In a prescription context, the cylinder power is indicated by which component?

• A. Axis of astigmatism
• B. Sphere power
• C. Cylinder power
• D. Prism correction

Answer: (C)

Astigmatism is corrected with a cylinder lens, and the number that tells how strong that correction is comes from the cylinder power. This value measures the diopter strength needed to neutralize the difference in refractive power between the eye’s principal meridians. It’s paired with an axis that shows the orientation of that correction, but the axis itself does not indicate how strong the correction is. The sphere power covers the overall farsightedness or nearsightedness, not the cylindrical correction, and prism correction deals with shifting the image to align the eyes, not with correcting astigmatism. So the cylinder power is the part of the prescription that indicates how much cylindrical correction is required.