This is how I designed 3d printed frames around lenses that can be made by any optometrist!
I replaced broken my broken glasses by 3d scanning my lens using my phone's camera and Autodesk's 123D Catch. You can see the instructable here: https://www.instructables.com/id/3d-scanning-a-gla... , but you can order lenses from a variety of sources and download 3d models to design around. Check out http://www.eyewearkit.com/ for a place to start.
I used the 3d scan of my lenses as a reference to design my new frames in Rhino. This will require some moderate 3D modeling skill, but the process can be applied to almost any 3d software and can be very simple.
If you are working with a downloaded 3d file, much of this wont apply to you, but may come in handy to know.
Since I am working from a 3d scan, I have to start by importing my 3D scan and rotating it so that is in the right orientation. You can trim off the excess mesh around your lens by drawing a closed curve around it and using a mesh split.
Next scale your lens to the right dimensions. You can either measure it with calipers, or look at the inside of your glasses to find the sizes. The first number is the width of your lens, the second is the distance between lenses, and the third is the length of the arms.
Move your scan so that it is offset from the origin the correct amount. Since glasses are symmetrical, you only need to model half of them.