What do the frame sizes mean and how are they measured?
The first measurement is the width of one of the lenses measured horizontally across the widest dimension. The second measurement is the width between the lenses also known as the bridge measurement. The third measurement is the length of the temple measured from the hinge to the end of the temple. Back when 6-base lens geometry ruled the world these measurements had real value as a comparison and fit tool. With the current move to 8-base lenses it is less reliable as some glasses wrap around the side of the head more than others. Just because one model has a temple length of 125mm and another 135mm doesnt mean one fits smaller than the other. In fact they both could fit the same. On metal frames with nose pads the bridge measurement is just a starting point as this is an adjustable component.
