|
|
Rimless frames are the least noticeable type, and they are lightweight because the nosepiece and contactsbylensexpress temples are attached directly to the lenses, eliminating the weight of the rims. They tend to not 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 titanium and titanium alloy. Until the late 1980s, when titanium-nickel alloy and titanium frames were introduced, metal frames were, in general, more fragile than plastic frames. The titanium frames, however, 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 expensive. They are flatter and lighter than conventional lenses.There are many lenses and lens-coating options for individual needs, including coatings that block the ultraviolet (UV) light or UV and blue light which have been found to be harmful to the eyes. Such coatings are not needed on polycarbonate lenses, which already have UV protection. UV coatings are particularly important on sunglasses and ski goggles. Sunglasses, when nonprescription, should be labeled with an indication that they block out 99-100% of both UV-A and UV-B rays. There are anti-scratch coatings that increase the surface hardness of lenses (an important feature when using plastic lenses) and anti-reflective (AR) coatings that eliminate almost all glare and allow other people to see the eyes of the wearer. AR coatings may be particularly helpful to people who use computers or who drive at night. Mirror coatings that prevent other people from seeing the wearer''s contactsbylensexpress eyes are also available. There is a whole spectrum of tints, from light tints to darker tints, used in sunglasses. extended lenses in particular pose a much greater risk than daily wear lenses. Though extended-wear lenses are extremely thin and allow some oxygen--necessary for healthy eyes--to reach the cornea, they are worn continuously, including at night while the eyelid is contactsbylensexpress closed. Bacteria can easily grow more easily under these conditions. Twenty-one in 1,000 extended lens wearers develop infections as opposed to 4 in 1,000 daily soft lens wearers. To reduce this risk, eye care professionals now recommend removing extended lenses at night. In addition, newer versions of extended lenses contactsbylensexpress being developed may offer increased oxygen exchange and pose less risk. Disposable lenses may also help to prevent infection, since the wearer is guaranteed a clean pair of lenses every few weeks contactsbylensexpress or every day contactsbylensexpress.
|