Calling the eye doctor is the best idea. If that's not possible, take a look at http://www.randolphusa.com/GWW-RandolphEngineering/DisplayPage.aspx?pageid=232. Figure out which frame you have, and measure it with the lenses installed. My standard 68mm Ranger frame measures 135mm, outside edge to outside edge, just like that chart says. Also, my 68mm lenses measure 68mm across, from notch to notch (outside edge).