---Thickness: Polycarbonate has a higher index of refraction than Trivex (1.58 vs. 1.53), so polycarbonate lenses are about 10 percent thinner than Trivex lenses
---Weight: Polycarbonate lenses are lighter than glass lens, so polycarbonate is more comfortable to wear for long periods of time
---Impact resistance: Polycarbonate lenses are highly resistant to impact, won’t shatter, and are 10 times stronger than glass or standard plastic, making them ideal for children, safety lenses, and physical activity
---UV protection: Polycarbonate lenses can block 100 percent of the sun's UV rays without the need for special UV-blocking lens coating
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Bifocal lens can be called a multi purpose lens. It has 2 different fields of vision in one visible lens. The larger of the lens usually has the prescription necessary for you to see for distance. However, this can also be your prescription for computer use or intermediate range, as you would normally be looking straight when you view through this particular part of the lens. The lower part, also called the window, typically has your reading prescription. Since you generally look down to read, this is the logical place to put this range of vision assistance.