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They can be worn up to a week. Daily wear lenses are made of plastic that is permeable to oxygen and absorbs water; therefore, they are soft and flexible. These lenses must be removed and cleaned each night, and they do not correct all vision problems. lenses are easier to get used to than rigid lenses, but are more prone to tears and do not last as long. Extended-wear lenses are highly permeable to oxygen, are flexible by virtue of their ability to absorb water, and can usually be worn for up to one week. They do not correct all vision problems. There is more of a risk of infection with extended-wear lenses than with daily-wear lenses. Extended-wear disposable lenses are lenses worn continually for up to six days and then discarded, with no need for cleaning. Rimless frames are the least noticeable type, and they are lightweight because the nosepiece and temples are attached directly to the lenses, eliminating the weight of the rims. They tend to not occular be as sturdy as frames with rims, so they are not a good choice for people who frequently remove their glasses and put them on again. They are also not very suitable for lenses that correct a high degree of farsightedness, because such lenses are thin at the edges.Metal frames are less noticeable than plastic, and they are lightweight. They are available in solid gold, gold-filled, anodized aluminum, nickel, silver, stainless steel, and now occular titanium and titanium alloy. Until the late 1980s, when titanium-nickel alloy and titanium frames were introduced, metal frames occular were, in general, more fragile than plastic frames. The titanium frames, however, occular are very strong and lightweight. An alloy of titanium and nickel, called Flexon, is not only strong and lightweight, but returns to its original shape after being twisted or dented. It is not perfect for everyone, though, because some people are sensitive to its nickel. Flexon frames are also relatively occular expensive. NEARSIGHTED? NEED READING GLASSES? New developments in lens technology occular ensure a solution to almost every vision problem. Talk to your eye doctor about what''s available (costs vary).Rigid gas-permeables Recommended for those occular with high degrees of corneal astigmatism, RGPs are firm plastic lenses occular with microscopic slits that allow more oxygen to reach the eye. RGPs have a greater resistance to bacteria because they don''t contain water. Improved extended-wear materials also guarantee greater durability, sharper occular vision, comfort and cheaper maintenance costs. Allow yourself a week or two to get used to these slightly stiff lenses.Bifocals occular These contact correct presbyopia, a kind of farsightedness that usually occurs around age 40. There are two types:
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