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Base curve radius (BCR) or simply base curve (BC) is the measure of an important parameter of a lens in optometry. On a spectacle lens, it is the flatter curvature of the front surface. On a contact lens it is the curvature of the back surface and is sometimes referred to as the back central optic radius (BCOR). Typical values for a contact ...
Diameter and base curve radius. The parameters specified in a contact lens prescription may include: Brand name; Material; Base curve radius (BC, BCR) Diameter (D, OAD) Optical power in diopters (dpt) Center thickness (CT) Prescriptions for contact lenses and glasses may be similar but are not interchangeable.
Normal contact mechanics or frictionless contact mechanics focuses on normal stresses caused by applied normal forces and by the adhesion present on surfaces in close contact, even if they are clean and dry. Frictional contact mechanics emphasizes the effect of friction forces. Contact mechanics is part of mechanical engineering.
Thus the base curve defines the front surface of the main part of the lens while the back surface geometry is changed to achieve the desired distance power. The "bifocal" is a third spherical segment, called an add segment , found on the front surface of the lens.
A rigid gas-permeable lens, also known as an RGP lens, GP lens, or colloquially, a hard contact lens, is a rigid contact lens made of oxygen-permeable polymers. Initially developed in the late 1970s, and through the 1980s and 1990s, they were an improvement over prior 'hard' lenses that restricted oxygen transmission to the eye.
Lens clock. A lens clock is a mechanical dial indicator that is used to measure the dioptric power of a lens.It is a specialized version of a spherometer.A lens clock measures the curvature of a surface, but gives the result as an optical power in diopters, assuming the lens is made of a material with a particular refractive index.