This industry comprises establishments primarily engaged in one or more of the following: (1) retailing and fitting prescription eyeglasses and contact lenses; (2) retailing prescription eyeglasses in combination with the grinding of lenses to order on the premises; and (3) selling nonprescription eyeglasses. Grinding lenses without retailing lenses--are classified in U.S. Industry 339115, Ophthalmic Goods Manufacturing; The private or group practice of optometry, even though glasses and contact lenses are sold at these establishments--are classified in Industry 621320, Offices of Optometrists; and Retailing eyeglasses and contact lenses via mail-order--are classified in U.S. Industry 454113, Mail-Order Houses.