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Base curve (BC) is the curvature of the back surface of a contact lens. Measured in millimeters, it matches the curve of your cornea. A correct base curve supports comfort, clear vision, and healthy oxygen flow.
read more about base curve in optics ...Base curve guides how the lens sits and moves on your eye.
During a contact lens fitting, your eye doctor measures the curvature of your cornea using a tool called a keratometer or corneal topographer. These readings help select a base curve that aligns with your eye shape. Trial lenses are often used to confirm how the curve behaves on the eye before finalizing your prescription.
Do not change base curve on your own. Your eye doctor measures corneal curvature and selects a lens that fits your eye and the way a brand behaves on the eye. A different curve can feel tight or loose, shift more, and blur vision. Follow your prescription to keep fit and comfort steady.
Base curve is the back surface curvature and relates to how the lens hugs the cornea. Diameter is the edge to edge width and relates to coverage and position. Both values work together to keep comfort and vision stable.
A poor base curve fit often shows up as comfort or stability problems. If you notice any of the signs below, schedule a refit with your eye doctor.
Look for BC followed by a number such as 8.6. It appears near power and diameter.
Stick to the curve your doctor prescribes. Even small differences can reduce comfort or clarity.
Most soft lenses fall between about 8.3 and 9.0. Your doctor will set the curve that fits your eye.
If you are looking at your prescription and cannot find the base curve, or if you feel your current lenses are sliding too much or feel excessively tight, contact your eye care provider. A precise fit is necessary to prevent corneal molding or oxygen deprivation, which can only be assessed during a professional fitting.