Which pairing correctly matches base-curve modification with the required compensating power for GP lenses?

• A. Steepen BC → add plus power; Flatten BC → add minus power
• B. Steepen BC → add minus power; Flatten BC → add plus power
• C. Steepen BC → add zero power; Flatten BC → add plus power
• D. Steepen BC → add plus power; Flatten BC → add zero power

Answer: (B)

Base curve changes are the primary way we tune how a gas-permeable lens sits on the eye and how its optical power interacts with the cornea. When you steepen the base curve (make it more curved, smaller radius), the posterior surface sits closer to the cornea and the overall back-surface effect shifts toward more minus-like power. To keep the intended spectacle or refractive effect, you would add minus power to the lens. Conversely, flattening the base curve (making it less curved, larger radius) reduces that minus-like effect, so you compensate by adding plus power. This pattern—steepen BC with minus, flatten BC with plus—matches the correct pairing.