Glaucoma

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Glaucoma

Glaucoma

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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 eyeball 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.

Eye pressure is largely independent of blood pressure.

Causes


What controls pressure in the eye?

A layer of cells behind the iris (the coloured part of the eye) produce 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 if too much is produced, then your eye pressure will rise. (The aqueous fluid has nothing to do with tears).

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 is not treated.

Types of Glaucoma


There are four main types of glaucoma:

Chronic 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: Acute glaucoma is much less common in western countries. 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.

Secondary and developmental glaucoma: 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 potentially serious condition in babies called developmental or congenital glaucoma which is caused by malformation in the eye.

 

Chronic Glaucoma


Are some people more at risk of chronic glaucoma?

Yes. There are several factors which increase the risk.

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 an eye test at regular 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 year.

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.

Why can chronic glaucoma be a risk to sight?


The danger with chronic glaucoma is that your eye may seem perfectly normal. There is no pain and your eyesight will seem to be unchanged, but your vision is being damaged. Some people do seek advice because they notice that their sight is less good in one eye than the other.

The early loss in the field of vision is usually in the shape of an arc a little above and / or below the centre when looking ‘straight ahead’. This blank area, if the glaucoma is untreated, spreads both outwards and inwards. The centre of the field is last affected so that eventually it becomes like looking through a long tube, so-called ‘tunnel vision’. In time even this sight would be lost.

How is chronic glaucoma detected?


As glaucoma becomes much more common over the age of 40 you should have eye tests at least every two years and ask for all three glaucoma tests. This has been shown to be much more effective in detecting glaucoma than just having one or two of the tests. These tests are:

  • viewing your optic nerve by shining a light from a special electric torch into your eye

  • measuring the pressure in the eye using a special instrument

  • being shown a sequence of spots of light on a screen and asked to say which ones you can see


All these tests are very straightforward, don’t hurt and can be done by most high street optometrists (opticians).
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