Scratch resistant coating: The plastic lens material is relatively soft and is easily scratched if it is not coated with scratch-resistant material. Even with scratch-resistant coating, your lenses will become scratched through normal use over time. The coating material is a much harder plastic compound that is applied to the lens, but it too can be scratched. once scratched, a lens cannot be repaired or “buffed” free of the scratch. Scratch coating can not be guaranteed; it is simply added protection from scratching, and it will inevitably scratch over time.
Mirror Finish: Mirror finishes are thin layers of various metallic coatings on an ordinary lens. Although they do reduce the amount of visible light entering your eyes, do not assume they will fully protect you against UV radiation.
Ultraviolet protection (UV): The sun radiates ultraviolet waves, which are extremely damaging to the human eye and skin. Lenses with ultraviolet protection help prevent the harmful UV radiation from touching your eyes. Polycarbonate, high-index, sun-sensitive photochromic, and polarized lenses all automatically contain UV protection. Only hard resin lenses need an additional coating to add UV protection.
Anti Reflective (AR) Coating is an extremely thin layer of film that is deposited on either the front or both the front and back surface of the lens that virtually eliminates light reflections. AR coating makes it easier for other people to see the wearer’s eyes, and it makes it easier for the wearer to see through the lens. AR coating is very useful for night driving and for people who look at computer screens. Lenses with AR coating must never be cleaned dry, as this can scratch the coating. The best cleaner is one that is made especially for AR-coated lenses.