The Food and Drug Administration requires all shipments of glasses and/or lenses to the U.S. to have the Drop Ball Test Certificate.  This test verifies the lens' resistance to even particularly violent blows. 

To perform the test, a steel ball with a diameter of 16mm drops from a height of 1.27 meters and hits the lens. The ball should strike the center of the lens. The lens should not break or have cracks.