Glaucoma

Glaucoma is the name for a group of eye conditions in which the optic nerve is damaged at the point where it leaves the eye. This nerve carries information from the light sensitive layer in your eye, the retina, to the brain where it is perceived as a picture. Your eye needs a certain amount of pressure to keep the eye in shape so that it can work properly. In some people, the damage is caused by raised eye pressure. Others may have an eye pressure within normal limits but damage occurs because there is a weakness in the optic nerve. In most cases both factors are involved but to a varying extent.

What controls pressure in the eye?

A layer of cells behind the iris produces a watery fluid, called aqueous. The fluid passes through a hole in the centre of the iris (called the pupil) to leave the eye through tiny drainage channels. These are in the angle between the front of the eye (the cornea) and the iris and return the fluid to the blood stream. Normally the fluid produced is balanced by the fluid draining out, but if it cannot escape, or too much is produced, and then your eye pressure will rise.

Why can increased eye pressure be serious?

If the optic nerve comes under too much pressure then it can be injured. How much damage there is will depend on how much pressure there is and how long it has lasted, and whether there is a poor blood supply or other weakness of the optic nerve. A really high pressure will damage the optic nerve immediately. A lower level of pressure can cause damage more slowly, and then you would gradually lose your sight if it were not treated.

Are there four different types of glaucoma?

The most common is chronic glaucoma in which the aqueous fluid can get to the drainage channels (open angle) but they slowly become blocked over many years. The eye pressure rises very slowly and there is no pain to show there is a problem, but the field of vision gradually becomes impaired.

Acute glaucoma is much less. This happens when there is a sudden and more complete blockage to the flow of aqueous fluid to the eye. This is because a narrow `angle' closes to prevent fluid ever getting to the drainage channels. This can be quite painful and will cause permanent damage to your sight if not treated promptly.

There are two other main types of glaucoma. When a rise in eye pressure is caused by another eye condition this is called secondary glaucoma. There is also a rare but sometimes serious condition in babies called developmental glaucoma, which is caused by a malformation in the eye. This leaflet is about chronic and acute glaucoma.

How common is glaucoma?

In the UK some form of glaucoma affects about 2 in 100 people over the age of 40.

Are some people particularly at risk of chronic glaucoma?

Age,
Chronic glaucoma becomes much more common with increasing age. It is uncommon below the age of 40 but affects one per cent of people over this age and five per cent over 65.

Race.
If you are of African origin you are more at risk of chronic glaucoma and it may come on somewhat earlier and be more severe. So make sure that you have regular tests.

Family.
If you have a close relative who has chronic glaucoma then you should have eye tests at intervals. You should advise other members of your family to do the same. This is especially important if you are aged over 40 when tests should be done every two years.

Short sight.

People with a high degree of short sight are more prone to chronic glaucoma.
Diabetes is believed to increase the risk of developing this condition.