How can one describe the lens shape of a spherical lens?

A spherical lens is characterized by having a uniform curvature that is consistent across its entire surface, which means that it has the same radius of curvature at every point. This property leads to a shape where all lines drawn from the center of the lens to the edge are equal in curvature. The term "single curvature" effectively encapsulates this feature, as it indicates that the lens surface curves uniformly in one direction, in contrast to other shapes like toroidal or aspheric lenses which have varying curvature.

In contrast, while the lens may be described as "flat," this does not adequately capture the essential nature of a spherical lens. Furthermore, "uniform" might suggest a lack of distinction in curvature but doesn't specify the defining characteristic of a singular curvature that defines spherical lenses. Lastly, "multi-focal" refers to lenses designed to correct for multiple vision conditions, such as presbyopia, which typically includes different zones for seeing at different distances. This is a distinctive characteristic that does not describe the fundamental shape of a spherical lens.