In the initial trifocal Rx, what is the cylindrical power and axis in the distance portion?

In the initial trifocal Rx, what is the cylindrical power and axis in the distance portion?

• A. -0.50 x 120
• B. 0.00
• C. -1.00 x 120
• D. -0.25 x 60

Answer: (A)

The distance portion carries the same astigmatic correction as the overall prescription. In a trifocal, the add powers change for near and intermediate, but the cylindrical power and its axis stay the same across the distance, intermediate, and near portions unless a specific change is prescribed. Therefore, the distance portion uses the same cylinder and axis as the Rx. If the initial trifocal Rx has -0.50 diopters of cylinder at 120 degrees, the distance portion will be -0.50 x 120. A zero cylinder would imply no astigmatism correction, which isn’t the case here, and a different cylinder or axis would not match the prescribed Rx.

The distance portion carries the same astigmatic correction as the overall prescription. In a trifocal, the add powers change for near and intermediate, but the cylindrical power and its axis stay the same across the distance, intermediate, and near portions unless a specific change is prescribed. Therefore, the distance portion uses the same cylinder and axis as the Rx. If the initial trifocal Rx has -0.50 diopters of cylinder at 120 degrees, the distance portion will be -0.50 x 120. A zero cylinder would imply no astigmatism correction, which isn’t the case here, and a different cylinder or axis would not match the prescribed Rx.