Eyeglasses
Eyeglasses are optical devices consisting of specially shaped glass or plastic lenses mounted in a frame, primarily used to correct various vision problems. They serve a dual purpose, as they can also function as fashionable accessories regardless of whether vision correction is necessary. The history of eyeglasses dates back to the thirteenth century in Italy, where the first crude lenses were made from natural crystals. Demand for eyeglasses surged in the 1400s with the rise of literacy following the invention of the printing press. Over the centuries, significant advancements improved their design and functionality, including the development of bifocals by Benjamin Franklin in the 18th century.
Common vision issues requiring corrective lenses include myopia (nearsightedness), hyperopia (farsightedness), and presbyopia (age-related difficulty focusing on nearby objects). While myopia typically affects children and may be influenced by educational practices, hyperopia is often present from birth, and presbyopia typically develops in middle age. Nowadays, there are also over-the-counter reading glasses for those with presbyopia. Recent innovations include research on self-focusing eyeglasses that adjust to the distance of objects, enhancing clarity for wearers. Overall, eyeglasses have evolved significantly and remain essential tools for millions of people worldwide in managing their vision.
Eyeglasses
Eyeglasses are specially shaped glass or plastic lenses mounted into a frame that holds the lenses in front of a person's eyes. They are generally used to correct various types of vision problems, although some people wear eyeglasses as fashion accessories when no vision correction is needed. Obtaining prescription eyeglasses usually requires a visit to an ophthalmologist or optometrist, medical professionals who care for eye conditions, but some eyeglasses can be purchased at drug stores or other retail locations.
Brief History
Vision problems have likely existed as long as humans have, but the earliest use of eyeglasses most likely occurred during the thirteenth century. Between 1268 and 1289, someone in Italy shaped natural crystal into a lens intended to help correct vision. These early lenses were far from perfect; the crystal was heavy and had to be held up to the eye, and the methods for shaping the lenses were relatively crude, limiting their effectiveness.
By the 1400s, there was a growing demand for eyeglasses, especially among scholars, monks, and others who had an interest in reading. The development of the printing press in the 1440s made reading material more readily available, further increasing the demand for vision correction devices. Once technology improved to eliminate bubbles and other imperfections in glass, people discovered how to shape the material to form a usable lens. This solved the weight problem, but there were still issues. Early glass lenses refracted, or bent, light at odd angles, creating a rainbow-colored ring around the objects wearers looked at. Around 1730, a British lawyer and inventor named Chester More Hall combined two forms of glass to make a lens that eliminated this distortion.
During the 1700s, demand for eyeglasses spread across the Eurasian continent. This led to many improvements. For instance, the first eyeglasses were essentially two circular lenses held together by a frame of leather or metal, held in place by hand or balanced on the nose. Scissor eyeglasses had a spring-activated hinge in the middle and pinched down on the nose to hold the glasses in place. It was not until around 1728 that someone added earpieces, which are known as temples. In 1784, American inventor and diplomat Benjamin Franklin developed bifocals, or eyeglasses that correct for both myopia (nearsightedness) and hyperopia (farsightedness).
The nineteenth century saw additional improvements to the quality and availability of eyeglasses. During this time, the number of people wearing eyeglasses increased. Luckily, relatively inexpensive eyeglasses were available in general stores and sometimes from peddlers' wagons
During the twentieth century, Englishman Sir William Crookes developed sunglasses. Various other designs briefly came into use, such as pince-nez glasses, which had wire frames that perched on the wearer's nose, and the monocle, which was worn in front of one eye and held in place by slightly closing the surrounding facial tissue. Plastic lenses also came into use, making eyeglasses even lighter while also allowing for more variety in styles and colors. In addition, new techniques were developed to hide the lines separating the lenses in bifocals, to protect lenses from scratching, and to allow lenses to change tint according to the available light.
Reasons for Eyeglasses
People wear corrective eyeglasses for various reasons. The most common vision problems that require corrective lenses include myopia (nearsightedness), hyperopia (farsightedness), and presbyopia, or age-related difficulty focusing on close objects. These conditions are called refractive errors because they result from the way the visible light focuses on the retina inside the eye.
A person with myopia can see objects that are close, such as a book, but has trouble seeing faraway objects, such as a television screen or classroom blackboard. Myopia is often diagnosed in school-aged children, and it is thought that the tendency to develop nearsightedness may be inherited. Over the years, however, researchers have noticed that children who live in countries that place a high emphasis on education are more likely to develop nearsightedness. This has led to a theory that close work, such as reading, may increase the likelihood of developing myopia. According to Popular Science, it is estimated that one-third of the world's population will be affected by myopia by 2020.
Hyperopia, or farsightedness, occurs when people can see objects that are far away but have trouble seeing things nearby. People with hyperopia can drive easily without eyeglasses but may require them for reading and other close work. Farsighted individuals generally have the condition at birth.
Presbyopia is an age-related condition that affects the eye's ability to focus on close things. It generally begins to develop around age thirty-five and becomes noticeable sometime in a person's forties. People with myopia and hyperopia need an exam by an ophthalmologist or optometrist to determine the correct shape and thickness of the lenses needed to correct their vision. However, people with presbyopia can buy eyeglasses to help with reading at drug stores and other retail outlets because these glasses just use magnifying lenses to increase the size of print in books.
Some people might require a combination of corrective lenses. For example, a nearsighted person may need eyeglasses to drive and later develop presbyopia, which makes reading difficult. Bifocal eyeglasses, with small lenses to correct the presbyopia set into larger lenses that correct for distance, would be prescribed in this case. Eyeglasses can also be prescribed to treat other conditions, such as astigmatism, a refraction error that causes images objects to appear bent or bowed.
Topic Today
In 2016, researchers in Israel announced that they were working on developing self-focusing eyeglasses, according to Scientific America. These "omnifocals" use technology similar to a cell phone camera lens to send an infrared signal from the eyeglasses to an object. The signal is used to determine the distance to the object and make minute adjustments to the thickness of liquid crystals in the lenses. This allows the lenses to adjust the way light travels through them to the eye so the wearer sees the object correctly. According to researchers, the reaction happens at about the same speed that a normal eye would make the adjustment.
Bibliography
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A Moment of Science Staff. "A Brief History of Eyeglasses." Indiana Public Media, 27 Sept. 2003, indianapublicmedia.org/amomentofscience/a-brief-history-of-eyeglasses/. Accessed 4 Oct. 2016.
Ossola, Alexandra. "Why Are So Many People Nearsighted?" Popular Science, 18 Mar. 2015, www.popsci.com/why-are-so-many-people-nearsighted. Accessed 4 Oct. 2016.
"Timeline of Eyeglasses." Museum of Vision, American Academy of Ophthalmology, www.museumofvision.org/exhibitions/?key=44&subkey=4&relkey=35. Accessed 4 Oct. 2016.
Waldron, Patricia. "Why Nerds Need Glasses." Inside Science, 9 July 2014, www.insidescience.org/news/why-nerds-need-glasses. Accessed 4 Oct. 2016.