What is a characteristic of bifocal lens designs?

Bifocal lens designs are characterized by incorporating two distinct areas of vision correction, typically for distance and near vision, into a single lens. The correct choice mentions that bifocal lenses can be categorized as alternating/translating or concentric/aspheric.

Alternating/translating bifocals allow the wearer to look down at the reading portion of the lens, which is typically positioned at the bottom, while the upper section provides vision for distance. On the other hand, concentric/aspheric designs feature multiple power zones within a more blended or concentric layout, allowing for a smoother transition between different vision needs.

The other options do not accurately represent the full range of bifocal lens characteristics. Bifocal lenses indeed have more than one power change, and they can also be adapted for astigmatism. Furthermore, while prism stabilization methods can be used in some designs, they are not a strict requirement or characteristic of all bifocal lenses.