During FCC, if the patient reports that the vertical lines are darker, which lens power should be added?

During FCC, if the patient reports that the vertical lines are darker, which lens power should be added?

• A. Add Minus
• B. Add Plus
• C. No Change
• D. Add Neutral

Answer: (A)

In the fused cross cylinder test, you compare sharpness of two perpendicular meridians. The orientation where the lines look darker tells you which meridian is not yet adequately corrected. A minus lens adds negative power to the meridian perpendicular to the axis you choose, effectively reducing that meridian’s focusing power and moving its focal point back onto the retina. So if the vertical lines appear darker, you want to apply minus power to the vertical meridian (by orienting the cylinder so it affects that meridian) to bring both meridians into better focus. Adding plus would push the focal point forward and worsen the darker orientation, while no change would not correct the imbalance.

In the fused cross cylinder test, you compare sharpness of two perpendicular meridians. The orientation where the lines look darker tells you which meridian is not yet adequately corrected. A minus lens adds negative power to the meridian perpendicular to the axis you choose, effectively reducing that meridian’s focusing power and moving its focal point back onto the retina. So if the vertical lines appear darker, you want to apply minus power to the vertical meridian (by orienting the cylinder so it affects that meridian) to bring both meridians into better focus. Adding plus would push the focal point forward and worsen the darker orientation, while no change would not correct the imbalance.