Originally Posted by alliswell
Is the "bridge" measurement on a sunglass frame a reliable guide to fit? I have a Persol frame with a 16mm bridge which slips on my nose; should I stay away from anything 17mm or larger?
Depends how it is slipping. If the side of the pads are not touch and it is sliding down, stay away from anything that is wider. If they are touching but sliding down changes are it just needs an adjustment. If you get a dispenser to adjust them they may be able to help the fit a bit.
The "bridge" measurement is NOT a fool-proof measurement. Usually a "17" bridge can be an actual "16.5mm" or "17.5". It isn't a big difference, but if you consider 16.5 and 17.5, it is a difference of 1mm. In the eye world, that is huge. We measure things in factions of millimeters. When lenses are cut they are to the 100th of a millimeter. So that should give you an idea of the specifics in eyewear.
I know I kind of gave a vague answer. But if you have another specific question, let us know.