Although we call them "glasses," modern lenses are sunglasses factory
rarely made of glass. Of course, you can still get glass lenses by special order, but lenses these days are more commonly made of different types of plastic. Plastic lenses are safer and lighter than glass lenses.
If something breaks or shatters your glass lenses, it can be dangerous if this happens near your face and eyes. Unfortunately, the tradeoff is scratch resistance. Plastic is softer than glass and scratches more easily, making plastic lenses more prone to surface wear. For minor scratches, use a small microfiber cloth to clean the lenses.
Pinch the cloth between your thumb and forefinger and gently wipe the surface of the lens in circular motions. This alone can remove very minor scratches. You can also try water and a drop of mild dish soap when cleaning your glasses.
Dishwashing liquid is gentler than most cleaners, making it a safer option for deep cleaning lenses. Rinse and remove excess soap with a microfiber cloth and gentle circular motions. For smudges or other stubborn marks, a small amount of isopropyl alcohol can also be used. Again, a microfiber cloth and circular motions are the best way to clean.