What is 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 back of 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, damage to the optic nerve is caused by abnormally high eye pressure. Some people may have eye pressure within normal limits but damage occurs because of a weakness in the optic nerve structure. In most cases, both of these factors are involved but to a varying extent. Eye pressure is largely independent of blood pressure.
What controls the pressure in the eye?
A layer of cells behind the iris (the coloured part of the eye) 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 bloodstream. 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. (The aqueous fluid has nothing to do with tears). See right.
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 been present, also whether there is a poor blood supply or other weakness of the optic nerve. 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?
Yes. There are four main types.
The most common is chronic or open-angle 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 or discomfort to indicate a problem, but the field of vision gradually becomes impaired.
Acute glaucoma (acute = sudden) is much less common in the western hemisphere. This happens when there is a sudden and more complete blockage to the flow of aqueous fluid from the eye. This is because a narrow `angle’ closes to prevent fluid ever getting to the drainage channels. This type of glaucoma is normally 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.
How common is glaucoma?
In the UK some form of glaucoma affects about 2% of people over the age of 40 but the risk increases significantly with age increasing to 15% of people over 80. This means there are over 500,000 who suffer in the UK. Unfortunately, only 250,000 of these people have actually had their glaucoma detected. Hence the importance of having regular eye examinations as you get older.
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 2% of people over 40, 5% of people over 65 and 15% of people over 80.
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 regular eye examinations. You should advise other members of your family to do the same. This is especially important if you are aged over 40 when you should have an eye examination at least annually. Indeed the NHS makes provision for all near relations of glaucoma suffers to have their eyes examined annually. To check NHS eligibility for eye examinations – click here.
Short sight. People with a high degree of short sight are more prone to chronic glaucoma.
Diabetes increases 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 or discomfort and your eyesight will seem to be unchanged, but your peripheral vision is being damaged making it difficult to see things in certain parts of the margins of your vision. Some people do seek advice because their sight is often 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 horizon when looking `straight ahead’. This blank area, if glaucoma goes untreated, spreads both outwards and inwards. The centre of the field (where sharp reading vision occurs) is the last area 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?
There are several tests which when all are performed can help to detect glaucoma at the earliest stage. These tests are:
- viewing your optic nerve by shining a light from a special electric torch called an ophthalmoscope into your eye.
- measuring the pressure in the eye using a special instrument called a tonometer. Often this instrument ‘puffs’ a jet of air on the eyes.
- you use an instrument called a ‘visual field analyser’ which shows a sequence of spots or flickering lines of light on a screen and you are asked to indicate which ones you can see by pressing a button.
- 3DOCT EyeScan (Optical Coherence Tomography) is the latest instrument that can detect damage to the optic nerve fibres which occur in glaucoma.
You have access to all these tests at Paul Whiteman Optometrists, they are very straightforward although there is a fee involved in having some of them performed.
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 of the optic nerve. You will need to go to the 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.
Can chronic glaucoma be cured?
Damage already done cannot be repaired, 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 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 blackout. There may also be nausea and vomiting. In the early stages, you may see misty rainbow coloured rings around white lights.
Is acute glaucoma always severe?
Sometimes people have a series of mild attacks, often in the evening. Vision may seem `misty’ with coloured rings seen around white lights and there may be some discomfort in the eye. If you think that you are having mild attacks you should contact your optometrist without delay. In the routine eye examination, the structure of the eye may make the optometrist suspect a risk of acute glaucoma and advise further tests.
What is the treatment?
If you have an acute attack you will need to go into hospital immediately so that the pain and the pressure in the eye can be relieved. Drugs will be given which both reduce the production of aqueous liquid in the eye and improve its drainage.
An acute attack, if treated early, can usually be brought under control in a few hours. Your eye will become more comfortable and sight starts to return. When the pain and inflammation have gone down, your ophthalmic surgeon will advise making a small hole in the outer border of the iris to relieve the obstruction, allowing the fluid to drain away. This is usually done by laser treatment or by a small operation.
Usually, the surgeon will also advise you to have the same treatment on the other eye, because there is a high risk that it too will develop the same problem. The treatment is not painful. Depending on circumstances and the response to treatment, it may not require admission to the hospital. Sometimes a short stay in hospital may be advised.
Will I be able to drive with glaucoma?
If you are diagnosed with glaucoma you must inform the Driver and Vehicle Licensing Authority (DVLA). Most people can still drive if the loss of visual field is not advanced. To assess possible damage to your peripheral vision you will be asked to take a special visual field test to see whether your sight meets the DVLA standards. Paul Whiteman Optometrists are registered to perform this special test on behalf of the DVLA. The IGA Eyeway Code about driving may also be helpful.
What if my sight cannot be fully restored?
Early detection and treatment will usually prevent or retard further damage by glaucoma. Much can be done to help you use your remaining vision as fully as possible. You should ask your optician or optometrist about low vision aids and whether you are eligible to register as partially sighted or blind. Registration opens the door to expert help and sometimes to financial benefits.
Further help and information
The International Glaucoma Association supports patients by providing information so that they can cooperate fully in their treatment and prevent sight loss. It also promotes awareness and early detection of glaucoma and supports and carries out research. The International Glaucoma Association (IGA), 108c Warner Road, Camberwell London SE5 9HQ Telephone 0207-737 3265 Available for advice by letter or by telephone 10 am – 5 pm from Monday to Friday.
The Partially Sighted Society offers information and advice, publications, aids to vision, enlargement services and local support to help you make the most of your vision. Contact: The Partially Sighted Society, The Sight Centre 9 Plato Place, 72-74 St Dionis Road, London SW6 4TU. Telephone 0207 371 0289.