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Preschool and school-age childrencontact are a significant improvement over lenseses for children and adolescents who participate in sports or outdoor activities.contact are recommended for most athletes who need corrective eyewear. Often, a single pair of lenses is less expensive than the combined cost of glasses and prescription goggles. Swimmers especially can benefit from being able to see underwater while wearing regular goggles over their contactsbiforcal contact. Because contact tend to dry the contactsbiforcal eye, swimmers and all athletes should take care to blink several times before and after an activity session in order to assure natural cleansing. If any pool water enters a swimmer''s eyes, the lenses should be thoroughly disinfected contactsbiforcal as soon as possible to remove pool contaminants. Children who like spending time looking into a telescope, microscope, or binoculars may also prefer contacts over lenseses. Glass was the first material to 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 contactsbiforcal 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 contactsbiforcal 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 plastics used for lenses, and even higher than glass. contactsbiforcal Patients with high prescriptions should ask about high index material options for their lenses. Aspheric lenses are also useful for high prescriptions.
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