What is glaucoma?
|Glaucoma is a range of conditions in which the pressure inside the eye becomes too high.|
Glaucoma is not one disorder but a range of conditions in which the pressure inside the eye becomes too high.
This results in damage to the optic nerve at the back of the eye, which can lead to loss of vision if left untreated.
Glaucoma is one of the most common causes of blindness worldwide.
How does glaucoma develop?
There is a constant flow of fluid through the eye. The flow into and out of the eye is carefully monitored in order to ensure that the eye maintains its round shape and does not become too hard or too soft.
This fluid is called the aqueous humour. It is secreted into the eye from an area behind the iris (the coloured part of the eye) and flows around through the pupil and drains out of the eye through several microscopic channels.
Glaucoma usually develops when this flow of fluid becomes obstructed and there is a build-up of pressure within the eye.
There are two main sub-groups of glaucoma.
- Primary open angle glaucoma (formerly known as chronic simple glaucoma) is a slowly progressive condition, which occurs when the tiny microscopic drainage channels gradually become blocked
- Primary angle closure glaucoma (also known as closed angle or acute glaucoma) occurs much more rapidly when the flow of fluid inside the eye cannot pass through the pupil, causing a rapid rise in pressure inside the eye.
Similar to primary open angle glaucoma, in which the nerve is progressively damaged due to raised pressure, two other conditions exist.
- Ocular hypertension occurs when the pressure in the eye is repeatedly measured as being high, and yet the eye displays no signs of glaucoma damage to the optic nerve.
- Normal tension glaucoma (normal pressure glaucoma) is the opposite, where the nerve at the back of the eye shows signs of glaucoma damage and yet the pressure is always recorded as being within normal limits.
There are other types of glaucoma, which are much rarer and can be caused by a variety of reasons:
- inflammation inside the eye (uveitis or iritis)
- the growth of new vessels inside the eye, which may occur in connection with diabetes or after blood vessel blockage at the back of the eye
- treatment with certain medicines (eg corticosteroids)
- following an eye injury
- other rare abnormalities affecting the structure of the eye.
It's rare for children to be born with glaucoma, but it's a recognised condition.
There's a tendency for this to run in families, although it may occur in children with no family history of glaucoma at all.
What are the symptoms of glaucoma?
Primary open angle glaucoma
This condition has been termed the 'silent thief of sight' – there are no symptoms until there is advanced loss of vision.
The build up in pressure in this condition is very slow. Therefore visual loss is gradual and patients often do not notice any problem until they have severe visual impairment.
There is no pain in primary open angle glaucoma.
The peripheral (or side) vision is affected first and therefore the eyesight is not obviously affected.
These peripheral areas of visual field loss increase until eventually the central vision is damaged leading to blindness.
Because primary open angle glaucoma is not usually recognised until it is advanced, people are screened for the condition as part of the optician's routine examination when eye tests are carried out.
The optician will check the pressure, examine the nerve at the back of the eye and test the field of vision if this is indicated.
As primary open angle glaucoma is rare in people under the age of 40, these screening tests are usually only carried out after this age.
Primary angle closure glaucoma
In this condition the pressure inside the eye rises rapidly and the eye becomes very painful. It is usually red and the vision becomes blurred. The patient may notice haloes around lights.
There is often significant headache and occasionally the patient feels very unwell and may even vomit.
This condition is very rare in patients under the age of 50 and is more common in people who are long-sighted. Very large cataracts can also cause this.
Other types of glaucoma
The symptoms of other types of glaucoma vary, depending on the underlying cause.
How does the doctor make a diagnosis?
Primary open angle glaucoma
If there is any suspicion of primary open angle glaucoma, the patient will usually be referred to an eye specialist (ophthalmologist).
New guidelines produced by the government (the National Institute of Clinical Excellence) advised that any patient who has been found to have a raised pressure in the eye should referred for a specialist opinion.
