Benjamin Franklin is generally credited with the invention of bifocals. He decided to saw his lenses in half so he could read the lips of speakers of French at court, the only way he could understand them.[1] Historians have produced some evidence to suggest that others may have come before 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.[2] Despite this, the College of Optometrists concluded:
Unless further evidence emerges all we can say for certain is that Franklin was one of the first people to wear split bifocals and this act of wearing them caused his name to be associated with the type from an early date. This no doubt contributed greatly to their popularisation. The evidence implies, however, that when he sought to order lenses of this type the London opticians were already familiar with them. Other members of Franklin's circle of British friends may have worn them even earlier, from the 1760s, but it is at best uncertain (and arguably improbable?) that split bifocal lenses had a famous gentleman inventor.[3]
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.
In 1955, Irving Rips of Younger Optics created the first seamless or "invisible" bifocal, a precursor to progressive lenses.[4] This followed Howard D. Beach's 1946 work in "blended lenses",[5][6] O'Conner's "Ultex" lens in 1910,[7] and Isaac Schnaitmann's single-piece bifocal lens in 1837.[8]
Construction
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 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 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.
Bifocals can cause headaches and even dizziness for some wearers. Adaptation 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 monofocal lenses for computer use.
Future
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 applied between two glass substrates.[citation needed]
Bifocals in the animal world
The aquatic larval stage of the diving beetleThermonectus marmoratus has, 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.[9]
^Letocha, Charles E. (November 1990). "The invention and early manufacture of bifocals". Survey of Ophthalmology. 35 (3): 226–35. doi:10.1016/0039-6257(90)90092-A. PMID 2274850.
^The College of Optometrists. . Archived from the original on 2011-06-13.
^"Hall of Fame Honors 12 Industry Veterans". Vision Monday. 12 November 2008.
^Clinical Optics, p. 276, by Troy E. Fannin and Theodore Grosvenor; published 2013 by Butterworth–Heinemann
^Encyclopedia of New York State, p. 123, by Peter Eisenstadt, published 2005 by Syracuse University Press
^Borish's Clinical Refraction, p 1109, by William J. Benjamin; published 2006 by Elsevier Health Publishing
^Borish's Clinical Refraction, p 1108 by William J. Benjamin; published 2006 by Elsevier Health Publishing
^Dawn Fuller (duly edited) (24 August 2010). "Bug With Bifocals Baffles Biologists". ScienceDaily. ScienceDaily LLC. from the original on 25 August 2010. Retrieved 25 August 2010. {{cite web}}: |author= has generic name (help)
Sources
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. Bibcode:2006PNAS..103.6100L. doi:10.1073/pnas.0600850103. PMC1458838. PMID 16597675.
External links
Franklin's letters to Whatley concerning double spectacles.
May 04, 2023
bifocals, bifocal, tensor, fundamental, matrix, computer, vision, eyeglasses, with, distinct, optical, powers, commonly, prescribed, people, with, presbyopia, also, require, correction, myopia, hyperopia, astigmatism, bifocal, lens, with, areas, differing, mag. For the bifocal tensor see Fundamental matrix computer vision Bifocals are eyeglasses with two distinct optical powers Bifocals are commonly prescribed to people with presbyopia who also require a correction for myopia hyperopia and or astigmatism A bifocal lens with areas of differing magnification Bifocals with separate lenses In this case the Swedish ethnologist Jan Ojvind Swahn Contents 1 History 1 1 Construction 2 Problems 3 Future 4 Bifocals in the animal world 5 See also 6 References 7 Sources 8 External linksHistory EditBenjamin Franklin is generally credited with the invention of bifocals He decided to saw his lenses in half so he could read the lips of speakers of French at court the only way he could understand them 1 Historians have produced some evidence to suggest that others may have come before 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 2 Despite this the College of Optometrists concluded Unless further evidence emerges all we can say for certain is that Franklin was one of the first people to wear split bifocals and this act of wearing them caused his name to be associated with the type from an early date This no doubt contributed greatly to their popularisation The evidence implies however that when he sought to order lenses of this type the London opticians were already familiar with them Other members of Franklin s circle of British friends may have worn them even earlier from the 1760s but it is at best uncertain and arguably improbable that split bifocal lenses had a famous gentleman inventor 3 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 John Isaac Hawkins the inventor of trifocal lenses coined the term bifocals in 1824 and credited Benjamin Franklin In 1955 Irving Rips of Younger Optics created the first seamless or invisible bifocal a precursor to progressive lenses 4 This followed Howard D Beach s 1946 work in blended lenses 5 6 O Conner s Ultex lens in 1910 7 and Isaac Schnaitmann s single piece bifocal lens in 1837 8 Construction Edit 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 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 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 Problems EditThis section does not cite any sources Please help improve this section by adding citations to reliable sources Unsourced material may be challenged and removed September 2022 Learn how and when to remove this template message Bifocals can cause headaches and even dizziness for some wearers Adaptation 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 monofocal lenses for computer use Future EditResearch 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 applied between two glass substrates citation needed Bifocals in the animal world EditThe aquatic larval stage of the diving beetle Thermonectus marmoratus has 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 9 See also EditBinocular vision Binocular rivalryReferences Edit Bronowski Jacob 1990 1973 The Ascent of Man London BBC Books p 271 ISBN 978 0 563 20900 3 Letocha Charles E November 1990 The invention and early manufacture of bifocals Survey of Ophthalmology 35 3 226 35 doi 10 1016 0039 6257 90 90092 A PMID 2274850 The College of Optometrists The Inventor of Bifocals Archived from the original on 2011 06 13 Hall of Fame Honors 12 Industry Veterans Vision Monday 12 November 2008 Clinical Optics p 276 by Troy E Fannin and Theodore Grosvenor published 2013 by Butterworth Heinemann Encyclopedia of New York State p 123 by Peter Eisenstadt published 2005 by Syracuse University Press Borish s Clinical Refraction p 1109 by William J Benjamin published 2006 by Elsevier Health Publishing Borish s Clinical Refraction p 1108 by William J Benjamin published 2006 by Elsevier Health Publishing 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 a href Template Cite web html title Template Cite web cite web a author has generic name help Sources EditG 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 Bibcode 2006PNAS 103 6100L doi 10 1073 pnas 0600850103 PMC 1458838 PMID 16597675 External links EditFranklin s letters to Whatley concerning double spectacles Retrieved from https en wikipedia org w index php title Bifocals amp oldid 1144644022, wikipedia, wiki, book, books, library,
