Scleral lenses have gained popularity in the last decade. From a lens with limited viability for over 100 years to the fastest growing segment of the gas permeable lens market, scleral lenses have come a long way.
Mass and Weight. The mass of an object is a fundamental property of the object; a numerical measure of its inertia; a fundamental measure of the amount of matter in the object. Definitions of mass often seem circular because it is such a fundamental quantity that it is hard to define in terms of something else.
Weight is different from mass. Weight is the measure of the force of gravity on an object. The mass of an object will never change, but the weight of an item can change based on its location. For example, you may weigh 100 pounds on Earth, but in outer space you would be weightless. However, you will always have the same mass on Earth as you have in outer space.