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.
In science, work and energy are commonly measured in joules. One joule is the amount of energy it takes to lift an object that weighs one Newton a one meter distance. A Newton is the metric unit for weight and is comparable to the weight of a stick of butter.