I have 3 thorium lenses by different manufacturers, but I don't have any concerns about them affecting my health. I believe the main reasons thorium stopped being used were 1, improvements in technology allowed other materials to be used in it's place, and 2, concern over worker's safety. It's true that thorium lenses put out too little radiation to do any harm, but the large amounts used in the manufacturing of the glass likely posed a greater health risk.