Almost everyone wears glasses at some point in their lives. In developed countries, the rule of thumb is that around 70 percent of adults need corrective lenses to see well. And over the last generation, just two companies have risen above all the rest to dominate the industry. The lenses in my glasses — and yours too, most likely — were made by Essilor, a French multinational that controls almost half of the world's prescription lens business and has acquired more than 250 other companies in the past 20 years. There is a good chance, meanwhile, that your frames were made by Luxottica, an Italian company with an unparalleled combination of factories, designer labels, and retail outlets.