Jackson Cross Cylinder
A Jackson cross cylinder (JCC) is a spherocylindrical lens with equal but opposite powers in the perpendicular principal meridians. The JCC is conveniently mounted with a handle oriented between the principal meridians in such a way that twirling the handle quickly exchanges the 2 meridians. (See the Quick-Start Guide.) Exercise 1-27 is an example of a JCC. A JCC may be of any power and always has the SE of zero. Thus, a JCC is any spherocylindrical lens with the SE of zero. We can fabricate such a lens by grinding a cylinder on 1 surface, paired with a sphere of half the power and opposite sign of the cylinder on the opposite surface.
Excerpted from BCSC 2020-2021 series : Section 3 - Clinical Optics. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.