Base curve radius
（重定向自Base curve）
Base curve radius, or simply base curve, abbreviated BCR or BC, is the measure of one 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 (abbreviated BCOR). Typical values for a contact lens are from 8.0 to 10.0 mm. The base curve is the radius of the sphere of the back of the lens that the prescription describes. This number is important in order to allow the contact lens to fit well to the wearer's cornea for comfort, to facilitate tear exchange, and to allow oxygen transmission.