Does anyone know the history of why we changed from circular glasses to the general shape of today? (more rounded on bottom, flatter on top)

I'm curious why the change was made and why this particular shape. I know you can find frames in a variety of shapes, but prevailingly most of them that aren't gimmicky are a bit longer and rounder on the bottom and flatter on the top. Does this have to do with range of vision? Is it purely aesthetic? Anyone know?