Jackson Cross Cylinder testing is primarily used to refine which component of a refraction?

• A. Cylinder power and axis
• B. Sphere and axis
• C. Prism effect
• D. Near add

Answer: (A)

Jackson Cross Cylinder testing targets astigmatic correction, refining the cylinder power and the axis. The cross-cylinder presents two perpendicular meridians with different powers, aligned with the anticipated astigmatic axes. By asking which orientation yields a sharper image and by adjusting the cylinder power and rotating the axis accordingly, you balance the two principal meridians. When both meridians are equally focused, you’ve achieved the correct cylinder power and axis. This step does not adjust sphere, prism effect, or near add.