What is astigmatism?

I'm very short sighted, but over the years I've started to suffer from a astigmatism. I'd like to know what it is and what causes it.

15 October 2006

Part of the show Science of Sight, Eye Diseases and Animal Vision

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Question

I'm very short sighted, but over the years I've started to suffer from a astigmatism. I'd like to know what it is and what causes it.

Answer

The normal cornea, the bit at the front of the eye, is essentially spherical. But if it's not quite spherical, and is shaped like a rugby ball rather than a football, it creates a stigmatism. This means that the eye doesn't see perfectly in all planes. It's usually just the cornea that's shaped like a rugby ball, but it can sometimes be contributed to by the lens. This can run in families and there are certain diseases that cause it too.