Astigmatism

Astigmatism is a defect arising from unequal curvature of the eye's cornea or lens along different planes, so an astigmatic person cannot focus equally sharply on lines running in every direction at once -- generally a more serious defect than myopia or hypermetropia. It is corrected using specially-ground cylindrical lenses, whose curvature (and hence extra converging or diverging power) is added only along the specific plane that needs correcting, rather than …