In most astigmatic eyes, the oblong or oval shape causes light rays to focus on two points in the back of your eye, rather than on just one. This is because, like a football, an astigmatic cornea has a steeper, flatter curve.

In regular astigmatism, the meridians in which the two different curves lie are located 180 degrees apart. In irregular astigmatism, the two meridians may be located at something other than 180 degrees apart; or there are more than two meridians. Regular astigmatism is usually easy to correct, but irregular astigmatism can be complicated and more difficult to correct, depending on the extent of the irregularity and its cause.