What is the true power of a CR-39 lens with a marked power of +4.00D front curve and -6.00D inside curve?

What is the true power of a CR-39 lens with a marked power of +4.00D front curve and -6.00D inside curve?

• A. -1.88D
• B. 0.00D
• C. 2.00D
• D. 4.00D

Answer: (A)

To determine the true power of a CR-39 lens marked with a front curve of +4.00D and an inside curve of -6.00D, you need to consider how the two curves interact to produce the overall lens power. The power of a lens is calculated using the formula for the combined power of two spherical surfaces: \[ P = P_1 + P_2 \] Where \( P_1 \) is the power of one surface and \( P_2 \) is the power of the other surface. The starting point is that each surface curve can be expressed in diopters based on its radius of curvature, with the power of a lens being positive for convex (plus) and negative for concave (minus) surfaces. In this case: - The front curve contributes +4.00D (a convex surface). - The inside curve contributes -6.00D (a concave surface). Therefore, we combine these values: \[ P = +4.00D + (-6.00D) \] \[ P = 4.00D - 6.00D \] \[ P = -2.00D \] This calculation results in a net power of -2.00

To determine the true power of a CR-39 lens marked with a front curve of +4.00D and an inside curve of -6.00D, you need to consider how the two curves interact to produce the overall lens power.

The power of a lens is calculated using the formula for the combined power of two spherical surfaces:

[ P = P_1 + P_2 ]

Where ( P_1 ) is the power of one surface and ( P_2 ) is the power of the other surface. The starting point is that each surface curve can be expressed in diopters based on its radius of curvature, with the power of a lens being positive for convex (plus) and negative for concave (minus) surfaces.

In this case:

• The front curve contributes +4.00D (a convex surface).

• The inside curve contributes -6.00D (a concave surface).

Therefore, we combine these values:

[ P = +4.00D + (-6.00D) ]

[ P = 4.00D - 6.00D ]

[ P = -2.00D ]

This calculation results in a net power of -2.00