<unk> , or simply<unk><unk> , abbreviated BCR or BC, is the measure of an important parameter of a lens in optometry. On a spectacle lens, it is the flatter<unk> ture of the front surface. On a contact lens it is the<unk> ture of the back surface and is sometimes referred to as the back central optic<unk>  (abbreviated BCOR). Typical values for a contact lens are from 8.0 to 10.0 mm. The<unk><unk>  is the<unk>  of the sphere of the back of the lens that the prescription describes (the lower the number, the steeper the<unk>  of the cornea and the lens, the higher the number, the flatter the<unk>  of the cornea and the lens). 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. The United States Food and Drug Administration states that, "Contact lenses can be used to correct a variety of vision disorders such as Myopia (nearsightedness), Hyperopia (farsightedness), Astigmatism, and Presbyopia (poor focusing with reading material and other near vision tasks)."
Base curve radius
Tidal volume
Extraction ratio
NC ratio
Peak kilovoltage
Equivalent air depth
E/A ratio
End-systolic volume