As technology advances, so do lenses. In the past, they were made exclusively of glass. Today, most are made of high-tech plastics. These new ones are lighter, don’t break as easily as glass, and can be treated with a filter to shield your eyes from damaging ultraviolet (UV) light. The following lenses are lighter, thinner, and more scratch-resistant than glass or the older plastic types. Polycarbonate.
http://www.webmd.com/eye-health/eyeglasses-eyes
When buying eyeglasses, the frame you choose is important to both your appearance and your comfort when wearing glasses. But the eyeglass lenses you choose influence four factors: appearance, comfort, vision and safety. Eyeglass lens thickness is determined in part by the size and style of the frame you choose.
http://www.allaboutvision.com/lenses/how-to-choose.htm
These lenses reduce glare from a surface like water, so they’re great for sports and driving. But they can make it hard to see the liquid crystal display on your car’s dashboard. Your unique vision problem will determine the shape of your lens. You’ll need a concave lens (curves inward) if you’re nearsighted.
http://www.webmd.com/eye-health/eyeglasses-eyes
There is no major difference in principle between a lens used for a still camera, a video camera, a telescope, a microscope, or other apparatus, but the detailed design and construction are different. A lens might be permanently fixed to a camera, or it might be interchangeable with lenses of different focal lengths, apertures, and other properties.
https://en.wikipedia.org/wiki/Camera_lens
A camera lens (also known as photographic lens or photographic objective) is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically.
https://en.wikipedia.org/wiki/Camera_lens
The lens usually is focused by adjusting the distance from the lens assembly to the image plane, or by moving elements of the lens assembly. To improve performance, some lenses have a cam system that adjusts the distance between the groups as the lens is focused.
https://en.wikipedia.org/wiki/Camera_lens
Learn about the different types of lenses, and which is best for your eyes. Lens Types. Introducing 1-Day Acuvue Define contact lenses. We now carry 1-Day Acuvue Define contact lenses, for people who want to enhance their eye's natural beauty.
https://www.1800contacts.com/connect/lens-types
Glass lenses. In the early days of vision correction, all eyeglass lenses were made of glass. Although glass lenses offer exceptional optics, they are heavy and can break easily, potentially causing serious harm to the eye or even loss of an eye. For these reasons, glass lenses are no longer widely used for eyeglasses.
http://www.allaboutvision.com/lenses/how-to-choose.htm
Depending on the type of lenses and lens treatments you choose and the lens design you need, your eyeglass lenses can easily cost more than the frames you choose — even if you choose the latest designer frames.
http://www.allaboutvision.com/lenses/how-to-choose.htm
Types of simple lenses. Lenses are classified by the curvature of the two optical surfaces. A lens is biconvex (or double convex, or just convex) if both surfaces are convex. If both surfaces have the same radius of curvature, the lens is equiconvex. A lens with two concave surfaces is biconcave (or just concave).
https://en.wikipedia.org/wiki/Lens_(optics)
types of  lenses
Polycarbonate lens is one of the type of lenses. One of the types of lenses is Polycarbonate.