Glaucoma

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.
• 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.

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.

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.