Glossary

Intraocular Pressure

 This is the pressure within the eye.

A certain level of pressure within the eye is needed for the eye to keep its shape. This pressure is maintained by a balance between the producton of aqueous humour by the ciliary body and the drainage of aqueous humour from the eye through the drainge angle, into the trabecular meshwork and thence, via Schlemm's canal back into the blood stream.

Intraocular pressure is measured by tonometry and is notated in millimeters of mercury (mm Hg).

Most cases of glaucoma occur because the intraocular pressure is raised above the normal level and this leads to damage to the optic nerve in the region of the optic disc.

If a large group of people have their intraocular pressure measured the mean average of those pressures is about 16 mm Hg and two standard deviations either side of the mean give an upper level of 'normal' of about 21 mm Hg. This is, of course, a mathematical calcultion, but it correlates very well with the risks of developing glaucoma.

People under treatment for glaucoma will be receiving treatment to reduce the level of their intraocular pressure by means of eye drops, tablets laser or surgical therapy with the aim being to reduce the level of intraocular pressure to a level at which no further damage is done to the optic nerve.