Glasses, known formally as eyeglasses, are frames with lenses. They are worn in front of the eyes with support from the nose and ear. Their primary purposes are to correct vision and protect the eyes. They are also worn as a fashion statement. Eyeglasses, safety glasses and sunglasses are the common types.
Egyptian hieroglyphs are the earliest historical reference to magnification. In 1270, Chinese people, specifically the rich and old, were reportedly wearing spectacles. A painting done by Tommaso da Modena in 1352 is thought to be the earliest pictorial evidence of eyeglass use. There are different theories as to who should be credited with the invention of specs, as we know them today.
A common use for spectacles is vision correction. Spectacles have the ability to correct refractive errors within the eye. This is possible by modifying the focal length of the lens. Traditional spectacles can alter the focal point to correct visions in area. Changing the extent of curve, thickness or shape of the lens can shift the focal point. Specs are known to alleviate conditions such as astigmatism, nearsightedness, farsightedness, presbyopia and myopia. Another form of corrective spectacles is pinhole glasses. These specs do not use a lens, do not refract light and do not change focal length. Still, they correct refractive errors of the eye.
Safety glasses are used to protect the eye from flying debris or chemicals. Typically these items are constructed from plastic and have lenses that are impact resistant. At their thinnest point they are usually a minimum of one millimeter thick. Polycarbonate is often used in production of these specs. These are commonly used in factories, industrial work and laboratories.
Sunglasses are often used for aesthetic purposes, to hide eyes, improve visibility in the sunlight and reduce glare. They can contain a prescription lens. The dark lenses are helpful in protecting against visible light or ultraviolet light. Lenses can come in a variety of colors, shapes and sizes.
Three-dimensional glasses are used to create the illusion of three dimensions when viewing movies or items with images that have been prepared in a special way. Classically they had one red lens and one cyan or blue lens. When the lens is polarized it can make colors appear to be three-dimensional.
Reading specs are usually for people who do not normally need to wear spectacles. They contain lenses that magnify. The magnification is preferred for close-up reading. Generally a prescription is not needed for these specs. They can be purchased tried on and purchased at the store. The levels of magnification are generic. These are sometimes used to treat cases of presbyopia and hyperopia. There are two main styles: full frames and half-eyes. Full frames are typically the size of normal eyeglasses, while half-eyes contain thinner lenses.
Individuals who have trouble focusing may be recommended a multifocal lens. Bifocals and trifocals are the most common forms of these lenses. These specs have two or three horizontal viewing areas in the lens that allow wearers to change focus without changing glasses. Many prefer no-line bifocals because they offer a nice transition between the various focal areas.
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