There is no single known cause for astigmatism, though several scientists and research circles have cited genetics as a big factor. If one’s family lineage has a history of vision-blurring astigmatism, the children are more likely to follow suit. However, it can also be caused by untoward incidents, like an injury to the eye or a complication following a surgery. In some cases, though, diseases like diabetes have been linked to astigmatism—high blood sugar levels have been known to cause shape changes in the lens.
Virtually anyone can develop some degree of astigmatism, as a lot of people have slight variations in the shapes of their corneas or lenses which may or may not lead to impaired vision. The cornea is supposed to be smooth and rounded for clear, 20/20 vision (it starkly resembles the surface of a Ping-Pong ball cut in half). However, people with astigmatism have corneas whose surfaces are more curved (reminiscent of the top of a football).