If you are having trouble visualizing these oversized sunglasses, think of Elvis Presley. Elvis wore the sunglasses that were popular during the late 70s and early 80s. His favorite style seems to have been the aviator shape glasses. Aviator glasses are in the shape of a right triangle with the corners well rounded. The glasses are wider at the outer edge of the face and narrower toward the nose. The lenses are basically a straight line across the top.
Another popular style had rectangular lenses. These glasses were often curved to fit around the face, but the basic shape was that of a rectangle. Of course, once again corners of the rectangle were rounded off. Another variation of the rectangle was the square glasses.
A final shape of oversized sunglasses that deserves mention here are the round sunglasses. They were not as popular for as long and were worn only by a few people. However, there were round oversized sunglasses as well.
While metal frames had become popular in the late 60s with the rise of the Beatles, their use seems to have become less popular with the popularity of the oversized glasses. The oversized sunglasses used plastic frames. With the plastic frames, the most popular were the white or black, although there was a while that these frames featured paint splatters to break up the color.
When looking for oversized vintage sunglasses, you will find that there are new sunglass style that have been set aside for years that have been brought back out for sale. Additionally you will find many replicas of the oversized vintage sunglasses as well as new designs that may have never actually surfaced during the vintage years.
If you want authentic oversized vintage sunglasses, your best bet is to shop at thrift stores or estate sales. If you want replica glasses you may find many options in your local boutiques. If you do not find what you are looking for, be sure that you also check online.