Which component is critical in determining the meridians of a cylinder lens?

The axis is a critical component in determining the meridians of a cylinder lens because it precisely indicates the orientation of the cylindrical power within the lens. The axis is measured in degrees and helps in aligning the lens correctly in relation to the wearer's eye. A cylinder lens has two primary meridians: one with the maximum power and one with the minimum. The axis tells us where the maximum power meridian is located, ensuring that the lens is positioned in a way that effectively corrects for astigmatism.

In contrast, while curvature and power are also important characteristics of a lens, they do not directly define the orientation of the lens's cylindrical aspect. Curvature refers to the shape of the lens surface, and power indicates the degree of refractive strength the lens has; both are essential for understanding how a lens functions, but they do not specify the meridian orientations. The center of curvature relates to the specific point where the curvature is centered and is significant in lens manufacturing but not in defining the meridians of cylinder lenses. Thus, the axis is the correct and crucial component for determining the orientation needed to optimize correction for visual acuity.