Astigmatism

Astigmatism (from Gr. a, 'not;' stigma, 'a point'), a defective condition of the eye, in which rays proceeding to the eye from one point are not correctly brought to a focus at one point. In regular astigmatism (a congenital malformation), the curvature of the cornea is unequal in different meridians, those of greatest and least curvature being at right angles to each other. A spot of light is seen as a small oval, instead of a circle, as in a perfect eye; lines in one direction are seen clearly, while lines at right angles to these appear blurred. It can be remedied by the use of suitable glasses, whose surfaces are cylindrical, instead of being spherical like those of ordinary spectacles. Irregular astigmatism usually results from old injury or disease of the cornea, and can rarely be improved by glasses. See EYE.