Astigmatism

It is possible to have difficulty seeing even if one is neither near nor far sighted, if the cornea of the eye is not perfectly curved. Airy devised eyeglasses to correct for that condition.
 George Biddell Airy England 1825 Astigmatism

It is possible to have difficulty seeing even if one is neither near nor far sighted, if the cornea of the eye is not perfectly curved. Airy devised eyeglasses to correct for that condition.