No eyeglass lenses — not even glass lenses — are scratch-proof.
However, lenses that are treated front and back with a clear, scratch-resistant coating have a much harder surface that is more resistant to scratching, whether from dropping your glasses on the floor or occasionally cleaning them with a paper towel.
Kids' lenses, especially, benefit from a scratch-resistant hard coat for greater durability.
Today, most eyeglass lenses, including high-index lenses and lenses made of polycarbonate and Trivex, have a built-in scratch-resistant coating.
Since scratch-resistant coatings are sometimes optional, make sure your optician knows that you want your eyeglass lenses to include hard coating for extra durability. Also, ask about the warranty on eyeglass lenses that are treated with scratch-resistant coating versus those without the coating.
Keep in mind that even the best scratch-resistant coating can't completely protect your lenses from wear and tear. To keep your glasses looking new, store them in a cushioned case when not in use, and clean your lenses with a microfiber cloth and the cleaning solution your optician recommends.
Also, be wary of products that promise to repair scratched lenses. These products may fill in the scratches, but it is impossible for them to make the scratches disappear so the lenses look new again.