Origin: Greek suffix -ism
Astigmatism has 3 different meanings across 1 category:
(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
A defect of a lens such that light rays coming from a point do not meet at a focal point so that the image is blurred.