Single Vision Lenses correct a single, particular vision such as distance if you’re nearsighted (a condition called myopia) or close up if you’re farsighted (a condition called hyperiopia). Multi-focal Lenses correct for two or more distances. There are three main types: bifocals, trifocals, and progressive additions lenses.
Bifocal Lenses have two vision zones separated with a visible line. The bottom segment provides correction for close up. The top part provides correction for distance vision
Trifocal Lenses have three vision zones separated with visible lines. The bottom segment provides correction for close up. The top part of the lens provides correction for distance vision. The middle section corrects for mid-range vision from about two to seven feet away.
Progressive Addition Lenses (also called “no-line bifocals” or “progressives” for short) correct vision for two or three different distances without visible segment lines seen in bifocal or trifocal lenses. Lenses offer a continuous, gradual change in prescription strength from the lower (reading correction) to the upper (distance correction) portion of the eyeglasses lens, providing correction for all distances. Progressive addition lenses are preferred to bifocals or trifocals because they provide the most natural correction and are the most attractive to wear- and because they avoid the “image jump” experienced in bifocals or trifocals when eyes move from one distance zone to another.