<prompt> Cross cylinders isOne plus cylinder and one minus cylinder of equal strengthOne plus cylinder and one minus cylinder of unequal strengthTwo plus cylindersBoth minus cylinders  <response>: A i.e. One plus cylinder and one minus cylinder of equal strength Cross cylinder is a combination of two cylinders of equal strength but with opposite sign placed with their axis at right angles to each otherQ and mounted in a handle. Jacksons cross cylinder test is used to verify the strength axis of the cylinder prescribed. The commonly used cross cylinders are of - 0.25 D and -0.5 D. 