|These glasses have built in prisms, which bend the light path by 90 degrees. So instead of looking ahead, you are looking down! Or, as the blurb says, if you are lying down in a horizontal position, on a sofa or on a bed, you will be looking towards your feet! You could use them to read a book or watch tv while lying down. So they can also be called Lazy Glasses! The manufacturer advises against wearing these while walking or in motion generally, as you can become disorientated. We were very impressed with the build quality of these glasses, which are very solidly made. Also the prisms appear to be made of glass, as far as we can tell.The glasses come in a variety of colours.