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Preschool and school-age childrencontact are a significant improvement contacts 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 color from being able to see underwater while wearing regular goggles over their contact. Because contact tend to dry the eye, swimmers and all athletes should contacts take care to blink several times before color 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 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. Originally, hard contact were made of a material called PMMA. Although still available, the more common types of contact are listed below:Rigid gas-permeable (RGP) daily-wear lenses are made of plastic that does not absorb water but allows oxygen to get from the atmosphere to the cornea. (This is important because the cornea has no blood supply and needs to get its oxygen from the atmosphere through the film of tears that moves beneath the lens.) They must be removed and cleaned each night. Rigid gas-permeable (RGP) extended-wear lenses are made from plastic that also does not absorb water but is more permeable to oxygen contacts than the plastic used for daily-wear lenses. Another type of multifocal, a trifocal, has an area in-between that corrects for intermediate distances color and contacts (usually about 28 in). color Conventional contacts bifocals and trifocals have visible lines between the areas of different color correction; however, contacts lenses color where the correction gradually changes from one area to the other, without visible lines, have been available since the 1970s. Such lenses are sometimes called progressives or no-line bifocals.To be suitable contacts for lenses lenses, a material must be transparent, without bubbles, and have a high index of refraction. The greater the index of color refraction, the thinner the lens contacts can be. Lenses are made from either glass or plastic (hard resin). The advantage of plastic color is that it is lightweight contacts and more impact resistant than glass. The advantage of glass is that it is scratch resistant and provides the clearest color possible vision.
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