A condition in which loss of vision occurs because of damage to the optic nerve, which in most cases is caused by an abnormally high pressure in the eye. This is known as primary glaucoma and there are two distinct types. In acute (or closed-angle) glaucoma, there is an abrupt rise in pressure due to sudden closure of the angle between the cornea and iris where aqueous fluid usually drains from the eye.

This is accompanied by pain and marked blurring of vision. 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 some other eye disease impairs the normal circulation of the aqueous fluid and causes the pressure inside the eye to rise.

In all types of glaucoma treatment is focused on reducing the pressure inside the eye. Drops are instilled into the eye at regular intervals to improve the outflow of aqueous fluid from the eye and/or to reduce the production of aqueous fluid. Drugs used include some beta blockers; miotics, such as pilocarpine and carbachol; adrenaline and drugs with similar effects to adrenaline; the sympathomimetic drugs apraclonidine and brimonidine; and the prostaglandin analogue latanoprost. Carbonic anhydrase inhibitors, in the form of tablets or eye drops, are also used.