Astigmatism is an optical defect in which vision is blurred due to the inability of the optics of the eye to focus a point object into a sharp focused image on the retina. This may be due to an irregular or toric curvature of the cornea. The two types of astigmatism are regular and irregular. Irregular astigmatism is often caused by a corneal cone, and cannot be corrected by standard spectacle lenses. A 'toric' surface resembles a section of the surface of a Rugby ball or a doughnut where there are two regular radii, one smaller than the other one. This optical shape gives rise to astigmatism in the eye.

The refractive error of the astigmatic eye stems from a difference in degree of curvature refraction of the two different meridians (i.e. the eye has different focal points in different planes). For example, the image may be clearly focused on the retina in the horizontal plane, but not in the vertical plane. Astigmatism causes difficulties in seeing fine detail resulting in blurred vision. Three options exist for the treatment of astigmatism.

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