In glaucoma there is a pathological change in intraocular pressure. Nearly always, the pressure increases, causing damage to the optic nerve head and changes in the visual field.
The mean value for intraocular pressure is 15-16 mm Hg with a standard deviation of +/- 2.5. The upper limit of normal is considered to be 21 mm Hg. (Reference 12.)
Research suggests that glaucoma affects about two out of every 100 people in the UK who are over 40. The risk of glaucoma increases with age and those with a positive family history of glaucoma are at increased risk of developing glaucoma themselves. (Reference 13.)
There are four main types of glaucoma:
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open angle glaucoma (chronic glaucoma)
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acute angle closure glaucoma (acute glaucoma)
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secondary glaucoma
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developmental glaucoma (congenital glaucoma)
The most common type, which is discussed here, is open angle glaucoma.
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