cornea, causing functional
blockage to aqueous drainage. This occurs particularly when the pupil is
dilated, as the iris thickens with
contraction. Acute attacks may therefore be precipitated by being in the dark.
Because the drainage angle is abnormal, this is termed primary closed-angle
glaucoma. Secondary glaucoma is caused by diseases that obstruct the drainage of
aqueous. For example, there may be adhesions between the iris and cornea that
are caused by uveitis or are secondary to vascular proliferation due to retinal
ischaemia(secondary closed-angle glaucoma). Alternatively, there may be blockage
of the trabecular meshwork by particulate material in the aqueous, especially
degenerate lens material, pigment from melanocytic lesions, or macrophages
accumulating in response to haemorrhage or inflammation (secondary open-angle
glaucoma).
Congenital glaucoma, seen in childhood with enlargement of the globe, is very
rare. It is mainly due to developmental defects in the drainage of aqueous.
Normal filtration of aqueous by the trabecular network. With age, the channels
in the trabecular meshwork degenerate. However, aqueous continues to be
produced, so the pressure in the eye increases. As the angle between the cornea
and iris root is normal (open), this is termed open-angle glaucoma. If the
anterior chamber is congenitally shallow, then the drainage angle is
functionally closed. When the pupil dilates, for instance in low light, this
further compromises the drainage of aqueous and may precipitate an acute attack
of glaucoma. If abnormal tissue (e.g. new blood vessels) blocks the trabecular
meshwork, then aqueous cannot drain and glaucoma may develop; this is termed
secondary closed-angle glaucoma. If particulate matter (such as inflammatory
cells) occludes the trabecular meshwork, it is termed secondary open-angle
glaucoma, since the irido-corneal angle remains open. |
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We give here simplified and accurate information about the disease
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