What characterizes an aspheric lens design?

An aspheric lens design is characterized by a gradual power change from the center to the edge. This design allows for a more complex curvature than traditional spherical lenses, leading to a reduction in aberrations and an improvement in visual clarity, particularly at the edges of the lens.

Unlike spherical lenses that have a uniform curvature and thus a constant power throughout, aspheric lenses are shaped in a way that their power gradually increases or decreases. This gradual transition helps to provide clearer peripheral vision and reduces distortion, making them particularly beneficial for correcting vision in higher prescriptions or for certain conditions like presbyopia.

In contrast, the other options describe lens characteristics that do not apply to aspheric designs. A sudden change in lens power creates abrupt visual shifts, which can be disorienting and are typically found in other types of lenses, but not aspheric ones. Concentric rings of power refer to a specific design seen in multifocal lenses, where power varies in distinct zones rather than continuously. A fixed power across the lens would describe a typical spherical lens, where the power remains constant throughout. Thus, the defining trait of a gradual power change encapsulates the advantages and functionality of aspheric lens designs.