How would I go about about making wraparound glasses? I apologise if this is not the right place to ask, but I am relatively new to this website. 
I want to make a pair of sunglasses, that look like this.
As you can see, there is a round curve on the glasses, and I have attempted to follow tutorials on regular glasses which do not help, as I'm unsure on how to create the 'curve' effect that the image above has.

Any suggestions or advice would help greatly, thank you.
I think I'm not that an expert. But if you can look up if this helps:
1. Take a cube.
2. Subdivide it or put a subsurf modifier.
3. Put a cast modifier.
4. Apply those.
5. Cut the sphere using  the frame of the sun-glass frame with boolean modifier.
                 .................hope this helps...............
P.S. remember to adjust the radius so that the glass doesn't look too bulky..