glaucoma

n.

a condition in which loss of vision occurs because of an abnormally high pressure in the eye. In most cases there is no other ocular disease. This is known as primary glaucoma and there are two pathologically distinct types: acute and chronic simple. In acute (or angle-closure) glaucoma, there is an abrupt rise in pressure due to sudden closure of the angle between the cornea and iris where aqueous humour usually drains from the eye. This is accompanied by pain and marked blurring of vision associated with inflammation of the anterior segment. In the more common chronic simple (or open-angle) glaucoma, the pressure increases gradually, usually without producing pain, and the visual loss is insidious. The same type of visual loss may rarely occur in eyes with a normal pressure: this is called low-tension glaucoma. Primary glaucoma occurs increasingly with age and is an important cause of blindness. Secondary glaucoma may occur when other ocular disease impairs the normal circulation of the aqueous humour and causes the intraocular pressure to rise.

In all types of glaucoma the eventual problem is to reduce the intraocular pressure. Drops are inserted into the eye at regular intervals to improve the outflow of aqueous humour from the eye and/or to reduce the production of aqueous humour. Drugs used for this purpose include beta blockers (e.g. timolol, levobunolol, carteolol), carbonic anhydrase inhibitors (e.g. brinzolamide, dorzolamide), alpha-receptor stimulants (e.g. apraclonidine, brimonidine), and prostaglandin analogues (e.g. latanoprost). If this treatment is ineffective, surgery may be performed to make a new channel through which the aqueous humour may drain from the eye in sufficient quantities to allow the pressure to return to normal. Such operations are known as drainage or filtering operations.