Ionizing radiation from tinted single vision spectacle lenses

Some ophthalmic lenses are tinted using materials which contain trace amounts of thorium or daughter products of the thorium and uranium chains. Such lenses emit small amounts of ionizing radiation. No tissue damage has been proven as a result of wearing these eyeglasses. Still, any radiation exposure is a potential hazard. Since there are many essentially nonradioactive lenses on the market, tinted lenses containing thorium contaminants would seem to represent an unnecessary risk.