What causes astigmatism?

Astigmatism is a common and usually minor condition of the eye that causes blurred or distorted vision. It occurs when the cornea or lens is not a perfectly curved shape. Most people who wear glasses have astigmatism.

If left untreated, astigmatism can also cause: headaches and eye strain and fatigue (tiredness) – particularly after doing tasks that involve focusing on something for a long period of time, such as reading or using a computer.

Astigmatism is usually present at birth. It can run in families and seems to be more common in premature or low birth weight babies, perhaps because the cornea does not have enough time to develop properly.

Other possible causes of astigmatism include:

(1) injuries to the cornea, such as an infection that scars the cornea
(2) changes to the cornea caused by eye surgery
(3) keratoconus and keratoglobus – eye conditions that cause the cornea to bulge, get thinner and change shape
(4) some conditions that affect the eyelids
(5) other diseases that affect the cornea or lens

For most people, this is a very mild, minor problem which may not even be noticed. However, with more advanced astigmatism, there can be a variety of symptoms including blurred vision, light sensitivity (photophobia), eye strain and fatigue (especially after long periods of concentration, such as when using a computer), and headaches.

You may have difficulty seeing one colour against another (contrast) or you may experience distorted images, such as lines which lean to one side. Severe astigmatism can cause double vision.

Astigmatism in only one eye may cause lazy eye (amblyopia) if present from birth. The affected eye does not learn how to see because the brain ignores the signals it receives. Amblyopia can be treated with eye patching if diagnosed early enough, before the vision pathways in the brain are fully developed.

In many cases the symptoms of astigmatism are so mild that no treatment is needed. If vision is more significantly affected, glasses, contact lenses or surgery can correct the vision....