No matter how perfect your period clothing, your perfectly coiffured hair, your well crafted head covering, wearing large modern frames destroys that impression completely.
Historically most people didn't wear spectacles (eyeglasses). They were a sign of weakness and old age. Most people lived with their impaired vision unless they could afford spectacles. Then they usually bought a ready made pair from an eye glass salesman. In many cases people never knew they were not seeing clearly.
When looking for period specs here's a simple guide for 1849:
For more details of the late 19th century see Spectacles.
Oval lenses, rectangular or oblong lenses are fine when they have the right temples. The best is octagonal appearing by 1840. Round Lens shapes where from before 1760 up to 1820. View this Ingres pencil drawing of 1819. These round lenses never came back until about 1910.
Temples are the clue to the age of the spectacles in most cases. For
Gold Rush period, and the most common samples surviving is the short lived
design of the
loop to loop slider
(1840 to 1880). Next were the pin & slot slider (1790 to after 1870).
long straight temple design 1820 to 1880). Pre 1850 are the short and straight temples and the hinged at center style. From 1770 to 1900 there was the "turn pin" style.
Any spectacles that have the wrap around the ear or riding bow
style, date after 1890 to present!*
The temples aren't complete unless they also have a "final" which is the end design.
Temple finals vary also! Three common styles in the Gold Rush; flat beavertails (1770 to 1900), small open teardrops (1820 to 1890), and medium open teardrops 1790 to 1850) The others are: large round open rings (before 1750 to 1800), small round open rings (1790 to 1830), large open teardrops with wider temples (1770 to 1830).
The connecting hinges where the temple connects to the lens frames will be bulkier in early styles. Most spectacles made before 1860 were hand crafted and numbers may be found stamped on the edges near the hinge that give the salesman a clue to what eye problem the individual may have. Some lenses may even be etched with a number as well.
Colored glass was used and usually for special reasons. The "D" frame glasses with side lenses that swivel to the front are usually dark blue or black and were made for people riding the trains in the 19th century. Green also seems to be surfacing.
This is not the last word on the subject, only a guide. I found much of my research after looking at many original spectacles owned by Jim Miller, William Dunniway and other friends as well as listening to their "expertise" and research from the books listed below.
Buying antique specs and fitting your lens use to be much cheaper than what you pay for modern specs. However today there are better looking specs made that have the look of the old samples and if you removed the nose guards could pass. I suggest no glasses are better than the wrong ones.