Astigmatic

(as-tig-maf '-ik). Pertaining to or affected with astigmatism. •s Astigmatism. That condition of the eye wherein homocentric rays of light are not brought to a focus by the media. It is usually due to inequality of curvature of the different meridians of the cornea (corneal A.), but may be caused by imperfections of the lens (lenticular), unequal con- M I n ' Diagram Illustrating ths Formation of Astigmatic Images. The figures below give the images corresponding to the positions of the perpendicular lines above. The vertical rays are brought to a focus anterior to the horizontal. V. vertical rays; H. horizontal. traction of the ciliary muscle, or may perhaps be due to retinal imperfection. It may be acquired or congenital, and may complicate hypermetropia or myopia, producing either simple hypermetropic A., in which one principal meridian is emmetropic, the other hypermetropic or; compound hypermetropic A., in which both meridians are hypermetropic, but one more so than the other. Complicating myopia, we may in the same way have simple myopic or compound myopic A. In mixed A., one principal meridian is myopic, the other hypermetropic. Regular A. is when the two principal meridians are at right angles to each other. Irregular A., when different parts of a meridian have different refracting powers.