At Precision Family Eye Care, we know that the “Infamous B-word” is not something patients like to hear or talk about. But as our eyes naturally age and the lenses of our eyes start to falter (Presbyopia), the bifocal can be a tremendous improvement in comfort and ease over multiple pairs of glasses or always searching for those elusive reading glasses. In this section we will seek to demystify the Bifocal, how it works, what it’s like to wear one, the newest technology, and which type of bifocal lenses will work best for you.
Our recommendations on bifocal lenses are outlined at the end of this page.
Bifocal Lenses
Lined Bifocal Lenses (or just Bifocal)
Benjamin Franklin, one of our great nation’s founding fathers, has been widely credited for the invention of bifocal lenses. Although the term ‘Bifocal’ wouldn’t be coined until 18241, the first record of Franklin’s split lens design came from an English optician living in France in 1779 who, with difficulty, made a pair of bifocal lenses for Franklin based on his design.
The Lined Bifocal (figure above) works by having two sets of focusing areas. Through the top of the lens, a patient’s distance prescription allows clear distance viewing and the half-moon shaped bifocal allows clear viewing for near tasks. Although today’s Lined Bifocal comes in a variety of materials, coatings, and bifocal sizes and shapes, for a technology that is over two hundred years old it has remained very much unchanged.
While the Lined Bifocal is certainly a viable option, it has fallen out of favor due to the cosmetic appearance of the line, as well as one major flaw. When the eye doctor calculates a patient’s bifocal or reading power for glasses, the choice is made to allow clear vision for reading books and smaller print with a focusing point of around 16 inches from the glasses. With the ubiquity of computers, cell phones, and tablets, more and more of our visual tasks are taking place at intermediate distances at around arm’s length. This is outside of where the calculated bifocal power is most effective and results in a patient either using the top of the lens which can cause eye strain, fatigue and headaches or looking through the bifocal and leaning in toward the reading material which, at a minimum is inconvenient, but can also cause severe neck and back strain.
The Lined Trifocal Lenses (or just Trifocal)
The Lined Trifocal (figure above) was invented and patented by John Isaac Hawkins in 18272. This design of bifocal lenses piggybacked on Franklin’s invention and sought to solve the main problem associated with the Lined Bifocal – vision at arm’s distance. In addition to the distance and reading parts of the lens, as the name implies, the Lined Trifocal adds a third rectangular reading area just above the half-moon bifocal. This third area has roughly half of the bifocal’s reading power and thus focuses the vision further out for intermediate, arm’s distance tasks like computers or even reading the newspaper. While this solution does solve the Lined Bifocals main problem, the addition of a third lens area tends to make the lens a bit “busy” as your vision jumps between the different lens parts and lined appearance is still unpleasant for most patients from a cosmetic standpoint.
No Line Bifocal
The No-Line Bifocal Lenses
This bifocal lenses type goes by a whole host of different names such as Progressive Additional Lens (PALs), Blended Bifocal, Graduated Bifocal, Multifocal, among others. While confusing, all of these terms are synonymous and describe the exact same basic bifocal lenses design. The very first patent for this revolutionary type of bifocal lenses design was granted in 1907. However it was 50 years later (1953) that Bernard Maitenez received patent for the first modern day No-Line Bifocal while working for the Varilux company (still around today)3. Like many new technologies, it was very crude at first and not readily accepted by patients. Thankfully the forward thinking bifocal lenses companies persisted and innovated and the lineage of the No-Line Bifocal has resulted in some of the most amazing and technologically advanced lenses available today.
The basic design and how these lenses work is roughly the same. Unlike a lined Bifocal or Trifocal, a No-Line Bifocal blends the different reading areas into a seamless transition. A No-Line Bifocal wearer needs to simply tip or dip the chin to focus from distance vision to the car’s dashboard, to computer distance, all the way down to very fine print. This removes any of the empty areas typically noticed by Lined Bifocal and Trifocal wearers as they try to focus targets in between the different areas focused by the built-in specific reading areas.
While this seamless transition vision sounds great, the problems initially discovered by Bernard Maitenez in the 1950’s are still a problem for lens designer today. In order for lens makers to provide this transition from distance to near vision, No Line Bifocals “blend” the distance to the near prescription through special lens molds. Unfortunately, the blending process produces two large, blending zones on each side of the lower half of the No Line Bifocal lens that contain very higher and very irregular areas of prescription and distortion that make these areas nonfunctional for visual tasks (figure above). It is because of these unusable areas that the No Line Bifocal takes a period of one to two weeks for the brain to adapt and learn to uses the blended area and to avoid looking through the distorted “blending zones” sections. Lens manufactures have historically studied this adaptation process and found that 90-95% of individuals can adapt to this way of vision3. Even so, vast improvements have been made and the way in which No Line Bifocal lenses companies are working to lessen these distortion problems with today’s technology is simply amazing!
In today’s No Line Bifocal lenses market, manufacturers are putting computerized technology to work for you! In the past these lenses where formed with molds and all the prescription was ground only into the front surface which resulted in larger distortion zones, smaller reading and computer areas, and a much “harder” transition between the useable reading areas and the blended zones. Today’s most advanced No Line Bifocals lenses are called Digital or Free-Form No Line Bifocals. Their name comes from the manufacturing process that does not use a mold or form like typically No Line Bifocals lenses but is instead digitally surfaces each point on both sides of the lens with a tolerance of 0.001 of a Diopter (unit of prescription, like feet or inches). This technological leap decreases the blended area distortion by 20% and increases the reading and intermediate lens areas by 30%! This results no line bifocal lenses that are easier to adapt to and more comfortable to wear4. If you have had problems with No Line Bifocals in the past or simply want to take your computer and reading tasks to the next level, you owe it to your eyes to discover the newest advancement in bifocal lenses design.
Precision Family Eye Care Recommendations on Bifocals:
1. All bifocals lenses take time to adapt to and once your brain adapts to a certain type of bifocal, it is highly recommended that you remain with that style. Changing between a Lined Bifocal/Trifocal and a No Line Bifocal can be done, but it will take a substantial amount of adaptation time to achieve comfortable vision.
2. For all new bifocal wearers, we recommend trying a No Line Bifocal first. With all that is asked of our eyes in the technology advanced world we live in, the No Line Bifocal is far more useful and will provide better vision. Plain and simple.
3. If at all possible we recommend the newer Digital or Free-Form No Line Bifocals. Technology this good isn’t cheap, but after a few hours reading or a long day of computer use you WILL SEE AND FEEL the difference!
References
1. http://www.college-optometrists.org/en/college/museyeum/online_exhibitions/artgallery/bifocals.cf
2. http://en.wikipedia.org/wiki/Trifocal_lenses
3. http://en.wikipedia.org/wiki/Progressive_lens
4. http://www.allaboutvision.com/lenses/wavefront-lenses.htm