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Glaucoma - Health Information

Health Information

What is glaucoma

Glaucoma is a condition affecting the eye, where pressure of fluid inside the eye increases above the normal level and affects vision. The progression of the disease may lead to destruction of the nerve fibre and impaired vision in later life.

How does it occur

The eye is approximately the size of a ping-pong ball and its walls are composed of several layers of muscles. The innermost layer of this wall is called the retina and is light sensitive, being responsible for detecting light rays and sending them to the brain via the optic nerve which transmits the light in the form of electric impulses. This helps to establish vision.

Inside the eyeball is a lens suspended by muscles near the front of the eye and this focuses incoming light rays from outside onto the retina. In front of the lens is the iris which, by alteration of its diameter, controls the amount of light entering the eye.

The eyeball is filled with jelly like fluid which fills the inside of the eyeball and gives the eye its shape and tension. The fluid between the lens and the front of the eye is known as aqueous humour and fills the area known as the anterior chamber whilst the remainder of the eye behind the lens is known as the posterior chamber and the contents known as vitreous humour.

This liquid is constantly being produced by cells in the eye and is drained away through a drainage channel. Thus the constant flow of liquid maintains a constant pressure in the eyeball called the intraocular pressure and in health is between 15 and 20 mm mercury.

If there is an excessive production or an inadequate drainage of fluid the pressure will rise abnormally high to a point where vision is affected. This is glaucoma.

Glaucoma affects more than 1% of the general population over 40 years. The incidence increases with age up to 3% over 70 and is one of the major causes of registerable blindness in the UK.

Why does it happen

In glaucoma, for reasons not quite known, the thin fluid does not drain as quickly as it should. When this happens the fluid backs up and puts pressure on the delicate optic nerve which can then become damaged. At first, the increased fluid pressure damages only those nerve cells and fibres that control "side vision". As a result this peripheral vision is destroyed.

In the final stages of the disease, the pressure destroys the fibres which permit central vision resulting eventually in total loss of vision. If caught early the damage may be slight and both medical and surgical treatments exist which can stop progression of the disease. The amount of pressure it takes to cause damage varies from person to person and that is why individual screening is important.

Who is at risk

  • The chance of developing glaucoma increases with advancing age
  • It tends to run in families
  • Diabetics are at higher risk
  • patients who have suffered eye injury or had eye surgery are at risk of this complication
  • Glaucoma is more common in Afro-Americans

What are the symptoms

Glaucoma occurs in two forms, namely acute and chronic:

Acute Glaucoma: In this case there is a sudden blockage of the duct that drains the aqueous fluid at the front of the eye resulting in an abrupt rise in the intraocular pressure. As the pressure increases the normally clear cornea at the front of the eye becomes waterlogged and hazy. The eye becomes painful and red. There may be "haloes" around lights and blurring of vision. Nausea and vomiting may also occur.

This form of glaucoma is more common in the long sighted who have smaller eyes and older people in whom the lens actually grows larger. In both cases the drainage canal in front of the iris closes off. This is known as angle closure glaucoma.

Chronic Glaucoma: By contrast, in this case, the blockage is gradual and there may or may not be a build up of pressure great enough to cause pain and discomfort. The intraocular pressure rises gradually and the eye adjusts partially to the raised pressure so the patient may not realise that there is a problem even though the optic nerve is being gradually damaged as the blood supply is being slowly cut off by the pressure. The effect on the vision is to cause blank areas to occur and enlarge until there remains only a small central island of vision. In chronic glaucoma the increase in pressure is not great enough to cause pain and discomfort and in this condition the drainage canal remains open but becomes silted up preventing drainage of the aqueous humour in front of the iris.

What are the tests

Regular eye examinations by an optician or ophthalmologist are the most important ways to detect glaucoma. The examination (which is quite painless) will comprise the following:

  • Measurement of the intraocular pressure (called tonometry)
  • Inspection of the drainage angle of the eye (called gonioscopy)
  • Evaluation of the optic nerve (called ophthalmoscopy)
  • Testing of the visual field of each eye

What is the treatment

Acute glaucoma: This is a medical emergency and the patient should be referred to hospital immediately. The aim will be to reduce the pressure as soon as possible and open the drainage channel for the eye fluid. A drug called Acetazolamide which prevents eye fluid being formed is given initially, as well as eye drops called pilocarpine to the affected eye which make the pupil smaller and open up the drainage canal.

If the pressure settles quickly then surgery or a laser can be used to drill a hole at the edge of the iris near the white of the eye to open up the drainage canal and so relieve the pressure.

Chronic glaucoma: Treatment is commonly by anti-glaucoma drops of various types and the aim here is to control the eyeball pressure gradually and help prevent further loss of vision. The eye specialist will prescribe beta blocking drugs (eg. Timoptol) which reduce production of fluid into the eye. They may be used alone or with pilocarpine drops or with adrenaline drop, both of which have effects on the production and drainage of fluid within the eye. Acetazolamide tablets may be used also.

A treatment called laser trabeculoplasty may work in some cases. This involves the creation of a drainage canal from within the eye to the exterior part just below the upper eyelid and so improve the drainage process.

Are there side effects of treatment

The eye drops have side effects. pilocarpine makes the pupil small and alters vision, whilst adrenaline can make the eyes sore and red. Beta blockers can worsen asthma-type breathing difficulties. Acetazolamide tablets may cause pins and needles in the hands and nausea.

Are there recommended lifestyle changes

practically speaking, the eye drops should be stored in a cool place and if opened will last about four weeks. Should hospital admission be necessary or a holiday planned, then it is important not to forget to continue using the eye drops

Where can I get more information

Apart from contacting your own Gp the following organisation may be of help:

International Glaucoma Association
Kings College Hospital
Denmark Hill
London
SE5 9RS
Telephone: 020 7737 3265

Sources

  • WARWICK, A, WRIGHT, B and CRICK, R. Glaucoma '95: a guide for patients, London, International Glaucoma Association
  • brUCKENHEIM, A.H. (1993) How does Glaucoma affect your ability to see Family Dr (CD Rom) Oregon, (USA) Tribune Media Services and Creative Multimedia
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