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The intraocular pressure is critical to the normal
functioning of your eye. If the pressure is too low, the eyeball
deflates and folds form in the retina blurring the vision. If the
pressure is too high the optic nerve fibers become compressed and
eventually die. The death of these cells results in permanent visual
loss.
A circular pump inside the eye called the ciliary
body produces fluid (aqueous). The aqueous circulates inside the eye and
returns to the blood stream through a meshwork. This is situated in a
ring extending right around the junction of the iris and cornea (called
"the angle"). The meshwork provides some resistance to the
flow of aqueous, so the pressure in the eye is maintained. If the
resistance to flow increases in the meshwork, the intraocular pressure
builds up. Aqueous fluid also drains out of the eye through the ciliary
body and sclera (uveo-scleral outflow).
The intraocular pressure is measured as millimeters of mercury (mm Hg).
The normal eye usually has a reading between 12 and
20 mm Hg.
A number of things can happen to interfere with the
normal flow of the aqueous. This can result in a build up of pressure.
Understanding what kind of obstruction is occurring in a particular eye
allows the ophthalmologist to identify which mechanism is causing the
raised pressure and, if needed, to plan a particular course of
treatment.
The most common cause of raised pressure is a
malfunction in the trabecular meshwork - it simply does not drain the
aqueous as efficiently as it should. Pressure rises slowly and may not
cause damage to the actual eye structure for many years. What can
happen, though, is that the increased pressure begins to interfere with
the delicate nerve cells at the back of the eye, which convert light
energy into nervous impulses and transmit them to the part of the brain
which is responsible for sight.
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