As their name suggests, bifocal eyeglass lenses have two lens powers — one for distance and one for near.

Flat-top or D segment bifocal eyeglass lens
Flat-top bifocal lens (also called a D-seg or straight-top).

Round segment bifocal lens
Round seg bifocal lens.

Franklin or executive bifocal lens
Executive bifocal lens (also called the Franklin bifocal).

The lower half of a bifocal lens contains the near segment for reading and other close-up tasks. The rest of the lens in all our glasses and sunglasses has no correction at all in it, perfect if you have good distance vision, and you can wear them over the top of contacts as well.