In my mind, most of retro sunglasses were inspired in 1940s. So, i don't know what 1920s sunglasses look like till i search in Google. When i search 1920s in Google Images, It result me antique round sunglasses. Now, are you still plan to wear such antique sunglasses? Not all people can hold such round sunglasses. If you have a very round faces, you'd better choose other shaped retro sunglasses instead.
1920's style sunglasses are these glasses with round metal-framed lenses or the horn-rimmed round glasses. Now these 1920's style sunglasses become popular again in recent years. They are also called classic sunglasses or retro style sunglasses. Now more and more people follow the trend to get these retro style sunglasses to wear because they do add a chic item to their appearance. You may find the fashion glasses either in the vintage store or at the online optical stores.