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Eye glasses and contact lenseses and contact are devices that correct refractive errors in vision. lenses lenses contacts are mounted in frames worn on the face, sitting mostly on the ears and nose, so that the lenses are positioned in front of the eyes. contact appear to be worn in direct contact with the cornea, but they actually float on a layer of tears that separates them from the cornea.PurposeThe purpose of lenseses and contact is to correct or improve the vision of people with nearsightedness discount and contacts (myopia), farsightedness (hyperopia), presbyopia, and astigmatism.Precautions People allergic discount to certain plastics should not wear contact or lenses frames or lenses manufactured from that type of plastic. People allergic to nickel should not wear Flexon frames. People at risk of being in accidents that might shatter glass contacts lenses should discount wear plastic lenses, preferably polycarbonate. contact The concept of corrective lenses that sit directly on the eyeball was developed in the ninth century, but it was not until the late 20th century that manufacturing and grinding techniques for contact were perfected. Originally contact were made of glass, then later of hard plastic, and still later of flexible, highly oxygen-permeable soft plastic. Today, the majority of lenses worn are of two basic types: rigid gas permeable (so-called contacts "hard" lenses) and lenses. best lenses are smaller and more durable, but require a longer period of adjustment for the wearer. Hard contact can correct some vision problems, like astigmatism, that the lenses cannot. discount The lenses are slightly larger contacts than best lenses. They are more comfortable and less expensive, but can be easily torn. The latest generations of contact are extended discount and disposable lenses. extended lenses are intended to be worn for several weeks at a time, while disposable lenses are thrown away every day or every few weeks, or in the newest versions, every day.
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