johnson and johnson surevue

Another type of multifocal, a trifocal, has an area in-between that corrects for intermediate distances (usually about 28 in). Conventional bifocals and trifocals have visible lines between the areas of different correction; however, johnson lenses where the correction gradually changes from one area to the other, and without visible lines, have been johnson available since the 1970s. Such lenses are sometimes called progressives surevue and johnson and and or no-line bifocals.To johnson be suitable for lenses lenses, a material surevue must be transparent, without bubbles, and have a high johnson and and index of refraction. The greater the index of refraction, the thinner the lens can be. Lenses are made from either glass or plastic (hard resin). The advantage of plastic is that it johnson is lightweight and more impact resistant than glass. The advantage of glass is that it is scratch resistant and provides the clearest possible vision.

extended lenses in particular pose a much greater risk than daily wear lenses. Though extended-wear lenses are extremely thin and allow surevue some oxygen--necessary johnson for healthy and eyes--to reach the cornea, they are worn continuously, including at night while the eyelid is closed. Bacteria can easily grow more easily under these conditions. Twenty-one in 1,000 extended lens wearers develop johnson infections as opposed to 4 in 1,000 daily soft lens surevue wearers. To reduce this risk, eye care professionals now recommend removing extended lenses at night. In addition, newer versions of extended lenses being developed may offer johnson increased oxygen exchange and pose less risk. Disposable lenses may also help to prevent and infection, since the wearer is guaranteed a clean johnson pair of lenses every surevue few weeks or every day.

Glass was the first material to be used for lenses lenses, and was used for johnson 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 and and johnson introduced for lenses use in the early 1940s, but because it was easily surevue 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 johnson 1960s, was more suitable. Today, lenses wearers can also choose between polycarbonate, which is the most and and johnson impact-resistant material available for eyewear, and polyurethane, which has exceptional surevue optical qualities and an index johnson and and of refraction of up to 1.66, much higher than the conventional plastics used for lenses, and even higher than glass. Patients with high prescriptions should ask about high index material johnson options for their lenses. Aspheric lenses are also useful for high prescriptions surevue.

©2003 www.contacts-soft-colored.com. All rights reserved.