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Bifocals Benjamin Franklin
Bifocals are glasses with two optical powers, commonly prescribed for individuals with presbyopia who also require correction for myopia, hyperopia, and/or astigmatism.
History
Benjamin Franklin is often credited with the invention of bifocals, which he used to read French speakers’ lips at court. While some historians suggest others may have come before him, correspondence between George Whatley and John Fenno suggests that Franklin invented bifocals 50 years earlier than initially thought.
The College of Optometrists concluded that Franklin was one of the first people to wear split bifocals, which caused his name to be associated with the type from an early date. This contributed to the popularization of split bifocal lenses. However, evidence suggests that London opticians were already familiar with them when Franklin sought to order these lenses.
Other members of Franklin’s circle of British friends may have worn them even earlier, from the 1760s.
The invention of bifocals may have been independently developed by multiple individuals, as many inventions are independently developed. John Isaac Hawkins, the inventor of trifocal lenses, coined the term in 1824 and credited Benjamin Franklin.
Irving Rips created the first seamless bifocal in 1955, followed by Howard D. Beach’s work in 1946, O’Conner’s Ultex lens in 1910, and Isaac Schnaitmann’s single-piece bifocal lens in 1837.
manufacture
Original bifocals were designed with convex lenses in the lower half of the frame for close viewing, and the least convex lenses on the upper. However, by the early 20th century, two separate lenses were combined in the rim of the frame, leading to early complications and making spectacles fragile.
Louis de Wecker developed a method for fusing lens sections together, which was patented by John L. Borsch Jr. in 1908. Today, most bifocals are created by molding a reading segment into a primary lens, available in various shapes and sizes.
hereafter
Researchers are working on a lens that can selectively adjust the optical power of a bifocal, using a liquid crystal layer applied between two glass substrates, to eliminate the limited field of vision in current bifocals.
issue
Bifocals can cause headaches and dizziness in some users, and adjusting to the small field of view can be time-consuming. Computer monitors placed directly in front of users can lead to muscle fatigue due to constant head movement. Monofocal lenses can help mitigate this issue by providing a clearer view
Bifocals in the animal world
Thermonectus marmoratus, a diving beetle, has two retinas and two distinct focal planes in its primary eyes, allowing it to switch vision from close to distance, primarily for capturing mosquito larvae, effectively.
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