ASTIGMATISM

n. a visual disorder that occurs when the light rays of a visual stimulus do not all focus on a single point on the retina. Astigmatism is generally caused by uneven curvature of the cornea. As a result, light rays are refracted differentially, depending on the angle of the curve. The effect is an aberration or distortion of the visual image - not unlike the reflection seen in a deliberately distorted funhouse mirror. Astigmatism causes meridional amblyopia and can occur in the presence of myopia or hyperopia.