cylindrical lens
a lens used to correct astigmatism, having one plane surface and one cylindrical, or one spherical surface and one toroidal. The meridian along the lens axis has no refractive power, but the meridian at right angles to the axis has maximum refractive power; thus the principal focus is a straight line, not a point. Symbol C. Abbreviated cyl. Called also astigmatic l.
Medical dictionary.
2011.