Sunglasses are more than just a fashion statement -...
If you have hard resin lenses (CR-39), you should consider getting a scratch-resistant coating. Resins and plastics are more susceptible to scratches than glass. Scratches damage the cosmetic look of the lenses and compromise their performance. With a scratch-resistant coating, you do not have to worry as much about minor scratches on your lenses.
Another advantage of scratch-resistant coatings is that most coatings come with a one-year warranty. They are a great investment to prevent minor scratches. However, it is important to remember that scratch-resistant does not mean scratch-proof. All lenses are susceptible to scratches.