astig·ma·tism noun \ə-ˈstig-mə-ˌtiz-əm\
: a defect of an optical system (as a lens) causing rays from a point to fail to meet in a focal point resulting in a blurred and imperfect image
: a defect of vision due to astigmatism of the refractive system of the eye and especially to corneal irregularity—compare emmetropia, myopia
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