Astigmatism astigmatism . Optics Astigmatism is an optical aberration in which a point object is imaged as two longitudinally separated and perpendicularly oriented line segments. The two generators of astigmatism are oblique ray incidence and surface toricity. Perfectly axisymmetric optical systems, like cameras and the like, are only affected by optical astigmatism.
Clincial astigmatism is a combination of both effects, anterior corneal toricity predominating.
Irregular astigmatism is not fully correctable with a spherocylindrical lens. Regular astigmatism is correctable with a spherocylindrical lens, because the axes of astigmatism are straight and mutually perpendicular. Regular astigmatism is typically quantified by the plus cylinder part of the patient's refractive correction . An corneal surface that induces regular surface astigmatism shows only slow variations of toric curvature and the principal directions of curvature.