What does the Base Curve (BC) of a contact lens indicate?

The Base Curve (BC) of a contact lens refers specifically to the central curvature on the back surface of the lens, which is designed to fit the shape of the eye. This measurement is critical for ensuring proper fit and comfort, as it influences how the lens sits on the cornea and the overall visual acuity experienced by the wearer.

The Base Curve is usually expressed in millimeters and is chosen based on the individual curvature of the patient's cornea. A properly fitted BC helps in maintaining adequate tear exchange under the lens, which is important for eye health and comfort over time.

Understanding the other options highlights why they are not correct. The thickness of the lens is a different measurement that affects the weight and comfort of the lens. The diameter of the lens is a separate parameter that defines the overall size and coverage of the lens on the eye. Lastly, the color of the lens is unrelated to the Base Curve and pertains to cosmetic or visibility features of the lens. Therefore, identifying the Base Curve accurately is essential for optimal fitting and performance of contact lenses.