How do eyeglasses work?

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According to the Vision Council of America, 75% of adult Americans wear glasses, contacts, or both. If you wear eyeglasses you know you wouldn’t be able to function in your day to day life without them. But have you ever wondered how those things of the bridge of your nose actually work? And when did people even start wearing them?

History

The history of eyeglasses dates back to the late 13th century in Pisa, Italy. The specific inventor is still unknown but it is known that by 1301 there were regulations governing the sales of eyeglasses in Venice. By the 1400s, Florence became a leader in the production of eyeglasses. In the 15th century, the demand for eyeglasses increased greatly after the invention of the printing press.

It is well-known that American founding father Benjamin Franklin invented bifocals. Franklin suffered from a condition known as presbyopia, which is related to aging eyes and results in progressively worsening ability to focus clearly on close objects. Bifocals are eyeglasses with an upper and lower half, the upper for distance, and the lower for reading. By the 20th century, eyeglasses the emphasis shifted away from purely a functional matter and toward style. Glasses are now seen as fashionable and even people who don’t need glasses often wear them as an accessory.

How do they work?

To know how eyeglasses work, we should first understand how our eyes work. At the back of your eye is the retina, a layer of cells that react to light. The reaction from the retina is sent to the brain and the brain translates this reaction into an image, which is what you see. When you look at something, light rays focus inside your eye. These rays focus directly on the retina in someone with perfect vision. For most people, these rays do not focus directly which results in irregularities. Lenses, which are bent pieces of glass, are designed to correct these irregularities by bending light rays as they approach your eye and focusing them directly onto your retina.

Today

The most common use of glasses is for people who are nearsighted and farsighted. For nearsighted people, distant objects are out of focus. This is corrected by using a convex lens, which bends light toward the bottom and top of the lens to push the focal point to the retina. For farsighted people, close objects are out of focus. A concave lens is used to spread light from the center of the lens. The strength of the lens or prescription is measured diopters. The strength of the lens controls how much light is bent.

Perfect vision is an extreme rarity, however, most people can now see clearly thanks to the invention of eyeglasses. Who knew how much of an impact two bent pieces of glass could have on millions of people around the world.

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