Flattening the GP base curve by 0.3 mm requires adding approximately how much power?

Flattening the GP base curve by 0.3 mm requires adding approximately how much power?

• A. +1.50 D
• B. -1.50 D
• C. +0.50 D
• D. -0.50 D

Answer: (A)

Flattening the back surface of a gas-permeable lens changes how much focusing power the lens contributes. Making the base curve flatter increases its radius, which reduces the lens’s converging effect. To maintain the same overall refractive correction, you compensate by adding power to the lens. The NBEO-style approximation is that a 0.3 mm flattening of the base curve requires about +1.50 diopters of added power. So the correct choice reflects this plus-power adjustment.

Flattening the back surface of a gas-permeable lens changes how much focusing power the lens contributes. Making the base curve flatter increases its radius, which reduces the lens’s converging effect. To maintain the same overall refractive correction, you compensate by adding power to the lens. The NBEO-style approximation is that a 0.3 mm flattening of the base curve requires about +1.50 diopters of added power. So the correct choice reflects this plus-power adjustment.