BC for contacts stands for "Base Curve." It is a measurement that refers to the curvature of the back surface of a contact lens—the side that touches your eye's cornea. The base curve is important because it determines how well the lens fits the shape of your eye. A proper fit ensures comfort, proper vision correction, and eye health. The base curve is measured in millimeters and typically ranges from about 8.3 mm to 9.0 mm for soft contact lenses. A lower BC number indicates a steeper curve (for a more curved cornea), while a higher BC number means a flatter curve (for a less curved cornea). Eye care professionals measure your corneal curvature during an eye exam to determine the most suitable base curve for your lenses. Wearing lenses with the correct base curve prevents discomfort, slipping, and vision problems, and helps maintain proper oxygen flow to your eyes. In summary:

• BC = Base Curve
• It measures the curvature of the contact lens's back surface
• It must match your eye's corneal shape for comfort and effectiveness
• Typical BC values range between 8.3 mm and 9.0 mm
• It is a critical part of your contact lens prescription

This measurement is essential for ensuring comfortable wear and good vision correction with contact lenses. Ill-fitting base curves can cause discomfort, poor vision, or even eye damage. The BC is usually found on your contact lens prescription and lens packaging labeled as "BC" or sometimes "BOZR" (base optic zone radius). If you need details on what your BC number might be, it is determined by your eye doctor using a tool called a keratometer during your eye exam.