In prescription notation, what does the number after the X signify?

In prescription notation, what does the number after the X signify?

• A. Axis of cylinder
• B. Sphere power
• C. Prism direction
• D. Pupil distance

Answer: (A)

The number after the X is the axis of the cylindrical correction. It’s an angle, given in degrees from 0 to 180, that shows the orientation of the astigmatism correction. The cylinder power corrects along a meridian that is perpendicular to this axis. For example, an axis of 180 means the cylinder’s power is applied along the vertical meridian (90 degrees away). This axis value is only present when there is astigmatism needing a cylindrical correction; the sphere power is read separately, and the axis does not indicate pupil distance or prism direction.

The number after the X is the axis of the cylindrical correction. It’s an angle, given in degrees from 0 to 180, that shows the orientation of the astigmatism correction. The cylinder power corrects along a meridian that is perpendicular to this axis. For example, an axis of 180 means the cylinder’s power is applied along the vertical meridian (90 degrees away). This axis value is only present when there is astigmatism needing a cylindrical correction; the sphere power is read separately, and the axis does not indicate pupil distance or prism direction.