According to JND guidelines, which axis change is recommended when adjusting cylinder?

• A. 5 degrees or smaller
• B. 15 degrees or larger or exaggerated cylinder
• C. 25 degrees
• D. 45 degrees

Answer: (B)

Axis orientation adjustments are guided by perceptual thresholds. The eye generally needs about 15 degrees of cylinder axis rotation before the change in astigmatic correction becomes noticeable. So, when refining a cylindrical correction, making axis changes in 15-degree steps or larger ensures the patient can detect a difference and helps efficiently identify the best orientation. Smaller steps, like 5 degrees, are often below the Just Noticeable Difference and may not provide meaningful feedback. Larger jumps (25 or 45 degrees) aren’t standard incremental steps for routine refinement, though they might be used in broader testing; the practical guideline is to adjust by 15 degrees or more.