Glaucoma is one of the most common causes of blindness. It is due to an increase in the pressure of the fluid which circulates inside our eyes. This increased pressure eventually damages the optic nerve which carries the 'picture' seen by the eye to the brain.

There are several types of glaucoma, each having a different cause and requiring different treatment.

The eye has 2 chambers, separated by the lens. Fluid is made in the posterior (rear) chamber, circulates around the lens and passes through the pupil into the anterior (front) chamber from where it drains away. A blockage in the flow of this fluid results in glaucoma. Such blockages may occur suddenly, causing acute glaucoma, or develop slowly and produce the chronic form of the disease.

Acute glaucoma causes a painful red eye, blurred or 'foggy' vision, with 'haloes' around lights, often accompanied by nausea and vomiting.

Chronic glaucoma causes a gradual loss of vision, starting with the peripheral (side) vision.

Once detected, glaucoma can be treated, preventing further damage and loss of sight. Treatment usually means the regular use of eye drops, although surgery is sometimes necessary to release the blockage.

Glaucoma is more common with age (of those people over 65 years old, one in 20 is affected) and in those with close relatives who have the disease. Simple testing, which is painless, can detect increased pressure and should be done regularly as we get older.

If you have a suddenly painful red eye with disturbed vision, see a doctor immediately. If you have noticed a gradual worsening or foggy vision, can't see things to the side of you, or notice coloured rings around a light when you look at it, see a doctor soon.