Bausch & Lomb Inc. is selling its sunglass business, which includes the Ray-Ban brand, for $640 million to Luxottica Group S.p.A. of Italy. Bausch & Lomb, based in Rochester, controls around 40 percent of the global premium-sunglass business, which also includes brands like Revo, Killer Loop and Arnette. But its sunglass unit has struggled of late to turn a profit as rivals like Oakley Inc. gained with styles aimed at young customers. Bausch & Lomb shares fell $1, to $78. Luxottica, which owns the Lenscrafters retail chain, makes eyeglass frames in the medium- and premium-priced categories with brand names like Giorgio Armani, Brooks Brothers, Vogue and Anne Klein.