Oval, rectangular and round frame eyeglasses have competed with one another for ocular dominance in America since its founding. Round frames were considered ‘out of style’ by the end of the Revolution War (possibly due to their victory over England), to be replaced by rectangular frames. In turn, the rectangular frames lost out to oval frames around 1860; however, round eyeglasses were still in existence during the American Civil War.
These are, of course, only general guidelines. Thus, though not prevalent, some round frames were made during the Civil War. Likewise, although the rectangular frames went out of style by 1860, some people would have continued to wear such frames.
Compared to modern eyeglasses, antique spectacles are very small. Lens grinding technology was the limiting factor in determining the size of early spectacles. Limited technology, coupled with the size of the average person in the mid-1800’s combined to give people who wore spectacles an appearance indicative of that period; a defining frame-to-face ratio. Today we are physically larger than we were in the 1800’s and original period spectacles are just too small for most of us.
A good rule of thumb for spectacle size is approximately two-thirds the width of the face, eyes centered horizontally in the lens portion of the spectacles. As we are physically larger today than in the past, spectacle sizes can be increased to comfortably fit the wearer, while maintaining the approximate frame-to-face ratio of the past.