I wanted to see if you absolutely needed to use clear lenses or if you could make a brooch with sunglass lenses too. So I tried two methods, one of which will work for sunglasses.
I had to twist the frame at the bridge a little bit to get these ones to budge as these were thick plastic frames, and the lenses were pretty thick too due to my strong prescription!
The next step is to choose the pattern or design for your brooch by cutting out a piece or pieces of scrap or decoupage paper to fit the shape of your lens.