LENS DESIGN

TERITARY CURVES

Additional curves beyond the secondary 
curve may be used.  The next curve is 
often called the tertiary curve and has 
a radius called the tertiary curve radius 
(TCR) or second back peripheral optic 
radius (BPOR ).  It is longer than the 
secondary curve radius.

Sometimes more than 2 peripheral 
curves are used.  Ones beyond the 
tertiary curve are often just numbered, 
such as 4th, 5th, etc.

The outermost curve (often the tertiary curve) may be very narrow, for example 0.1 mm or 0.2 mm wide.  When this outermost curve is narrow and has a long radius (11.0 mm or greater) it is often referred to as a bevel.