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The
term 'glaucoma' covers several different conditions. The most common is
chronic (primary open angle) glaucoma - this form usually affects both
eyes and develops slowly so that loss of sight is gradual. There is no
pain, redness of the eye or dramatic change in vision.
With acute (angle closure) glaucoma, there is a sudden increase in the
pressure within one eye. The eye becomes red and painful. Often there
is mistiness of vision and episodes of seeing haloes around lights.
Sometimes, other diseases of the eye cause a rise in the pressure within
the eye - this group of conditions is called secondary glaucoma.
Congenital glaucoma (buphthalmos) is a condition where glaucoma is present
from birth. An increase in the pressure within the eye causes it to enlarge.
The contents of the eyeball are nourished by a fluid called aqueous humour,
which is different to tears. It is secreted within the eye by a tissue
called the ciliary body, and leaves the eye via another tissue, called
the trabecular meshwork. This 'meshwork' is situated at the back of the
eye.
An increase in the pressure within the eye usually happens because there
is an obstruction within the trabecular meshwork. The obstruction means
that the aqueous within the eye is not drawn out, although it continues
to be produced. There is a build up of fluid in the eye, which increases
the pressure.
This increased pressure pushes on the back of the eye, which damages the
optic nerve. The optic nerve carries signals to the brain from the eye,
and when this is damaged, it causes irreparable sight loss.
Glaucoma is one of the world's leading causes of blindess. In the UK,
1 in 50 people over 40 have this condition. Glaucoma is not curable, but
blindness is preventable if the glaucoma is diagnosed and treated early
enough.
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