How do they make glass for eye glasses?

Spectacles are made from very special glass and ordinary window glass just will not do. Subjects that concern vision and the improvement of sight are called optics. And the lenses used in eye glasses to correct or improve the vision are made of optical glass. The basic ingredients are sand, soda and lime, as in ordinary window glass. But the materials must be quite free from impurities and the molten brew must be made again and again to remove all blemishes. Manufacturers have thousands of recipes for making different kinds of glass. Traces of several ingredients may be added to give clarity and hardness to a hatch of optical glass. Finally the crystal clear material is ground and shaped into lenses to fit each person's spectacle prescription. The same type of optical glass is made into curved lenses for microscopes and telescopes.  more