Eyeglass frames have continually changed as fashions have transitioned through the decades, and eyeglass lenses also have also seen some improvements as well. Multifocal lenses have seen the most improvement though. These are the eyeglass lenses with multiple correction powers to help those 40 and older deal with the normal, age-related loss of near vision which is known as presbyopia.
History of multifocal eyeglass lenses
One of the many things that Benjamin Franklin, our early American statesman and inventor, gave us is the gift of the creation of the first multifocal eyeglass lenses. Before this invention anyone with presbyopia had to carry two pairs of eyeglasses, one for seeing distant objects and one for seeing up close.
Around the year 1780, Franklin in a stroke of pure genius (and necessity, I am sure) cut two lenses in half (one with a distance correction and one with a correction for near) and glued them together in the middle. This way the top half of the new lens then enabled the wearer to have distance vision and the bottom half helped them see things that are near.
This type of glasses lens, with a line going across the entire width of it, was first referred to as the Franklin bifocal and later on was given the name the Executive bifocal.
Modern multifocal lenses
Bifocals. Through the many changes that bifocals have seen since their inception, the vast majority of those changes have had to do with making these two-power lenses thinner, lighter and more attractive. Today in Fort Collins, Loveland and Greeley, we are seeing that the most popular bifocal for eyeglasses is called a flat-top (FT) or straight-top (ST) design. The part that contains the power for near vision is a D-shaped segment (or “seg”) in the lower half of the lens that is rotated 90 degrees so the flat part of the “D” faces upward.
FT or ST bifocals (sometimes also called a D-seg bifocals), are available in different-sized near segments. The most popular version sold in the United States has a near segment that is 28 millimeters wide, and is therefore called the ST-28 (or FT-28 or D-28) bifocal. This design offers a generous field of view for reading, yet keeps the near seg small enough to be cosmetically pleasing.
There are even more bifocal designs available in Northern Colorado. These include lenses with round near segments and bifocals where the near seg extends across the entire width of the lens (Executive bifocals).
All bifocals, however, have some limitations: although these lenses provide good vision for distance and near, they can sometimes leave the wearer’s intermediate vision (for distances at arm’s length) blurry and unclear.
This is where trifocals really shine. Trifocal eyeglass lenses have one morel ribbon-shaped lens segment immediately above the near seg for seeing objects in the intermediate zone of vision – approximately 18 to 24 inches away.
This intermediate segment provides you with 50% of the magnification of the near seg, making it the perfect vision option for computer usage, seeing your speedometer and other dashboard gauges when driving.
The option of trifocals is specifically popular among older presbyopes, people over the age 50 who do not possess the depth of focus than their younger presbyopes counterparts.
As with bifocals in Northern Colorado, the most popular trifocals have a flat-top (FT) design, with the near and intermediate segments being 28 mm wide. Trifocals with 35 mm wide segments are also wildly popular.
Limitations of bifocals and trifocals
There are a couple of drawbacks to bifocals and trifocals. One of these issues is the visibility of the lense transition. The transition in corrective powers is difficult for some people to adjust to and the visibility of the transition also speaks to the age of the wearer, this is also something that some people in Fort Collins, Loveland and Greeley have trouble adjusting to.
p>Several years past, the limits of ordinary bifocals and trifocals led to a profound breakthrough in multifocal eyeglass lens design: the progressive lens.
Progressive multifocal lenses
Here in Northern Colorado, progressive multifocal lenses (also called progressives, progressive addition lenses, and PALs) fulfill the real “multi-focal” lens name. With these lenses, instead of having just two or three powers, progressives gently graduate corrective powers from the top to the bottom of the lens. This gradual transition then offers a larger number of powers for clear vision at all distances.
Another added bonus to these lenses is that there aren’t any visible lines or abrupt changes of lens power in progressive lenses. The wearer then does not experience the “image jump,” so the wearer’s vision generally is more comfortable and seems more natural.
These advantages have caused progressive lenses to become the most popular multifocal lenses sold in the United States in recent years.
The right multifocal lenses for you
Choosing the right multifocal lenses for your vision correction needs will depend on your age, your visual needs, your budget and other factors. Visit us today for more information about bifocal, trifocal, and progressive lenses and to get a customized solution to your vision and eyewear needs.
For additional information or to schedule an appointment, please call 970-204-4020 or click on the link on the side of the page.