For FCC, if the vertical lines are sharper at the beginning of the test, do you add plus lenses or minus lenses until both the vertically and horizontally oriented lines are equally sharp?

For FCC, if the vertical lines are sharper at the beginning of the test, do you add plus lenses or minus lenses until both the vertically and horizontally oriented lines are equally sharp?

• A. Plus lenses
• B. Minus lenses
• C. No change
• D. Flip orientation

Answer: (B)

Balancing focus between the two principal meridians is what this test is about. When the vertical lines look sharper at the start, the vertical meridian is closer to focus than the horizontal one. To bring the two into equality, you introduce defocus by subtracting power—that is, you add minus lenses. The minus lenses push the overall focusing more myopically, which tends to blur the sharper meridian enough to match the other, giving a point where both orientations are equally sharp. Using plus lenses would push the focus in the opposite direction and typically widen the gap rather than close it, while no change leaves the difference unresolved and flipping orientation doesn’t address the balance.

Balancing focus between the two principal meridians is what this test is about. When the vertical lines look sharper at the start, the vertical meridian is closer to focus than the horizontal one. To bring the two into equality, you introduce defocus by subtracting power—that is, you add minus lenses. The minus lenses push the overall focusing more myopically, which tends to blur the sharper meridian enough to match the other, giving a point where both orientations are equally sharp. Using plus lenses would push the focus in the opposite direction and typically widen the gap rather than close it, while no change leaves the difference unresolved and flipping orientation doesn’t address the balance.