What is the typical diopter difference of the secondary curve of a RGP compared to the Central Power Curve (CPC)?

The typical diopter difference of the secondary curve of a rigid gas permeable (RGP) lens compared to the Central Power Curve (CPC) is indeed 1-2 diopters flatter. This design characteristic is essential for providing proper lens positioning and movement on the cornea.

When a secondary curve is created to be flatter than the central power curve, it helps to create a smooth transition in the lens' optical properties, allowing for better alignment with the corneal shape. A flatter secondary curve creates a wider area of tear film beneath the lens, facilitating adequate oxygen exchange, comfort, and reducing the risk of complications associated with RGP wear.

This design also aids in stabilizing the lens on the eye during blinks while maintaining the desired vision correction. Understanding the relationship between the CPC and the secondary curves is crucial for lens fitting and optimizing the performance of RGP lenses.