Abstract: An optical system utilizing a single spherical and two cylindrical lenses. The cylindrical lenses are located along the optical axis of the spherical lens and between the spherical lens aand an optical target. A first of the cylindrical lenses is fixed longitudinally but rotatable. The second cylindrical lens rotates with the first, but is relatively translatable along the optical axis. When the cylindrical lenses are nearly in contact, their net power is zero, and the patient views the target with the effect of the spherical lens' power only. The requisite spherical correction is determined by moving the target along a track that extends from a location well within the focal length of the spherical lens to a location well beyond it. Cylindrical correction is obtained by a combination of rotation and extension of the second cylindrical lens to produce variable negative cylindrical power and axis orientation.