The specialist will examine the patient's eyes in order to accurately measure the pressure inside the eye and examine the nerve at the back of the eye for any evidence of damage. This damage is usually described as 'cupping' of the optic nerve head (or optic disc).
A detailed computerised field of vision test will also be carried out. This involves watching a blank screen and clicking a button when a light is seen.
The computer will then produce a printout of the patient’s visual field. Special scans which investigate the health of the optic nerve may also be carried out. This is very much like having a photo taken of the back of the eye.
Further tests and examinations may be required in order to ensure that there are no other reasons for the glaucoma.
Acute angle closure glaucoma
This condition is usually diagnosed quite readily because of the pain, redness and reduced vision. The pupil of the eye is dilated and the pressure inside the eye is very high.
The cornea (the clear window at the front of the eye) is usually swollen, causing the haloes round lights and blurring of vision.
This is considered to be an eye emergency and must be diagnosed and treated promptly, which requires referral to the hospital.
Other types of glaucoma
A full examination of the eye will take place in anyone who has suspected glaucoma in order to ensure that there are no other eye diseases present.
How is primary open angle glaucoma treated?
Initial treatment of glaucoma usually involves using eye drops.
There are a number of different types of eye drops that are available to treat primary open angle glaucoma:
- prostaglandin analogues
- adrenaline type drops (sympathomimetics)
- carbonic anhydrase inhibitors
- miotics (parasympathomimetics).
These drops are usually used twice a day, but once a day versions have also been produced.
They reduce the amount of fluid being secreted into the eye.
Timolol (Timoptol) is an example of a beta-blocker.
These drops are used once a day in the evening. They work by increasing the drainage of fluid out of the eye.
The best recognised side-effect of this type of eye drop is that it can change the colour of the eye, and in addition can cause a thickening of eye lashes.
A newer drop called tafluprost (Saflutan)is also a prostaglandin analogue but is preservative free, and it's therefore useful for patients who become allergic to preservatives in the drops.
Lumigan is also now available in preservative free form.
Adrenaline-type drops (sympathomimetics)
These are used twice a day and are generally well tolerated. They reduce the amount of fluid secreted into the eye.
Patients with heart disease may be unsuitable for this treatment.
Carbonic anhydrase inhibitors
These drops are used twice a day if used with beta-blockers, or three times a day if used alone. They reduce the secretion of fluid into the eye.
Dorzolamide (Trusopt) is an example of a carbonic anhydrase inhibitor.
These drops are usually used four times a day. They increase the drainage of fluid out of the eye.
These drops cause a small pupil, which may mean that they cause a reduction in vision.
They may give rise to headache. These drops were the original drops to be used for glaucoma but are now less commonly used because of the other newer drops as outlined above.
Pilocarpine (eg Pilogel) is an example of a miotic (parasympathomimetic).
Carbonic anhydrase inhibitor tablets
In some cases these tablets are prescribed, but this is usually only as a temporary solution because they can have many side-effects – such as general nausea, tiredness, tingling of the fingers and, occasionally, if used for a long time, a tendency to cause kidney stones.
Acetazolamide (Diamox) is an example.
This treatment is used to increase the flow of fluid from the eye. The effect of this treatment may only be temporary and therefore may not be suitable as a long-term solution.
Many patients have surgery to treat glaucoma. The operation used (trabeculectomy) allows drainage of fluid from inside the eye to the outside of the eye.
This type of surgery usually results in a small 'blister' on the eye, which is usually positioned under the upper eyelid. The fluid is gradually absorbed by the blood vessels which cover this 'blister'.
Additionally, certain types of glaucoma may require a tiny valve to be inserted into the eye to help drain out the excess fluid which is causing the pressure to rise. This may also be used if trabeculectomy has been unsuccessful.
These types of surgery may include the use of anti-metabolite medicines that reduce the risk of scarring, in order to make the success of the operation higher, although this may also increase the potential for complications.
Complications of such surgery include transient reduction in vision after the operation, but this usually recovers. There is a long-term risk of infection that must always be considered.
How is closed angle or acute angle closure glaucoma treated?
