What is Jackson's cross cylinder test is used for - and explain in detail?
Jackson's crosscylinder test : It is used to verify the strength and axis of the cylinder prescribed. The crosscylinder is a combination of two cylinders of equal strength but with opposite sign placed with their axes at right angles to each other and mounted in a handle . The commonly used crosscylinders are of +-0.25 D and +-0.5 D.  Verification of strength of the cylinder. Image: Jackson's cross cylinder Reference : A K KHURANA OPHTALMOLOGY,Edition 4,Page-555