How many diopters of "induced cylinder" would you expect from a back surface toric GP contact lens with the specified base curve radii?

When fitting a back surface toric GP (gas permeable) contact lens, the amount of induced cylinder can be calculated based on the difference in the base curves of the lens. The induced cylinder arises due to the difference in the optical power provided by the lens when it is placed on the eye compared to the power of the cornea.

In the case of a back surface toric GP lens, if the base curve radii of the lens are specified and there is a significant difference between the two curves, this introduces astigmatic power as well. The amount of induced cylinder can be estimated using the formula that correlates the difference in the base curves to the equivalent dioptric power.

In general, each 0.1 mm difference in base curve radius can induce approximately 0.50 D of cylinder. Therefore, when you know the specific base curves in question, the calculation can lead you to the total induced cylinder. For instance, if the difference between the two base curves is 0.9 mm, you would anticipate about 4.50 D of induced cylinder. This demonstrates how the design of the lens creates a spherical equivalent corresponding to the corneal profile and helps manage the astigmatism effectively.

The correct answer reflects