In the SRx example, which option shows the cylinder axis (x) value?

In the SRx example, which option shows the cylinder axis (x) value?

• A. 90 degrees
• B. 0 degrees
• C. 270 degrees
• D. 180 degrees

Answer: (D)

The cylinder axis is about the orientation of the cylindrical correction, measured in degrees from 0 to 180. In the SRx example, the axis is along the horizontal meridian, which is described as 180 degrees. Note that 0 degrees and 180 degrees describe the same horizontal orientation, while 90 degrees would be vertical, and 270 degrees isn’t used in standard axis notation. So the shown axis value is 180 degrees because it represents that horizontal orientation.

The cylinder axis is about the orientation of the cylindrical correction, measured in degrees from 0 to 180. In the SRx example, the axis is along the horizontal meridian, which is described as 180 degrees. Note that 0 degrees and 180 degrees describe the same horizontal orientation, while 90 degrees would be vertical, and 270 degrees isn’t used in standard axis notation. So the shown axis value is 180 degrees because it represents that horizontal orientation.