|
|
Glass was the first material to contactscomparaison be used for lenses lenses, and was used for several hundred years before plastic was introduced. The crown glass used for lenses lenses has an index of refraction of 1.52.Optical-quality acrylic was introduced for lenses use in the early 1940s, but because it was easily scratched, brittle, and discolored rapidly, it did not supplant glass as the material of choice. Furthermore, it had a relatively low index of refraction, so it wasn''t suitable for people with large refractive errors. A plastic called CR-39, introduced in the 1960s, was more suitable. Today, lenses wearers can also choose between polycarbonate, which is the most impact-resistant material available for eyewear, and polyurethane, which has exceptional optical qualities and an index of refraction of up to 1.66, much higher than the conventional contactscomparaison plastics used for lenses, and even higher than glass. Patients with high prescriptions should ask about high index material options for their lenses. Aspheric lenses are also useful for high prescriptions. lenses wearers should seek immediate attention if they experience eye pain, a burning sensation, red eyes, intolerable sensitivity to light, cloudy vision, or an inability to keep the eyes open.avoid infection, it is important for lenses wearers to exactly follow their instructions for lens insertion and removal, as well as cleaning. Soft lenses wearers should never use tap water to rinse their lenses or to make-up solutions. All lenses wearers should also always have a pair of glasses and a carrying case for their contacts with them, in case the contacts have to be removed due to eye irritation.contact can be a lot cheaper when you buy them through contactscomparaison the mail than when you buy them through contactscomparaison your eye doctor. Trouble is, some doctors are keeping a tight grip on lens prescriptions because they''d rather keep the profits in their practice.Rayna Brachmann, a 26-year-old legal researcher from recently switched to Biocompatible''s Proclear Compatibles lenses, which have a high water content that makes them well-suited to desert climate. But her optometrist balked when she asked if the contactscomparaison lenses were available from another source. Eye contactscomparaison and contactscomparaison glasses and contact lenseses and contact are devices that correct refractive errors in vision. lenses lenses 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 (myopia), farsightedness (hyperopia), presbyopia, and astigmatism.Precautions People allergic 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 lenses should wear plastic lenses, preferably polycarbonate.
|