The lens or the cornea is an irregular shape, often described as a rugby ball shape, which results in the inability of the eye to focus a point object as a sharp image on the retina.
There are two types of astigmatism, regular and irregular.
Keratoconus is a condition of the cornea which causes central corneal thinning and changes in shape of the corneal surface (cone shaped cornea.) This causes a varied range of irregular astigmatism.
What you need to do
Regular astigmatism caused by the corneal or lens shape, can be corrected by toric spectacle or contact lenses. The spectacle corrective lenses have a toric surface which resembles that of a section of a rugby ball.
Irregular astigmatism is often caused by corneal scarring or irregularities in the crystalline lens. These cannot be corrected for using spectacles but there are surgical and contact lens options.