Which characteristic defines a round segment bifocal lens?

A round segment bifocal lens is characterized by having a circular near vision segment incorporated into the design. This circular segment is typically located at the bottom of the lens and allows for clear vision at close distances, while the upper portion of the lens provides distance vision. The design is specifically aimed at helping individuals with presbyopia, enabling them to transition between near and far vision smoothly. The circular shape of the near vision segment is what differentiates it from other bifocal designs, which may have rectangular or other shapes.

The other characteristics listed do not typically apply to round segment bifocal lenses. For example, a linear top section is more representative of other bifocal configurations. The optical center being at the edge is not accurate for this lens type, as the optical center is generally positioned directly in line with the wearer’s pupil for optimum vision. The application of color tint only at the edges refers to a feature seen in some sunglasses or specialty lenses, but it is not a defining trait of round segment bifocal lenses.