Eyeglass frames can hold a variety of lenses. Because people have different problems with their vision or require certain characteristics from their glasses lenses, eyeglass companies manufacture specific types of lenses to accommodate these needs. Polarized and polycarbonate lens types vary by shape and composition.

polycarbonate lenses are shaped like most other lenses in a spherical shape. Polarized lenses are also spherical. The difference is shape between the two lenses is that polycarbonate lenses are typically lighter than polarized lenses. In fact, some polycarbonate lenses are up to 35 percent lighter and thinner than regular plastic lenses, according to Frames Direct.

Polycarbonate lenses were the first plastic high index lenses. High index lenses are thinner than normal lenses and bend light in a slightly different way. Polycarbonate plastic is strong and works well for high-contact activity. Polarized lenses are also made of plastic, but they also contain a special filter that prevents "intense reflected light, reducing glare," according to All About Vision.

Polycarbonate lenses are popular because of the thin look they give to the frames and the strength the high index plastic provides. Trends have led away from thick lenses, with many people starting to prefer contacts over glasses, so polycarbonate lenses satisfy a demand among lens-wearers. Polarized lenses block out glare from the sun, enabling people to see more clearly. Photochromic polarized lenses also block out glare but also change from light and clear inside to a darker shade outside.

Lenses made of polycarbonate plastic are most often used in high-contact activities, like sports. Parents often buy polycarbonate lenses for their children, as kids are usually active and do not always take the best care of their glasses. Polarized lenses are popular for anglers who want to see more clearly into the water and do not want to experience the sometimes intense glare off the surface of the water. These lenses are also common for people who have to travel or drive a lot and do not want the glare of the sun through windshields.