Astigmatism

A defect of the eye or of a lens, in consequence of which the rays derived from one point are not brought to a single focal point, thus causing imperfect images or indistinctness of vision.

(ophthalmology) impaired eyesight resulting usually from irregular conformation of the cornea; common in nearsighted people

(optics) defect in an optical system in which light rays from a single point fail to converge in a single focal point