What Is a Contact Lens Base Curve?

Designed to fit on the cornea (the front surface of the eye), contact lenses are made to certain specifications that allow them to fit comfortably, correct vision, and sit in the proper place. Base curve is one of those important specifications.

Significance

• When you have your eyes examined for contact lenses, the eye doctor uses a machine called a keratometer to measure the curves of your eye. Your doctor uses these numbers to help determine the proper contact fit. The base curve is a measurement of steepness of the contact lens.

Soft and Hard Contacts

• Both soft and hard contact lenses have a base curve. Although the material they're made of differs, both types of lenses are designed to fit on your eye in a similar way.

Base Curve Numbers

• Measured in millimeters, base curve numbers usually range from 8.0 to 9.7. The lower the number, the steeper the curve of the lens.

Location

• Your contact lens prescription may contain several different types of numbers. Base curve is usually one of the first numbers specified on a contact prescription and is sometimes written as BC or B.C.

Considerations

• Some contact lens prescriptions may not specify a base curve measurement. In this case, the contact lens manufacture makes only one base curve, and the doctor does not need to differentiate the steepness of the lens.