How to Refract in a Minus Cylinder?

Refracting with minus cylinder involves "chasing the red dots" using the Jackson Cross Cylinder (JCC) to refine cylinder power and axis.

Here's a breakdown of the process:

1. Determine Sphere Power: First, refine the spherical component of the refraction until the patient sees the clearest image possible without any cylinder correction.

2. Jackson Cross Cylinder (JCC) for Cylinder Axis:

   • Positioning: Present the JCC with its handle aligned with the current cylinder axis. The JCC has two axes: one with plus signs and one with minus signs. Two different presentations are given, by flipping the JCC.
   • Patient Feedback: Ask the patient: "In which position do you see the letters more clearly, Position 1 or Position 2?"
   • Axis Adjustment:
     • If the patient prefers the JCC position where the minus axis of the JCC is closer to the trial lens minus cylinder axis, adjust the trial lens axis in that direction. If they prefer the other position, adjust towards that direction. Typically, small adjustments (e.g., 5-10 degrees) are made initially.
     • Continue adjusting the axis until the patient reports no preference between the two JCC positions. This indicates that the cylinder axis is correctly aligned.

3. Jackson Cross Cylinder (JCC) for Cylinder Power:

   • Positioning: Present the JCC with its handle 45 degrees away from the cylinder axis. Again, flip the JCC to provide two choices.
   • Patient Feedback: Ask the patient: "In which position do you see the letters more clearly, Position 1 or Position 2?"
   • Power Adjustment: Use the mnemonics RAM (Red Add Minus) and WAP (White Add Plus).
     • If the patient prefers the position where the red axis of the JCC aligns with the minus cylinder axis of the trial lens, increase the minus cylinder power (add minus).
     • If the patient prefers the position where the white axis of the JCC aligns with the minus cylinder axis of the trial lens, decrease the minus cylinder power (add plus). Note that decreasing minus cylinder power is the same as adding plus cylinder power.
     • Adjust the cylinder power in 0.25 diopter steps.
     • Remember to adjust the sphere power by half of any cylinder power changes to maintain the circle of least confusion on the retina. For instance, for every -0.50D added to the cylinder, add +0.25D to the sphere.

4. Repeat: Iterate steps 2 and 3. After making adjustments to cylinder power, recheck the cylinder axis with the JCC, and then recheck the cylinder power. Repeat until no further improvement is found.

5. Final Sphere Refinement: Once the cylinder power and axis are optimized, re-refine the sphere power for best visual acuity.

Important Considerations:

• Patient Communication: Clear communication with the patient is crucial. Explain the process and what you're looking for in their responses.
• Small Steps: Make adjustments in small increments to avoid overcorrection.
• Fogging: Consider using fogging techniques to relax accommodation, especially in younger patients.
• Visual Acuity: Monitor the patient's visual acuity throughout the refraction to ensure improvement.