An alternative material to polycarbonate is CR39 (Columbia Resin 39), a plastic polymer commonly used in the manufacture of eyeglass lenses. Unlike polycarbonate, CR39 requires a UV coating to be added to protect eyes from the sun’s harmful rays.
Who makes Definity lenses?
Essilor
Essilor manufactures optical lenses under the Varilux®, Crizal®, Thin&Lite®, DEFINITY™ and other Essilor brand names.
What is the difference between polycarbonate and CR-39?
Polycarbonate lenses have a higher index of refraction (1.586) than CR-39 plastic (1.498) and are therefore thinner in an equal lens prescription. With a higher index (of refraction), light is bent more efficiently, therefore it requires less material to achieve the eyeglass prescription making the lenses much lighter.
