Generally you should start with the steeper base curve if the corneal power is greater than how many diopters?

Generally you should start with the steeper base curve if the corneal power is greater than how many diopters?

• A. > 40D
• B. > 45D
• C. > 50D
• D. > 35D

Answer: (B)

When selecting the base curve for a lens, the back surface curvature should match the corneal curvature. A higher corneal power means a steeper cornea (smaller radius of curvature), so starting with a steeper base curve helps the lens align properly, stay centered, and maintain a stable tear layer. Diopters and radius are inversely related, so the steeper cornea calls for a tighter back surface. The practical threshold used is corneal power greater than 45 diopters, which is why that value is the best starting point. Powers below that are typically fitted with a less steep base curve. Choices at 40D or 35D don’t meet the steeper-start criterion, while 50D is higher than the threshold and would still be guided by tolerance and fit during evaluation rather than the initial rule.

When selecting the base curve for a lens, the back surface curvature should match the corneal curvature. A higher corneal power means a steeper cornea (smaller radius of curvature), so starting with a steeper base curve helps the lens align properly, stay centered, and maintain a stable tear layer. Diopters and radius are inversely related, so the steeper cornea calls for a tighter back surface. The practical threshold used is corneal power greater than 45 diopters, which is why that value is the best starting point. Powers below that are typically fitted with a less steep base curve. Choices at 40D or 35D don’t meet the steeper-start criterion, while 50D is higher than the threshold and would still be guided by tolerance and fit during evaluation rather than the initial rule.