When measuring a lens in minus cylinder, if the cylinder lines focus at a more plus reading than the sphere lines, rotate the axis wheel by how many degrees?

• A. 45
• B. 90
• C. 135
• D. 180

Answer: (B)

In minus cylinder lenses, the cylinder power is applied in the meridian 90 degrees away from the axis; the axis itself is the meridian with no cylinder power. If the cylinder lines focus at a more plus reading than the sphere lines, that tells you the cylinder effect isn’t aligned with the current axis orientation. To place the cylinder power into the correct meridian, rotate the axis wheel by 90 degrees. This swaps which meridian carries the cylinder power without changing the overall power in each meridian. Rotating 45 or 135 degrees would place cylinder power in a mixed orientation, and 180 degrees would just bring you back to the same orientation.