Base curve radius

Base curve radius, abbreviated BCR or BC, is a parameter of a contact lens. Typical values are from 8.0 to 10.0 mm. The base curve is the radius of the sphere that the back of the contact lens describes. Contact lenses must fit well to the wearer's cornea in order to be comfortable and to facilitate tear exchange and oxygen transmission.

In everyday practice, if contact lenses feel "loose" and slide easily a smaller base curve may work better. A large base curve may be needed if they feel tight. Lenses with smaller base curves are referred to as "steep".