What base curve strategy would you use for a corneal power of 48 diopters?

What base curve strategy would you use for a corneal power of 48 diopters?

• A. Flatter base curve
• B. Steeper base curve
• C. Equal base curve
• D. No change

Answer: (B)

A corneal surface with high dioptric power is steeper, meaning it has a smaller radius of curvature. The base curve of a contact lens should match the corneal curvature to achieve proper alignment and stable fit. Using the approximation P ≈ (n − 1)/r for the cornea, with n about 1.3375, a 48 D cornea corresponds to r ≈ 0.3375/48 ≈ 0.0070 m, or about 7.0 mm. That radius is steeper than the average corneal radius (roughly 7.7–7.8 mm), so you’d select a base curve with a smaller radius (a steeper base curve) to fit well. A flatter or equal base curve wouldn’t match the curvature well, and no change would leave the lens poorly aligned.

A corneal surface with high dioptric power is steeper, meaning it has a smaller radius of curvature. The base curve of a contact lens should match the corneal curvature to achieve proper alignment and stable fit. Using the approximation P ≈ (n − 1)/r for the cornea, with n about 1.3375, a 48 D cornea corresponds to r ≈ 0.3375/48 ≈ 0.0070 m, or about 7.0 mm. That radius is steeper than the average corneal radius (roughly 7.7–7.8 mm), so you’d select a base curve with a smaller radius (a steeper base curve) to fit well. A flatter or equal base curve wouldn’t match the curvature well, and no change would leave the lens poorly aligned.