ECO Shades Size Guide
The lens diameter (eye size) is the width of the lens measured from the bridge. It may be a matter of personal preference, but it's also determined by the design of the frame.
The width of the bridge is the distance between the lenses over your nose. It's important that it's comfortable - if it's too tight, the glasses will pinch your nose, and if it's too loose, the glasses won't sit stably on your face.
The length of the temples should be long enough to sit comfortably over your ears.