When I first got into muzzleloading in the early 70's, we HAD to buy original frames and get our prescription lenses put in them. We didn't have as much documentation on what was correct back then and the link I posted in the above reply demonstrates how we were often off by a couple to a few decades for what was authentic to the pre or Revolutionary war era. Fortunately, there has been much more authentic documentation come out and even more importantly, authentic reproductions made.
My first pair of spectacles was of the 1790 to 1810 period, though we thought they were earlier back then. I lost them somewhere and my second pair were of the 1820 to 1840 period, because that's what I could find in the antique shops. Some day a future Archaeologist will find them in a dig near the original Union Gun Emplacements the VMI Cadets took at the Battle of New Market and if far enough in the future, it might cause a ruckus to future historians. I can see it now,
"AHA, here is an original example of prescription lenses made about 20 years before any documentation or example was known." Grin. I "took a hit" during the Reenactment and lost the spectacles and even though about 15 of us searched all over, we never found them.
Fortunately by the time I needed my next pair of period eyeglasses, G.Gedney Godwin and Jas. Townsend had really nice authentic reproductions. I have the "blended" bifocals in mine so they "are authentic" or authentic enough for French and Indian War onward. I have only been challenged once on wearing them and that was ONLY at the EXTREMELY "authentic picky" event at Colonial Williamsburg when we do the weekend "Under the Red Coat" where the British Army took over Williamsburg on the way to the eventual surrender at Yorktown. (I was then 49 or 50 and very old for a Private Soldier in the Major's Coy, 42nd Royal Highland Regiment and yes, we know they weren't with General Cornwallis's Army, but that's another matter, grin.)
When the Inspecting Officers came round, my own Captain asked about why I had such fancy shoe buckles. They weren't fancy, they were almost exactly the same as the standard severely plain soldier's shoe buckle, but mine had to be a bit bigger because I have such large feet and the very slightly smaller ones hurt my feet. I've always called my feet, "Stable Gun Platforms." Grin. I explained that with over three decades of service, I had gambled and wenched most of my income away, so I decided I would buy a slightly neater set of buckles to have something to show for long service. Both Inspectors chuckled at that and said, "Well, can't argue with that." Then the other inspecting officer asked how I could afford GOLD spectacles? I told him they weren't gold, but rather polished brass to match the polished brass on my Musket, shoe buckles and other brass items. I further told him I had tried steel frames, but they rusted too easily and weren't "Soldierly Enough." I also told him I would not have used silver frames, even if I could have afforded them, because someone might think I was trying to falsely appear to be a Commissioned Officer or one of my betters." The Major replied, "Well done, Private. You are correct not to attempt to emulate your betters." My Captain just kind of rolled his eyes and had a wry grin on his face.
My Captain had retired from the modern Army as a "Mustang" Captain and of course he knew I had retired as a Master Gunnery Sergeant of Marines. Later on when we were alone, he told me Marines were known for good BS, but that was the best case of "period BS" he had ever heard. This in a jesting manner of course. Trying to look the innocent, I asked him if there was anything period incorrect with my answers. He replied, "Well, no there wasn't." Then I replied, well, what we also reenacted (though we had not intended it) was how an experienced enlisted man "got over" on his officers. Since he had been both enlisted and an Officer, he got a good laugh out of that. But I digressed....
From actually wearing them so much, I can highly recommend these spectacles from G. Gedney Godwin and they CAN be fitted with safety glass lenses. The lens size is big enough it offers some pretty good protection to your eyes. They are also large enough lenses for those of us used to modern eyeglasses that you don't struggle with adjusting to them as much as some other period styles.
http://www.gggodwin.com/CartGenie/prod-286.htmAlso, Jas Townsend offers them and other styles. He has an excellent video on period spectacles including how to adjust them on this link:
http://jas-townsend.com/product_info.php?cPath=7&products_id=166However as Don and others have suggested, when shooting live rounds in "period" competition, I've never seen nor heard of anyone being denied the use of modern normal or safety glasses. They might ask you to take them off after you are done shooting in really authentic areas, unless you physically can't do without them. I did that on a few occasions until I could get period correct glasses.
