If there is a decrease in the diopter (D) of base curve, the contact lens will be flatter/steeper.

If there is a decrease in the diopter (D) of base curve, the contact lens will be flatter/steeper.

• A. Flatter
• B. Steeper
• C. Unchanged
• D. Not predictable

Answer: (A)

Understanding how base curve diopter relates to curvature helps here. The diopter measure of the base curve is the inverse of the radius of curvature (D ≈ 1/R). So a higher diopter means a steeper curve (smaller radius), and a lower diopter means a flatter curve (larger radius). If the base curve diopter decreases, the radius increases and the lens becomes flatter. If it increased, the lens would be steeper; if there were no change, the curvature would stay the same; or if you didn’t consider this relationship, you might think the outcome is not predictable.

Understanding how base curve diopter relates to curvature helps here. The diopter measure of the base curve is the inverse of the radius of curvature (D ≈ 1/R). So a higher diopter means a steeper curve (smaller radius), and a lower diopter means a flatter curve (larger radius). If the base curve diopter decreases, the radius increases and the lens becomes flatter. If it increased, the lens would be steeper; if there were no change, the curvature would stay the same; or if you didn’t consider this relationship, you might think the outcome is not predictable.