The Tonus 18-21 mmHg (Moderate Grade Class I) Knee High Medical Compression Stockings with OPEN Toe, MODERATE Grade Class I is a compression support for foot and ankle varicose veins and the prevention, rehabilitation and treatment of chronic venous insufficiency, such as heavy foot syndrome and edema. Compression stockings increase blood flow and prevent swelling, especially during long flights - flat seams for maximum comfort - heel area is fortified to extend the durability of the product - made of tested and certified medical compression materials.