Cross cylinders is: (A) One plus cylinder and one minus cylinder of equal strength, (B) One plus cylinder and one minus cylinder of unequal strength, (C) Two plus cylinders, (D) Both minus cylinders
Answer is A. 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. Jackson's 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.