Astigmatism results when the shape of the cornea (the clear section of the eye covering the iris) is not spherical; in other words, when the cornea is shaped more like the back of a dessert spoon rather than the back of a soup spoon. It may also exist, although less commonly, because of an irregular shaped lens within the eye.
Astigmatism is not a disease; it is merely a variation in the shape of the cornea or lens and is very common. It should be noted that in cases of continual progression of astigmatism, there is a need to exclude Keratoconus, which is a disease of the collagen fibres of the cornea, often genetic, that allows progression of a cone shaped cornea. This is best measured using a Corneal Topographer, which is available at Vision West, and treated using Rigid Gas Permeable Contact Lenses.
Moderate to large amounts of astigmatism will cause images to appear misshapen and blurry at any distance.
The usual way of correcting astigmatism is by wearing glasses or contact lenses. Most long sighted, short sighted and presbyopic people will also have small amounts of astigmatism which the optometrist will account for in a spectacle correction.
In children it is possible to measure a type of astigmatism that is actually secondary to focusing conditions, ie the eye shape may be correct but astigmatism is measured. This is best treated using behavioural optometry techniques including therapeutic spectacles and/or Vision Therapy.
There also exists lenticular astigmatism where the lens shape is irregular, again causing distortion of incident light.