Eye Disease
Glaucoma
Surgery
Glaucoma comprises a group
of eye diseases in which the pressure inside the eye
(the intra-ocular pressure) causes damage to the nerve
at the back of the eye (the optic nerve). This can result
in a progressive loss of peripheral side vision (the
visual field) and ultimately can cause complete blindness.
In the majority of cases the intra-ocular pressure is
raised. In some eyes, however, the pressure may be within
normal limits, but damage still occurs because of weaknesses
of the optic nerve.
Fluid (aqueous humour) is produced inside the eye by
a layer of cells on the muscle (the ciliary body) that
moves the lens in the eye. The fluid is needed to provide
nutrients to the front of the eye (especially the cornea
and lens that have no blood vessels), to remove waste
products from these structures and to create a pressure
within the eye to maintain its shape and allow it to
function correctly. The aqueous fluid drains mainly
through a structure called the trabecular meshwork that
lies in the angle where the cornea meets the iris. The
normal pressure in the eye is between 12 and 21 millimeters
of mercury (mmHg). If for any reason the outflow of
aqueous fluid is obstructed the pressure can rise and
glaucoma may occur.
There are two main types of glaucoma:
• Closed-Angle - where the angle between the peripheral
cornea and iris becomes closed
• Open-Angle - where this angle is open
Both types may occur either spontaneously
(primary glaucoma) or as a result of another eye condition
(secondary glaucoma).
Closed-angle glaucoma is relatively uncommon in the
UK and Western countries. It tends to affect those who
are very long-sighted. It is more common in the elderly
and oriental races. It can run in families. Typically
symptoms are acute and severe, the eye suddenly becoming
very red and painful, with accompanying nausea and vomiting.
The pressure in the eye is usually very high and the
vision extremely blurred. Occasionally it may not present
with an acute severe attack, but with a series of mild
episodes characterized by eye ache and the appearance
of misty rainbow coloured rings around lights. These
typically occur in the evening, when the pupil of the
eye has become dilated in the dark, precipitating the
attack.
Acute closed-angle glaucoma is
an ocular emergency, requiring prompt treatment in hospital
with eye drops and tablets to reduce the pressure and
prevent the eye from going blind. Once the attack has
been controlled laser surgery, called a YAG laser iridotomy,
is required to make a hole in the outer border of the
iris, to relieve the obstruction and prevent further
episodes. This laser treatment is not painful. Usually
the other eye is also treated because there is a high
risk that it will develop the same problem. With prompt
treatment there is usually good recovery of vision.
Delay may cause a permanent loss of sight. Occasionally
the eye pressure may remain raised, despite treatment
and further surgical measures may be necessary.
Open-Angle glaucoma is more common and affects 2% of
adults over 40. It is more frequent with increasing
age (affecting 4% of those over 65), in African races,
in those who are very shortsighted and those with diabetes.
Its exact cause is unknown. Although the drainage angle
is open and appears normal to examination, an increased
resistance to aqueous outflow at the trabecular meshwork
has been found. This resistance to drainage causes the
pressure to rise, resulting in damage to the optic nerve,
possibly by direct mechanical compression or a reduction
of its blood supply.
Open-angle glaucoma is typically
a chronic, insidious disease, affecting both eyes. Damage
to the optic nerve causes a slow loss of peripheral
(side) vision. The danger of this condition is that
the eye seems perfectly normal and the loss of vision
is so gradual and painless that people are often unaware
of its presence until damage is extensive and permanent.
The early loss in the field of vision in glaucoma is
typically in the shape of an arc a little above or below
the centre. If untreated the field loss progresses until
most of the peripheral side vision is lost and only
a small central "tunnel" of vision remains.
Eventually, with progression, this too can be lost causing
complete blindness.
As it tends to run in families
and most patients have few or no symptoms, it is important
to have eye pressure checked regularly, especially if
there is a family history of glaucoma.
The main treatments are aimed at lowering the pressure
within the eye. This can be achieved either by reducing
the amount of aqueous fluid produced or opening up the
channels by which fluid leaves the eye. Treatments may
be:
• MEDICAL - using eye-drops
or tablets
• LASER
• GLAUCOMA
SURGERY
In most cases treatment usually
starts with eye-drops. If this does not succeed then
either laser or surgery is offered.
