A patient with a spectacle Rx of -1.00 -2.00 x 160 has K readings of 42.50 @160 / 44.50 @ 70. What is the expected power of the contact lens needed if a rigid lens with a back surface radius of 7.94 is placed on the eye?

To determine the expected power of the contact lens needed in this scenario, we first need to analyze the parameters provided, which include the spectacle prescription, keratometry readings, and the back surface radius of the rigid contact lens.

The spectacle prescription indicates a -1.00 D sphere combined with a -2.00 D cylinder at 160 degrees. The keratometry readings reveal two principal meridians of corneal curvature: 42.50 D at 160 degrees and 44.50 D at 70 degrees. The average K reading or corneal power can also be calculated, but to simplify, we note that the K readings provide a reference for the power required to neutralize the eye's corneal shape.

When a rigid gas-permeable (RGP) contact lens is placed on the eye, it creates a new interface that alters the effective optical power due to the lens's design. The power of the contact lens can be estimated using the following formula:

[ P_{CL} = P_{sphere} + (K_{avg} - BCR) ]

Where:

• ( P_{CL} ) is the power of the contact lens.

• ( P_{sphere} ) is the spherical component of