What is it?

Astigmatism occurs when the front part of the eye, the cornea, is not a regular symmetrical spherical shape. Instead, its shape is rather like that of the back of a spoon - longer in one direction than another. Because the cornea is an irregular shape, the eye can't focus light passing through it sharply on to the back of the eye or retina. So vision is blurred at all distances.

What causes it?

As the eye develops in the womb, several factors determine the shape of it, including inherited genetic factors and environment. It would seem that these factors can lead to an irregular curvature of the cornea, although the exact cause isn't known.

Who's affected?

Astigmatism is common and is usually present from birth. Most people have a slight astigmatism - it's rare for the cornea to have developed in a perfectly symmetrical way. But in mild cases, the eye can adjust to focus light adequately. In many cases of astigmatism the person also has other visual problems such as short-sightedness or long-sightedness. Two-thirds of people with short-sightedness also have significant astigmatism.

What are the symptoms?

In severe astigmatism, vision is blurred or distorted whether the person is reading close up or looking further into the distance. In milder cases the person may complain their vision is blurred at certain distances, that they've tired or dry eyes, that it's a struggle to focus or read, or that they've headaches, especially when trying to focus.

How is it diagnosed?

Astigmatism should be diagnosed by a qualified optometrist, ophthalmic surgeon or eye specialist. A full optometric examination should be done to assess the degree and extent of the problem. Small children, who may not be able to answer the optometrist's questions about what they can see, can be assessed using a test called retinoscopy that involves reflected light.

What's the treatment?

In most cases, astigmatism can be corrected by wearing properly fitted spectacles or contact lenses. Milder astigmatism may not need treatment unless the person is doing a job that puts intensive demands on the eyes, for example, computer work.