Astigmatism

Astigmatism is an out-of-roundness of one or more surfaces in the eye’s optical system.

An eye with no astigmatism is spherical in shape, like a marble. On the other hand an eye with astigmatism has a distorted shape, slightly like a grape.

In lesser degrees this can cause strain and discomfort after visual concentration; while in higher degrees astigmatism causes images at all distances to be distorted or blurred.