Astigmatism is a type of refractive error of the eye. Refractive errors cause blurred vision and are the most common reason why a person goes to see an eye professional.
Other types of refractive errors are:
People are able to see because the front part of the eye (cornea) is able to bend (refract) light and focus it onto the back surface of the eye, called the retina.
If the light rays are not clearly focused on the retina, the images you see may be blurry.
With astigmatism, the cornea is abnormally curved. This curve causes vision to be out of focus.
The cause of astigmatism is unknown. It is usually present from birth. Astigmatism often occurs together with nearsightedness or farsightedness. If astigmatism gets worse, it may be a sign of keratoconus.
Astigmatism is very common. It sometimes occurs after certain types of eye surgery, such as cataract surgery.