23 May: Bifocals birthday

Bifocals Birthday Celebrates Ben Franklin's invention of the new glasses. In 1785 Benjamin Franklin wrote in a letter that he had invented bifocals, making it unnecessary to carry two pairs of glasses.

1. While Benjamin Franklin is often credited with the invention of bifocal glasses, Having written a letter on 23 May 1785 stating he was “happy in the invention of double spectacles”, so he’d not have to carry around two pairs of glasses, there is historical evidence to suggest that he may have got the idea from his friends in Britain, who’d been wearing them since the 1760s. Hence he would have been an early adopter of the technology rather than its inventor, and his words mean that he was pleased with the invention rather than that he was pleased with himself for inventing them.
2. Franklin may well be wearing bifocals in a painting of him by Stephen Elmer which dates to 1777.
3. The idea of split lenses had been suggested as early as 1683, though not necessarily for the same purpose as bifocals as we know them.
4. Early bifocal glasses were quite fragile because they were essentially two different lenses mounted together in a single frame.
5. In 1908, Dr. John L. Borsch Jr. patented a way of fusing the two different lenses together.
6. It was in 1955 that the “seamless” bifocal lens was invented by Irving Rips.
7. Trifocal lenses are a thing, too, with three different regions – distance, reading and intermediate (approximately arm’s length). These were invented by John Isaac Hawkins in 1827. They’re relatively rare nowadays as most people who need them opt for progressive lenses with a seamless gradient of focus.
8. They can take some getting used to. Wearers have to get used to a smaller field of view when reading or using a computer. Moving the eyes in order to read can cause headaches or dizziness in some people until they get used to moving their entire head or whatever they are reading, instead.
9. Since 2006, researchers have been working on glasses with lenses which can change their focus at the push of a button.
10. Bifocal lenses even occur in nature. The larvae of the diving beetle have two retinas, allowing them to switch their focus from distant to close up. This helps them catch their prey of Mosquito larvae.

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