Treatment in this condition needs to be rapid. It takes the form of drops, medicines given intravenously and orally, laser surgery and sometimes surgical treatment.
Systemic medicines (carbonic anhydrase inhibitors)
As the pressure is very high inside the eye, this needs to be dropped rapidly and therefore medicines, such as acetazolamide, are given rapidly into the circulation through a vein. This should reduce the pressure quite quickly.
A hole in the coloured part of the iris is essential in order to prevent this condition happening again. This hole is usually made using a laser.
Both eyes need to be treated, as although only one eye is usually affected, the other eye will go on to develop acute closed angle closure if left untreated.
Sometimes all the above treatments do not allow control of the pressure and therefore a trabeculectomy (as outlined above in primary open angle glaucoma) may be required.
How are other types of glaucoma treated?
A combination of drops, laser treatment and/or surgery may be required depending upon the type and stage of glaucoma.
Glaucoma, if not treated appropriately or picked up early enough, may lead to blindness.
What can be done to avoid glaucoma?
Primary open angle glaucoma
There are no known methods of preventing this condition, but it is vital that people over the age of 40 have their eyes regularly examined because treatment in the early stages may prevent visual loss.
It's impossible to regain damaged vision if the early stages are missed.
People with a family history of glaucoma (especially parents or brothers and sisters) should be especially vigilant, but anyone over the age of 40 should have a regular eye examination carried out by their optometrist as part of the sight test.
Acute angle closure glaucoma
The acute attack with pain and reduction in vision may be preceded by similar less severe attacks in the past.
There may be a history of haloes seen round lights, particularly in the evening, which tend to settle overnight when the affected person goes to sleep. People with such symptoms should seek medical advice.
Other types of glaucoma
Your eye specialist (ophthalmologist) may have given warning that you are more susceptible to glaucoma if you suffer from one of the conditions listed above.
Future developments in glaucoma
As glaucoma can potentially cause significant, irreversible visual loss, doctors and scientists are continually doing research to minimise the risk of this happening.
Methods of continually measuring the pressure in the eye are being investigated, such as contact lenses which check the pressure at various intervals throughout the day.
This would allow doctors to have a more accurate assessment what the patient’s pressure is actually doing, and may lead to fewer clinic visits for patients.
Research into finding drops which are more effective in lowering pressure is a particular priority.
One such group is the Rho Kinase (ROCK) inhibitors, which act to improve outflow of the fluid inside the eye, and also protect the optic nerve by maintaining its blood circulation. These show promise but are not yet available.
Methods which allow medication to be delivered slowly into the eye, such as a special contact lens, are also being investigated, as this would reduce the need for patients to put in many drops over the course of the day.
Exciting new surgical techniques known as ‘minimally invasive glaucoma surgery’ (MIGS) are playing an increasingly important role in the treatment of glaucoma.
MIGS devices can be implanted in the natural drainage portion of the eye and aid fluid drainage. These are often implanted at the same time as a cataract operation is carried out, but may in future be used in isolation.
If picked up early enough, the vision should remain good and there should be no restrictions in activity.
There are strict guidelines regarding visual standards for driving, and people with glaucoma are advised to let the DVLA know about the diagnosis. They will require regular fields of vision testing to ensure that they remain fit to drive.
After surgery there may be limitations on activities in the short term.
Tips to manage glaucoma
- Use all medication exactly as prescribed by your ophthalmologist.
- Ensure that all follow-up appointments are kept.
- Make sure that you are clear about what type of glaucoma it is that you have.
- Let your family know so that they should go and be screened for the disease.
- If you need to start any new tablets for other conditions, make sure your doctor is aware that you are using eye drops and what they are.
- Always include your eye drops if you are asked about the medications that you take regularly.
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Assessing your vision: eye tests are important health examinations.
How to keep your eyes healthy: use this guide to keep your eyes looking good.
Based on a text by Dr Caroline MacEwen, consultant ophthalmologist
Last updated 13.09.2013