Choosing the right size
If you have an old pair of glasses that look good, you can easily use the measurement information stamped on them. Usually the information you need is on one of the arms or inside the bridge.
The measurements need not be exact, but the closer they are to those of your old glasses, the more the new ones will look similar on your face.
A. Eye (diameter of the lense measured in millimeters)
: The lens diameter is the width of the lens, measured from the bridge
B. Bridge (width of bridge measured in millimeters)
: To determine the correct size of your sunglasses, you need the width of the bridge, which determines how the glasses rest on your nose.
C. Temple (measured in millimeters)
: The length of the temple is the length of the frame's arms from the front of the frame to the temple which secure the frame behind the ears.
The base curve represent the degree of curvature of the lense. The numbers that are high represent a lense that is more curvy over the eye compare to a smaller number which will be less curved (ex: 6 is less curved than the 8).