LENS DESIGN

BASE CURVE AND SECONDARY CURVE

Most contact lenses, rigid and hydrogel, are 
made with more than one curve on the back 
surface to fit the eye.  The central curve is 
called the base curve and the radius of this 
curve is called the base curve radius (BCR); 
back optic zone radius (BOZR); 
posterior central curve radius (PCCR) or 
back central optic radius (BCOR).

One or more curves with a longer radius 
(often referred to as a flatter radius) are 
added to the back of the lens towards the 
edge.  The first curve beyond the base 
curve is called the secondary curve and its radius is referred to as the secondary curve radius (SCR); posterior secondary curve radius (PSCR) or back peripheral optic radius (BPOR1).

If only 2 curves are on the back of the lens it is said to be a bicurve lens.