Eye Care - Glaucoma
Glaucoma is an 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 the retina, to the brain where it is perceived as a picture. The eye needs 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.
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, then your eye pressure will rise.
Why can increased eye pressure be serious?
If the optic nerve comes under too much pressure it can be damaged. 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.
Are there different types of glaucoma?
There are four main types.
Chronic glaucoma
The most common is chronic glaucoma (chronic = slow) 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 (acute = sudden) 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 getting to the drainage channels. This can be quite painful and will cause permanent damage to your sight if not treated promptly.
Secondary and congenital 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 congenital glaucoma which is caused by malformation in the eye.
Are some people particularly 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 the onset is somewhat earlier and more severe. So regular eye examination is recommended to monitor this.
Family
If you have a close relative who has chronic glaucoma then you should have an eye examination every year. 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 also believed to increase the risk of developing glaucoma.
Why can chronic glaucoma be a serious 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 gradually damaged. Some people do seek advice because they notice that their sight is worse in one eye than the other. The early loss in the field of vision is usually in the shape of an arc 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 forty you should have eye examinations every year and ask for a glaucoma test. There are three main 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
- doing a 'Field Test'. This involves showing a sequence of spots of light on a screen and asked to say which ones you can see.
All these tests are very straightforward, and can be done by your optometrist.
How is chronic glaucoma treated?
The main treatment for chronic glaucoma aims to reduce the pressure in your eye. Some treatments also aim to improve the blood supply to the optic nerve. You will need to go to hospital for treatment and have regular check-ups afterwards. Treatment to lower the pressure is usually started with eye drops. These act by reducing the amount of fluid produced in the eye or by opening up the drainage channels so that excess liquid can drain away. If this does not help, your specialist may suggest either laser treatment or an operation called a trabeculectomy to improve the drainage of fluids from your eye. Your specialist will discuss with you, which is the best method in your particular case.
Can chronic glaucoma be cured?
Although damage already done cannot be reversed, with early diagnosis and careful regular observation and treatment, damage can usually be kept to a minimum, and good vision can be enjoyed indefinitely.
What is acute glaucoma?
In acute glaucoma the pressure in the eye rises rapidly. This is because the periphery of the iris and the front of the eye (cornea) come into contact so that aqueous fluid is not able to reach the tiny drainage channels in the angle between them. This is sometimes called closed angle glaucoma.
What are the symptoms of acute glaucoma?
The sudden increase in eye pressure can be very painful. The affected eye becomes red, the sight deteriorates and may even black out. There may also be nausea and vomiting. In the early stages you may see misty rainbow coloured rings around white lights.