HowStuffWorks "How Corrective Lenses Work": "Corrective lenses can be made with glass or plastic, but nowadays, plastic is the most common. While several different types of plastic are used in making lenses, all of them follow the same general manufacturing procedures. Most of the steps outlined also apply to glass, although a few important differences are noted at the end.
A lab, even an automated one, follows 12 steps to make prescription lenses:"
