Optical Service, a 20-year-old British company that sells about one million pairs of frames a year under 15 different house brands, has obtained a license for Schott eyewear that covers the U.K., the Baltic countries and South Africa, where it carries most of its export business through an export agent. The company is interested in marketing other brands in the U.K., where it employs eight full-time salespersons and offers next-day deliveries to just over 4,000 retails, 95 percent of whom are independents.