/euh stig"meuh tiz'euhm/ , n.
1. Also called astigmia /euh stig"mee euh/ . Ophthalm. a refractive error of the eye in which parallel rays of light from an external source do not converge on a single focal point on the retina.
2. Optics. an aberration of a lens or other optical system in which the image of a point is spread out along the axis of the system.
[ 1840-50; ASTIGMAT(IC) + -ISM ]