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If you’re reading this sentence, there’s a good chance you’re using corrective lenses like glasses or contacts. After all, Statista reports that over 60% of U.S. adults wear prescription eyeglasses. For many people, glasses or contacts are essential to engaging in the activities of daily life, such as recognizing faces and objects, reading, driving and navigating screens. While modern lifestyles have contributed to the need for glasses earlier in life — as explained in the journal Nature — there’s a long history of human eyesight deteriorating with age.

The Roman orator Cicero (106-43 BC) lamented that he needed his slaves to read texts to him aloud. Just a generation later, the Roman philosopher Seneca (4 BC to 65 AD) is said to have used a glass globe of water to assist with reading. Early corrective lenses were not glasses to be worn on the face, but similar to magnifying glasses that could be held over objects of interest.

This Roman knowledge of magnification would be lost among Europeans during the medieval period, and it might have been lost entirely if not for the work of Arab scholars, as The American Biology Teacher notes.

Corrective lenses work by altering the direction of incoming light waves so that an image is focused when it hits the retina at the back of the eye.

Common vision problems include nearsightedness, farsightedness and presbyopia. Nearsightedness is when nearby objects appear clear, but faraway objects appear blurry. This occurs when the eyeball is too long, which leads to light waves focusing in front of the retina. Farsightedness is when faraway objects appear clear, but nearby objects appear blurry. This can occur when the eyeball is too short, so the focal point of light is behind the retina. Farsightedness can also be caused by presbyopia, which is when the lens near the front of the eye loses elasticity and cannot adjust to adequately focus on nearby objects. Presbyopia often develops in middle age.

Around 1000 AD, Italian monks developed and used polished domes of transparent quartz as reading stones. These could magnify text and correct for farsightedness, as explained in the journal Survey of Ophthalmology.

An unknown Italian inventor developed corrective lenses for glasses around 1285 AD. Glass-blown lenses were secured into frames made of wood, leather or animal horn. The glasses were then held in front of the face with one hand or clipped onto the nose. A painting from 1352 depicting monks reading and writing manuscripts shows one using a magnifying glass while another wears glasses, according to Survey of Ophthalmology. At that time, monks were some of the only people who learned to read and write. Around 1440, the invention of the printing press made reading more accessible and increased the demand for glasses.

In the 1600s, Spanish craftsmen added ribbon so that glasses could be looped over the ears. Other noteworthy styles included the monocle (for one eye only), the lorgnette (which was held in front of the eyes with a long handle) and scissor-glasses (which could be folded). In 1730, English optician Edward Scarlette added rigid temples that extended over the ears, which is the most common style today. In 1784, Benjamin Franklin invented bifocals by cutting and joining together convex and concave lenses, which allowed him to see near and far without switching glasses.

Contact lenses are thin corrective lenses worn “in contact” with the eye. They work in essentially the same way as glasses, according to All About Vision: by refracting incoming light so that an image is focused when it hits the retina. For people who are nearsighted, the lenses are thicker on the outer edges and thinner in the middle, just like concave lenses for glasses. For farsightedness, the thickest part of the lens is in the middle, just like convex lenses for glasses. Contacts can be much thinner than eyeglass lenses because they rest directly on the eye.

“Who invented corrective lenses” is a complex question to answer. Like many scientific discoveries, there were many important steps toward creating the first contact lens. Leonardo da Vinci is given credit for the concept of contact lenses, as described by Lenstore. His sketches from 1508 show a person placing their face in a curved glass bowl filled with water to see objects on the other side more clearly. The water would be in contact with the eyes, so technically it’s a contact lens. In 1636, after reviewing da Vinci’s work, Frenchman René Descartes proposed placing a glass tube filled with liquid in direct contact with the cornea to correct vision. In 1801, English scientist Thomas Young used Descartes’ idea to create a 1/4-inch-long, water-filled glass tube that he secured to his own eye with wax. Despite these brave efforts, the technology just wasn’t there yet.

In 1887, a German artificial eye maker started making contact lenses out of glass. The lenses covered all available parts of the eye, including the whites. The glass was heavy, no oxygen could pass through it, and wearers could not close their eyes over the lenses. As you might imagine, these contacts could only be worn for a few hours at a time before they became excruciatingly painful.

In 1936, the first plastic contact lenses were produced, which were much lighter and safer than glass contact lenses. However, they still covered the entire eye and were made of a hard plastic that didn’t absorb water and didn’t allow much oxygen to pass through. Thus, they were only comfortable for short periods of time.

In 1948, a manufacturing mistake led to the discovery that contact lenses covering just the cornea (the colored part of the eye) would stay in place while the wearer blinked and looked around. These smaller lenses were far more comfortable. In 1971, the first contact lenses made of soft plastic were introduced. They were even more comfortable and allowed oxygen to reach the surface of the eye. Today, more than 90% of contact lens prescriptions are for soft lenses. Manufacturers continue to make improvements to glasses and contacts for health, comfort and style.

More than 700 years after their invention, glasses are perhaps more essential than ever. By allowing people to easily read, write and learn, corrective lenses have undoubtably contributed much to new technologies being developed to maintain, restore and enhance our senses.

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