What would be the predicted contact lens power for a patient with Refraction: -2.00 -1.00 x 180, Ks: 43.50/44.50@090, BCR: 43.50?

• A. -2.50 D
• B. -2.00 D
• C. -1.50 D
• D. -2.25 D

Answer: (B)

When predicting the power for a gas-permeable spherical lens, use the sphere component of the refraction. The lens sits directly on the cornea, so there’s no vertex-distance adjustment like with spectacles, and the cylinder is not corrected by a spherical GP lens.

From the refraction, the sphere is -2.00 D and the cylinder is -1.00 D at 180. Since a spherical GP lens cannot correct astigmatism on its own, the power you would choose for a spherical GP lens matches the spherical component: -2.00 D. The other options would imply using the cylindrical component, applying a vertex-distance correction, or altering the power beyond the sphere value, which isn’t how spherical GP lens power is determined.