Prior to the Civil War, original eye glass frames were fastened with a molten lead plug. During the Civil War, Americans used screws to fasten eye glass frames allowing prescriptions and lenses to be replaced.
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.