Benjamin Franklin is generally credited with the invention of bifocals. Historians have produced some evidence to suggest that others may have preceded him in the invention; however, a correspondence between George Whatley and John Fenno, editor of The Gazette of the United States, suggested that Franklin had indeed invented bifocals, and perhaps 50 years earlier than had been originally thought. Since many inventions are developed independently by more than one person, it is possible that the invention of bifocals may have been such a case. Nonetheless, Benjamin Franklin is certainly among the first to wear bifocal lenses, and Franklin's letters of correspondence suggest that he invented them independently, regardless of whether he was the first to invent them.
In 1955, Irving Rips of Younger Optics created the first seamless or "invisible" bifocal, a precursor to all progressive lenses.
Original bifocals were designed with the most convex lenses (for close viewing) in the lower half of the frame and the least convex lenses on the upper. Up until the beginning of the 20th century two separate lenses were cut in half and combined together in the rim of the frame. The mounting of two half lenses into a single frame led to a number of early complications and rendered such spectacles quite fragile. A method for fusing the sections of the lenses together was developed by Louis de Wecker at the end of the 19th century and patented by Dr. John L. Borsch, Jr. in 1908. Today most bifocals are created by molding a reading segment into a primary lens and are available with the reading segments in a variety of shapes and sizes.The most popular is the D-segment, 28 mm wide. While the D-segment bifocal offers superior optics, an increasing number of people opt for progressive bifocal lenses.
20th Century Advances for stick on bi-focal lenses
There were various attempts at creating a bifocal lens that could adhere to the surface of sunglasses or safety glasses and in 1993 Peter Haye patented a D shaped lens that adhered through moistening the lens and creating a surface adhesion between the reading lens and the sunglass lens. the patent expired in December 2010.
Issues with this lens were the 'D' shape and the size - both inappropriate for modern day glasses - also the adhesion by water created air bubbles between the two lenses and also made them more likely to dry out and fall off.
Pete Haye died in 1999 and another company Neo Optix 20/20 acquired the license to use the patent but in 2012 they were apparently (as reported by a distributor at the Vision West Show September 2014) closed down by the FDA for manufacturing without medical device registration or iso 13485 - they re-emerged in late 2013 with a new name - HydroTrac - but with the same D shape and size and the same adhesion issue specifically the air bubbles between the lenses.
In 2014 a patent was filed by Malcolm McLean innovator and founder of 4Eyes - a company dedicated to resolving the issue of a stick on bi-focal reading lens with a new design that is both longer and narrower - to most emulate the movement of our eyes when reading 'Linear Tracking Motion' - that is horizontal from left to right.
Also the lower profile allows the user to look over the lens for distance viewing with 'catching' the top edge of the lens.
4Eyes uses an optically clear adhesive manufactured by 3M and adheres to the surface without bubbles even in high temperatures or humidity and can be re positioned for optimum vision by the user and is UV protected, non yellowing, chemical free and waterproof to 100m.
The new design fits all modern day style sunglasses and has a retail cost of $12.99 making them accessible to all consumers
Bifocals can cause headaches and even dizziness in some users. Acclimation to the small field of view offered by the reading segment of bifocals can take some time, as the user learns to move either the head or the reading material rather than the eyes. Computer monitors are generally placed directly in front of users and can lead to muscle fatigue due to the unusual straight and constant movement of the head. This trouble is mitigated by the use of trifocal lenses or by the use of monofocal lenses for computer users.
Linear Tracking Motion We read from left to right – and our eye movements are linear – horizontal – back and forth. If the reading element is badly positioned, the wrong size or bad shape our eyes ‘catch’ the edge of the bifocal lens and ‘disrupts’ focus and eye movement and ‘disorientates’ our vision and attention – very dangerous if driving.
In 2014 Malcolm McLean filed a patent for bifocal lenses are designed to have a wide field of vision that allows for the maximum possible side to side eye movement while keeping a low profile to see over the lens without any distraction. 4Eyes is self positionable so the user can determine the perfect position on their glasses.
In an interesting legal case reported in the UK in 1969, plaintiff's ability to use bifocals was impaired by accident.
Research continues in an attempt to eliminate the limited field of vision in current bifocals. New materials and technologies may provide a method which can selectively adjust the optical power of a lens. Researchers have constructed such a lens using a liquid crystal layer sandwiched between two glass substrates.
Bifocals in the animal world
The diving beetle Thermonectus marmoratus has recently become notable when it was discovered that its aquatic larval stage has been found to have used in its principal eyes two retinas and two distinct focal planes that are substantially separated, in the manner of bifocals to switch their vision from up-close to distance, for easy and efficient capture of their prey, mostly mosquito larvae. This is the first ever recorded use of bifocal technology in the animal world.
- The College of Optometrists. "The 'Inventor' of Bifocals?".
- Agarwal, R.K. (1984), Plaintiff's ability to use bifocals impaired by accident, The Ophthalmic Optician, 24 (25), page 898 (the title of this journal was changed to Optometry Today in 1985, published by the Association of Optometrists, London, England).
- Dawn Fuller (duly edited) (24 August 2010). "Bug With Bifocals Baffles Biologists". ScienceDaily. ScienceDaily LLC. Archived from the original on 25 August 2010. Retrieved 25 August 2010.
- Letocha, Charles E., M.D. (1990). "The Invention and Early Manufacture of Bifocals". Survey of Ophthalmology 35 (3): 226–235. doi:10.1016/0039-6257(90)90092-A. PMID 2274850.
- G. Li, et al. (April 2006). "Switchable electro-optic diffractive lens with high efficiency for ophthalmic applications". Proc. Natl. Acad. Sci. USA 103 (16): 6100–6104. doi:10.1073/pnas.0600850103. PMC 1458838. PMID 16597675.