Because, like a football

Stigmatism occurs when the cornea is shaped more like an oblong football than a spherical baseball, which is the normal shape. 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 curve and a flatter one. Usually astigmatism is hereditary: many people are born with an oblong cornea, and the resulting vision problem may get worse over time. But astigmatism may also result from an eye injury that has caused scarring on the cornea, from certain types of eye surgery, or from videotoconus, excessive video viewing, causing a gradual thinning of the cornea.

A seemingly blurred view of the world; a short Renseiw astigmatic illustration, with singing. Enter here or on the cornea view above.