Generally for a soft contact lens you should start with the flatter base curve if the corneal power is less than how many diopters?

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

Answer: (B)

When fitting soft contact lenses, the base-curve choice is guided by how curved the cornea is. A flatter cornea corresponds to a lower corneal power, and in that case you start with a flatter base curve. The commonly used cutoff for this approach is about 45 diopters. If the cornea is flatter than 45 D, a flatter base curve helps the lens sit evenly, allows proper tear exchange, and keeps the lens from bearing too centrally or lifting at the edges. If the cornea is steeper (above 45 D), you’d begin with a steeper base curve to better match the surface and improve centration and comfort. The 45 D threshold is the standard guide, so corneas under that value warrant a flatter base curve, while higher powers require a steeper starting point.