They are flatter and lighter than conventional lenses.There index and contact 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 lenses not needed index on polycarbonate lenses, which already have uv protection. uv coatings are particularly important on sunglasses and ski goggles. sunglasses, when contact nonprescription, should be labeled with an indication lenses that they vision block out 99-100% of both uv-a and uv-b rays. there are contact anti-scratch coatings that increase the surface hardness of lenses lenses (an important feature when using plastic lenses) and anti-reflective vision and contact (ar) coatings that eliminate almost all glare and allow other people to see the eyes of the wearer. ar coatings may be particularly lenses helpful to people who use computers or who drive at night. mirror coatings that prevent other people from seeing the wearer''s eyes are also available. there is a whole spectrum of tints, vision from light tints to darker tints, used in sunglasses.
plastic contact frames are durable, can accommodate just about any lens prescription, and are available in a wide range of prices. they are also offered in a variety of plastics (including acrylic, epoxy, cellulose acetate, lenses cellulose propionate, polyamide, and nylon) and in different colors, shapes, vision and levels of resistance to breakage. epoxy frames are resilient and return to their original shape after being contact deformed, so they do not need to be adjusted lenses as frequently as other types. nylon vision frames are almost unbreakable. they revert contact to their original shape after extreme trauma and distortion; because of this property, though, they cannot be readjusted after they are manufactured.fit the patient should have the distance between the eyes (pd) measured, so that the optical centers of the lenses will be in front of the patient''s pupils. bifocal heights also have to be measured with the chosen frame lenses in place and adjusted on the patient. again, this is so the lenses will be positioned correctly. if not positioned correctly, the patient may experience eyestrain or other problems. this can occur with over-the-counter reading glasses.