The bifocal lens, also called Franklin and split bifocal, was first invented by Benjamin Franklin in the 18th century. Multifocal lenses are commonly used to accommodate Presbyopia patients. The bifocal is the most basic multifocal lens. This lens consists of two prescriptions; usually a distance prescription with a reading addition placed in a lower segment. Since the basic split bifocal design, the bifocal has adapted many different lens designs to accommodate different preferences. Some include the Flat Tops, Round Segments, Executives, and the Blended Bifocal. Through the evolution of the bifocal there have been many styles added and discontinued. Below you will find several different types of bifocal lenses along with characteristics to accommodate different lifestyles and needs.
The flat top is also called the ”D” style multifocal lens. This design has a segment width that ranges from 25mm to 45mm. The Flat Top is regarded as one of the easiest multifocal lenses to adapt to, hence it is the most commonly used bifocal (FT 28mm is referred to as the standard size). This lens style is also one of the most readily available in almost any medium and including comfort lenses (ie. Polarized and Transition). The Flat Top utilizes the complete width of the segment giving the user a definitive reading and distance transition
This lens has been offered in widths ranges including 22, 25 and 28mm, however some sizes and mediums in this lens have been phased out and are no longer available. This lens gives the user a narrower initial reading range up top, because of its round top. We have used this lens on the few patients unable to tolerate a progressive multifocal. While it offers a much smaller reading area, it avoids the peripheral distortion found to some degree in all progressive multifocal lenses.
This lens is the closest to the original bifocal. It is often recommended as an occupational lens for patients involved with a lot of reading. This style segment offers the widest reading range of any of the bifocals for obvious reasons. Unfortunately, because of how the lens is ground, the executive style bifocal is considerably thicker and heavier than any other bifocal lens. For this reason, we tend to recommend a straight top lens design with a wider segment (35mm – 45mm) rather than the executive lens design.
The Blended bifocal is also called the Invisible Bifocal, Seamless, Blended 28 and the Younger. Irvin Rips is credited with inventing the first blended multifocal lens in 1955 creating a younger aesthetic look, which led him to launch Younger Optics. The segment width of the Blended bifocal is 28mm. This lens design attempts to improve cosmesis of the bifocal lens. Indeed, the lens shows virtually no sign of a segment. However, there is a 1 to 2mm blending range between the segment power and the lens prescription. This blending range has a distorted perspective that can prove to be non-adaptable for some patients. Newer progressive lenses are usually a better option for patients interested in an ” invisible” multifocal.