Scratch resistant coating
All plastic lens materials are significantly softer and more easily scratched than glass, if not coated with a hard, scratch-resistant layer. The coating is made of a much harder plastic compound to provide an added level of scratch protection that rivals glass. But it too can eventually become scratched over time. Once scratched, a lens cannot be repaired or “buffed” to remove the scratch. No scratch coating alone can be guaranteed not to scratch; it is simply added protection from scratches. However, if you are extra hard on your glasses, or you are buying for your kids, consider investing in a replacement program.
Anti-reflective (AR) Coating
An AR coating consists of multiple microscopic layers applied in a vacuum, on either the front surface or both surfaces of the lens, to virtually eliminate light reflections. This helps to improve visual contrast and clarity. AR coating is very helpful to reduce glare during night driving and computer work. An AR coating also makes it easier for other people to see your eyes behind the lenses. Reducing reflection is especially important if you’ve chosen a high index lens because without it, they can reflect up to 50% more light than a CR-39 lens, causing significantly more glare.
Now, when thinking of AR coatings, you must compare apples to apples…and there are some rotten ones out there! Point being, not all ARs are created the same. If you opt for a cheap AR coating (one thing you can’t get here), it can become scratched and damaged very easily. This will cause your vision through the lenses to be worse than if you had opted out on the AR all together. So go all in or leave it off!
Because there are fewer reflections, sometimes fingerprints seem more visible on the lens. High grade AR coatings are easier to clean than the others. Be sure to use an official cleaning cloth and cleaning fluid approved for AR coatings.
Ultraviolet blocking protection
The sun radiates ultraviolet waves, which are extremely damaging to the human eye and skin. Over time, its accumulation can lead to cataracts and even macular degeneration. That’s why it’s important to protect your eyes, starting in childhood. Lenses with ultraviolet protection help prevent harmful UV radiation from reaching your eyes. Polycarbonate, high-index, sun-sensitive photochromic, and polarized lenses all have built-in UV protection. Only CR-39 plastic lenses need an additional coating for UV protection.
Be careful out there: http://www.allaboutvision.com/sunglasses/spf.htm
Photochromatic treatment allows your lenses to darken in response to UV light, and then automatically return to clear when indoors. This technology has seen dramatic improvements over the past several years, related to how dark they get and how clear they get. However, keep in mind that when you are driving, the windshield blocks out much of the UV light, thereby reducing the stimulus for the lenses to darken. There are photochromatic treatments specifically designed to turn dark in the car, however this version will not turn completely clear indoors. Photochromatic treatments are now available in virtually all lens materials and designs, and in multiple colors.
Consider this: http://www.allaboutvision.com/lenses/photochromic.htm