Base curve radius, or BCR, is a parameter of a contact lens. Typical values are from 8.0 to 10.0 mm. The base curve is the radius of the sphere that the back of the contact lens describes. Contact lenses must fit well to the wearer's cornea in order to be comfortable and to facilitate tear exchange and oxygen transmission. A contact lens (also known simply as a contact) is a corrective, cosmetic, or therapeutic lens usually placed on the cornea of the eye. ... The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber, providing most of an eyes optical power [1]. Together with the lens, the cornea refracts light and, as a result, helps the eye to focus. ... Tears are commonly associated with crying Tears are a liquid produced by the bodys process of lacrimation to clean and lubricate the eyes. ...
In everyday practice, if contact 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
Contact Lens Prescriptions Explained (detailed article about contact lens prescriptions)
The second curve is the reverse or return zone which is approximately 0.6mm wide and steeper than the basecurveradius by two to 2.6 times the amount the basecurve is flatter than K, and can range from 6.00D to 12.00D steeper than the basecurveradius.
The outer curve of the lens is the peripheral curve, which is very similar to the peripheral curve of the three-zone design; it is most commonly 0.4mm wide with a radius of curvature of 10.50mm to 12.50mm.
Basecurveradius determination is accomplished by fitting the lens flatter than K by the amount of desired refractive change +0.75D.
The primary curve on the posterior surface of a RGP lens is the basecurve.
The ideal basecurve relationship on a cornea with with-the-rule corneal astigmatism exhibits alignment or slight apical clearance across the central cornea and along the flatter horizontal meridian.
The sole function of the flatter peripheral curves is to provide clearance as the lens moves across the flatter portions of the cornea with lateral gaze and blinking.
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