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One pair of glasses for two distances
As he got older, Benjamin Franklin suffered from a condition that afflicts us all in the later years of life. From the age of 40 onwards, our eyes start to have difficulty focusing at close range, as their ability to accommodate, i.e. to focus at various distances, begins to decrease. It was only natural that a scientist of Franklin’s ilk should look for some way to remedy this situation.
In 1785, Benjamin Franklin presented a pair of what we now call bifocals in which two half-lenses were mounted on each side of an eyeglass frame. The upper lenses were used for distance, the lower lenses with a higher plus power for close-up vision. The term bifocal was coined by the mechanic John Isaac Hawkins, who proposed a design for trifocal eyeglasses in 1826.
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| Benjamin Franklins bifocal glasses |
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| operation of bifocal glasses | trifocal glasses |
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Progressive lenses
To permit comfortable vision at all distances, however, and also for cosmetic reasons, bifocal and trifocal glasses were constantly enhanced and refined to create multipurpose progressive lenses. Ongoing optimization of the surface design has considerably improved the physiological compatibility and wearing comfort of progressive lenses. And since modern office work and computer workstations make very special demands on our eyes, special-purpose progressives have now been designed to meet precisely these requirements. The result: progressive lenses have largely replaced bifocals and trifocals in the past few years. | |
| Benjamin Franklin Contributions: |
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