Almost all spectacle lenses produced now are made from plastic. Not only is this much safer than glass, they are also much lighter.
The draw back with a plastic lens is that it scratches much easier than glass and so care must be taken to clean them with a correct cloth and spray and ensure that they are stored properly in a case when not in use.
can be applied to plastic lenses to protect them. These do toughen the surface greatly, but do not make the lens
entirely scratch proof.