Bifocal and progressive lenses are both multifocal lenses that allow you to see in the distance through the top of the lens and see up close through the bottom of the lens.A bifocal lens has two areas of vision correction, one in the top for distance and one in the bottom for close work, usually up to about 20 inches.
Bifocals usually have a distinct line defining the reading portion of the lens. The most common type of bifocal, called a D-segment, has what looks like an upside-down half moon in the bottom of the lens.
Like bifocal lenses, progressive lenses (also called ""invisible bifocals"") also allow you to see in the distance through the top of the lens. Progressive lenses have an area in the middle and lower part, however, that lets you see objects up to 36 inches away.
Progressive lenses do not have visible lines, but if you look closely, you can see a small mountain-shaped area in the bottom of the lens. Source:
