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.
Mass is both a property of a physical body and a measure of its resistance to acceleration when a net force is applied. It also determines the strength of its mutual gravitational attraction to other bodies. The basic SI unit of mass is the kilogram. In physics, mass is not the same as weight, even though mass is often determined by measuring the object's weight using a spring scale, rather than balance scale comparing it directly with known masses. An object on the Moon would weigh less than it