Main Entry: astig·ma·tism

Pronunciation: \ə-ˈstig-mə-ˌtiz-əm\

Function: noun

1 : 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
2 : a defect of vision due to astigmatism of the refractive system of the eye and especially to corneal irregularity—compare emmetropia, myopia