On a CL Rx, what component is used only when there is astigmatism correction, measured in degrees from 001 to 180?

The Axis is the correct component pertaining to a contact lens prescription when astigmatism correction is involved. It is measured in degrees from 001 to 180 and indicates the orientation of the cylindrical power needed to correct the astigmatism. The Axis specifies where the curvature should be placed to properly align with the patient's visual needs, ensuring that the lens addresses any irregularities in the cornea's shape that cause blurred vision.

Understanding the Axis is crucial, particularly for patients with astigmatism, as improper alignment can result in inadequate vision correction. The other components of a contact lens prescription serve different purposes: Sphere indicates the power needed for nearsightedness or farsightedness, the Base Curve refers to the curvature of the lens for fitting it to the eye, and ADD typically relates to additional power required for reading in multifocal lenses. Each serves a role, but only the Axis is specifically related to astigmatism and is vital for accurate lens placement for optimal vision correction.