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&lt;A HREF=&quot;http://www.triopticaonline.com/gafas-online/&quot;&gt; Gafasonline&lt;/A&gt; , also known as eyeglass lenses , eyeglasses or spectacles , are an optical instrument consisting of a pair of glasses fastened to a frame that rests on the nose by a bow and two pins that help hold them in your ears.
They are a combination of two health products : lenses and optical mount that fits professional optometrist or a particular patient based on the correction required for each eye, the pupillary distance and the selected frame . It is mainly used to compensate defects of vision , such as nearsightedness , farsightedness or astigmatism , although there are special glasses to protect eyes in activities where there is a risk for these ( in this case if no optical correction they are not medical devices ) . Work by focusing light through the lenses to compensate for visual defects.
There are also bifocal glasses you combine two different lenses graduation in one , suitable for presbyopic patients allowing the user to see far and close , and trifocals see also allow an intermediate distance . The latter no longer used while bifocals are used less and less in favor of progressive lenses .
The earliest historical reference to the increase of view goes back to Egyptian hieroglyphics of V century BC, which represented simple glass lenses . The earliest written record of magnification view dates from the first century BC, when Seneca, a tutor of Emperor Nero of Rome, wrote: &quot; Letters, however small and blurry , are seen more widely and clearly through a globe or glass full of water ' .1 Nero also said he saw the gladiatorial games using an emerald as a lens corrector.2 using a convex lens for a wider image is discussed in Alhazen optics book ( 1021). His translation from Arabic into Latin in the twelfth century was instrumental to the invention of eyeglasses in Italy XIII.1 century
The treatise irride (&quot;In the rainbow &quot;) Grosseteste Robert English , written between 1220 and 1235, mentions using optics to &quot;read the smallest letters from incredible distances .&quot; A few years later , Roger Bacon also would be released for writing about the properties of lenses extending in 1262.3
[url=http://www.triopticaonline.com/gafas-online/]Gafasonline[/url] , in the form of flat crystals of smoky quartz , were used in China during the twelfth century . Similarly, the Inuit have used snow lenses for eye protection. However, while corrective offered no benefit , 4 really improved visual acuity narrowing the field visi&Atilde;&Acirc;&sup3;n.5 The use of the term &quot; sunglasses &quot; by historians is anachronistic before the twentieth century.