Astigmatism
Astigmatism is a refraction error of the eye characterized by an aspherical cornea in which one axis of corneal steepness is greater than the perpendicular axis. Astigmatism causes difficulties in seeing fine detail, and can be often corrected by glasses with a cylindrical lens (i.e. a lens that has different radii of curvature in different planes) or by contact lenses or by refractive surgery. Astigmatism occurs when either the cornea or the lens of the eye is not perfectly spherical. As a result, the eye has different focal points in different planes. For example, the image may be clearly focused on the retina in the horizontal plane, but in front of the retina in the vertical plane.
Types of AstigmatismSimple*Simple hyperopic astigmatism*Simple myopic astigmatismCompound*Compound hyperopic astigmatism*Compound myopic astigmatismMixed astigmatism
External links Astigmatism MedlinePlus article AllAboutVision.com article Toric contact lenses – solution for people with astigmatism (article)
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