Base curve radius
Encyclopedia
Base curve radius or simply base curve, abbreviated BCR or BC, is the measure of one important parameter of a lens
Corrective lens
A corrective lens is a lens worn in front of the eye, mainly used to treat myopia, hyperopia, astigmatism, and presbyopia. Glasses or "spectacles" are worn on the face a short distance in front of the eye. Contact lenses are worn directly on the surface of the eye...

 in optometry
Optometry
Optometry is a health care profession concerned with eyes and related structures, as well as vision, visual systems, and vision information processing in humans. Optometrists, or Doctors of Optometry, are state licensed medical professionals trained to prescribe and fit lenses to improve vision,...

. On a spectacle lens, it is the flatter curvature of the front surface and on a contact lens
Contact lens
A contact lens, or simply contact, is a lens placed on the eye. They are considered medical devices and can be worn to correct vision, for cosmetic or therapeutic reasons. In 2004, it was estimated that 125 million people use contact lenses worldwide, including 28 to 38 million in the United...

 it is the curvature of the back surface. Typical values for a contact lens are from 8.0 to 10.0 mm. The base curve is the radius of the sphere of the back of the lens that the prescription describes. Contact lenses must fit well to the wearer's cornea
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...

 in order to be comfortable and to facilitate tear
Tears
Tears are secretions that clean and lubricate the eyes. Lacrimation or lachrymation is the production or shedding of tears....

exchange and oxygen transmission.

In everyday practice, if lenses feel "loose" and slide easily a smaller base curve may work better. A large base curve may be needed if they feel tight. Lenses with smaller base curves are referred to as "steep".

External links

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