Jackson Cross-Cylinder: How to Refine Axis and Power

Last updated: October 2026

Short answer: the Jackson cross-cylinder (JCC) refines astigmatism in subjective refraction. Always refine the axis first, then the power. For axis, straddle the cylinder axis and rotate towards the preferred minus (red) position. For power, align with the axis and add or remove cylinder, adjusting the sphere to keep the spherical equivalent constant.

Before using the JCC

• Start with the best sphere (maximum plus for best vision).
• Show a line one or two lines above the patient's best acuity, or a round target, so the patient can compare clarity.
• Explain the question: "Which is clearer, one or two? It's fine if they look the same."
• On most phoropters, the red dots mark the minus cylinder axis of the cross-cylinder and the white dots mark the plus axis.

Step 1: Refine the axis

1. Position the JCC so that its handle is aligned with the cylinder axis (the red and white dots straddle the axis at 45°).
2. Flip the JCC and ask which position is clearer.
3. For a minus-cylinder phoropter, rotate the cylinder axis towards the red dot of the preferred position ("follow the red").
4. Use larger steps for low cylinders (for example, 10–15°) and smaller steps for high cylinders (about 5°).
5. Repeat until both positions look equally clear.

Step 2: Refine the power

1. Align the red dots, then the white dots, with the cylinder axis by flipping.
2. If the patient prefers red on axis, add −0.25 D cylinder. If they prefer white on axis, reduce the cylinder by 0.25 D.
3. Keep the spherical equivalent constant: for every −0.50 D of cylinder added, add +0.25 D to the sphere (and vice versa).
4. Stop when both positions look equally clear.

Checking for astigmatism not found on retinoscopy

If no cylinder was found, check at 90° and 180°, then at 45° and 135°. If the patient consistently prefers one position, add cylinder at that axis and refine as above.

Common mistakes

• Refining power before axis: the power will be wrong if the axis is wrong.
• Forgetting to adjust the sphere when cylinder power changes.
• Flipping too slowly; the patient should compare positions quickly.
• Not finishing with a final sphere check (and duochrome or binocular balance) at the end.

Frequently asked questions

Related: retinoscopy tips, duochrome test and vertex distance.