Astigmatism is an imperfection in the curvature of your cornea —
the clear, round dome covering the eye's iris and pupil — or in
the shape of the eye's lens. Normally, the cornea and lens are
smooth and curved equally in all directions, helping to focus
light rays sharply onto the retina at the back of your eye.
However, if your cornea or lens isn't smooth and evenly curved,
light rays aren't refracted properly. This is called a
refractive error. When the cornea has an irregular shape, it is
called corneal astigmatism. When the shape of the lens is
distorted, you have lenticular astigmatism. As a result of
either type of astigmatism, your vision for both near and far
objects appears blurry or distorted. It's almost like looking
into a fun house mirror in which you appear too tall, too wide
or too thin. People can be born with astigmatism — in fact, most
people probably are born with some degree of astigmatism — and
they may have it along with other refractive errors:
nearsightedness (myopia) or farsightedness