How does increasing the base curve radius affect the dioptric value of the base curve?

How does increasing the base curve radius affect the dioptric value of the base curve?

• A. Increase
• B. Remain the same
• C. Vary unpredictably
• D. Decrease

Answer: (D)

The back surface of a gas-permeable lens sets its base curve, and that curvature carries a dioptric value. A larger base curve radius means the posterior surface is flatter. Dioptric power for a curved surface is inversely related to its radius of curvature, so when the radius increases, the power contributed by that surface decreases. In practical terms, making the base curve flatter reduces the dioptric value of the base curve. This is why a steeper base curve (smaller radius) has a higher dioptric value, while a flatter base curve (larger radius) has a lower dioptric value. Note that the overall lens power also depends on other surfaces and the lens material, but for the base curve itself, increasing the radius lowers its dioptric value.

The back surface of a gas-permeable lens sets its base curve, and that curvature carries a dioptric value. A larger base curve radius means the posterior surface is flatter. Dioptric power for a curved surface is inversely related to its radius of curvature, so when the radius increases, the power contributed by that surface decreases. In practical terms, making the base curve flatter reduces the dioptric value of the base curve. This is why a steeper base curve (smaller radius) has a higher dioptric value, while a flatter base curve (larger radius) has a lower dioptric value. Note that the overall lens power also depends on other surfaces and the lens material, but for the base curve itself, increasing the radius lowers its dioptric value.