Unequal curvature of the refractive surfaces of the eye. Thus a point source of light cannot be brought to a point focus on the retina but is spread over a more or less diffuse area. This results from the radius of curvature in one plane being longer or shorter than the radius at right angles to it. (DORLAND'S POCKET MEDICAL DICTIONARY,27th ed)
Astigmatism is a common eye disorder that occurs when the cornea or eye lens is curved incorrectly or wrongly shaped. When either of these malformations occurs, light is unable to focus properly on.the retina & the world becomes a blur
A condition in which the surface of the cornea is not spherical; causes a blurred image to be received at the retina. Unequal curvature of the lens of the eye creating a distorted image,and difficulty in seeing clearly that is caused by a change in the inner shape of the eye .