What is glaucoma?

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.

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.

Congenital glaucoma

It is very rare for children to be born with glaucoma but it is a recognised condition. There is 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

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 there is evidence of severe visual impairment.

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.

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.

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.

Other types of glaucoma

How does the doctor make a diagnosis?

If there is any suspicion of primary open angle glaucoma, the patient will usually be referred to an eye specialist (ophthalmologist).

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.

There are a number of different types of eye drops which are available to treat primary open angle glaucoma:

• carbonic anhydrase inhibitors
• Prostaglandin analogues
• Carbonic anhydrase inhibitors

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).

Laser treatment

Complications of such surgery include transient reduction in vision after the operation, but this usually recovers. Long-term effects of infection must always be considered.

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.

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 as treatment in the early stages may prevent visual loss. It is 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 examination.