1. A lens or optical system having different refractivity in different meridians.
2. A condition of unequal curvatures along the different meridians in one or more of the refractive surfaces (cornea, anterior or posterior surface of the lens) of the eye, in consequence of which the rays from a luminous point are not focused at a single point on the retina. Syn: astigmia.
Origin
[G. a- priv. + stigma (stig- mat-), a point]
astigmatism against the rule
compound hyperopic astigmatism
compound myopic astigmatism
corneal astigmatism
hyperopic astigmatism
irregular astigmatism
lenticular astigmatism
mixed astigmatism
myopic astigmatism
astigmatism of oblique pencils
regular astigmatism
simple hyperopic astigmatism
simple myopic astigmatism
astigmatism with the rule