People with astigmatism have an unevenly curved cornea (the clear covering at the front of the eye) or an unevenly curved lens inside their eye, shaped more like a rugby ball than a football. Imagine a rugby ball sliced in half, lengthways.

The cut surface is an oval shape, and imagine you are looking at it from its pointed end - the sides curve up steeply. Now imagine you're looking at it from halfway between the two pointed ends - the sides curve much less steeply. This is an exaggerated version of the shape of an astigmatic cornea.

It is corrected by spectacles with a cylinder shape built into the lenses at a certain angle. Contact lenses can also correct astigmatism - mild astigmatism can be corrected by an ordinary gas-permeable lens. Those who prefer a soft lens or have higher amounts of astigmatism can use specially designed, 'toric' soft lenses.