(ă-stig′mă-tizm )

[ ¹an- + Gr. stigma, stem stigmat-, point + -ism ]
ABBR: As A form of ametropia in which the refraction of a ray of light is spread over a diffuse area rather than sharply focused on the retina. It is due to differences in the curvature in various meridians of the cornea and lens of the eye. The exact cause is unknown. Some types show a familial pattern.
astigmatic (as″tig-mat′ik ), adj.
SYN: SEE: astigmia

against-the-rule astigmatism

Astigmatism in which the eye has greater refractive power in the horizontal than in the vertical meridian.

compound astigmatism

Astigmatism in which both horizontal and vertical curvatures are involved.

index astigmatism

Astigmatism resulting from inequalities in the refractive indices of different parts of the lens.

irregular astigmatism

Astigmatism in which the curvature of the cornea is asymmetrical.

mixed astigmatism

Astigmatism in which one meridian is myopic and the other hyperopic.

regular astigmatism

Astigmatism in which the abnormal curvature of the cornea is symmetrical with respect to an ocular axis.

simple astigmatism

Astigmatism along one meridian only.

with-the-rule astigmatism

Astigmatism in which the eye has more refractive power in the vertical meridian than in the horizontal meridian.