Astigmatism Abnormal curving of the cornea or lens of the eye The irregular curvature associated with astigmatism means that the optical system is not symmetric about the optical axis. Most commonly the cornea is affected such that the refractive power in one meridian is less than that of the perpendicular axis. Astigmatism of significant degree causes blurry vision. Astigmatism A type of refraction error associated with abnormal curvatures on the anterior and/or posterior surface of the cornea. UMLS:C0004106 SNOMEDCT_US:82649003 HP:0000483 Abnormality of refraction Abnormality of the curvature of the cornea