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Bifocal and Trifocal Lenses

ben franklin

Ben Franklin invented the "Executive" bifocal.

For years, many individuals the world over have been wearing bifocals and trifocals. This is due to normal age related vision loss, called presbyopia. As we age, the eye has less ability to focus on subjects nearby. Nothing to worry about, as it eventually happens to almost all of us.

Bifocal and trifocal lenses can aid in the restoration of near vision. Unfortunately, due to the complex nature of trifocal lenses, Visio-Rx is unable to offer these.

History of Trifocals and Bifocals

The person who was known to have made the very first multifocal lens was Benjamin Franklin. He was not just a wise American statesman, but he was also a great inventor. Before he invented such an ingenious creation, individuals with presbyopia had to bring with them 2 eyeglass pairs – one for looking objects up close and the other for focusing on distant objects.

During the 1780’s Franklin decided to cut 2 lenses into two (one half for near vision and the other half for distance correction. These were the very first bifocal lenses ever made. It had a line dividing its entire width which acts as a separator for the near and distance correction lenses. It was primarily known as the Franklin bifocal and today is known as the "Executive" bifocal. As time passed by, Franklin’s bifocals were gradually refined, but still have the defining line in the lens, separating near and distance vision.

Video: Bifocals explained.

Trifocal lenses are more or less like bifocals, but have a 3rd smaller lens segment that is used for intermediate vision. This segment is placed directly over the near segment, thus bringing you a total of 3 power zones. Again, these lenses have lines clearly separating the distance, intermediate and near vision zones.

Options for Bifocal Lenses

At Visio-Rx, we offer a wide variety of bifocals. We offer bifocals with round, D shaped or or invisible round near vision segments. For more information, please see the table below.

Bifocal information table chart
click to enlarge table.

Bifocals may be good for tasks such as reading or driving; however, these lenses are unfortunately limited in terms of their capacity to bring clear vision at in between points like computer monitor distance.

Bifocals for use at desk or computer

It is possible to order bifocal glasses specifically for use at a desk or with a computer. In that case, the top portion of the lens will be have the exact power to see clearly at your preferred working distance (for a computer: the distance between your eyes and the screen). This provides a nice large viewing area for the screen (as opposed to a narrow slot in case of trifocals), which reduces tired eyes. Please note that such lenses are not intended for general use, as they do not provide distance vision. 

bifocal lens

Bifocals have a clear line that separates the near vision segment from distance vison.

Image jump

An unpleasant phenomena in certain bifocal glasses is the "image jump". This means that when the eye transitions from the far zone to the near zone, the angle under which an object is viewed suddenly changes.

Safety Notes

Even though bifocals offer a wider vision range than single vision lenses in glasses, there is a downside: these lenses can make things around your feet hazy unless a wearer tilts his or her head down. This is a big safety issue, especially when wearers walk down the stairs or step off of sidewalk curbs. Always use caution when performing these tasks.

Progressives

Progressive lenses are multifocal lenses that combine corrections from near to distance vision into a single lens without any visible separation line or image jump.

A progressive lens is superior in almost all respects compared to the bi-focal and tri-focal lenses. Hence it is no surprise that sales of the bi and trifocal lenses have shown a significant decline in the past 15 years, a trend that is not expected to reverse itself.

Video: Back surfacing and front surfacing of freeform progressives explained.

Nowadays, most people prefer using progressive lenses over trifocals and bifocals because of the improved vision characteristics and the more youthful appearance experiences, as there are no lines separating the vision zones.

Changing to a Progressive Lens

Most people will be able to successfully transition from bi or trifocals to a progressive lens. Especially the modern progressive lens designs (back side freeform) have made the change-over easier than it was in the past. A change-over will take a bit more time than for first time users (previous single vision users), but most bi/trifocal users will make the transition. However, some people over the years have grown so accustomed to their bifocals or trifocals that an upgrade to progressives becomes rather uncomfortable. In view of the benefits of a progressive lens, it is worth a try. And with the low prices at Visio-rx.com for these superior progressive lenses, it will not break the bank. VRXend

 
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