I never knew these existed, Chas., and my guess is that my eyes are much older than yours. I will have to look into them.
I have had a bad problem with astigmatism most of my life, and I learned many years ago of the little variable apertures to correct that situation where the front sight is concerned, and I have used one made by "Merit" in bullseye competition with both handguns and stock iron sights on long guns for at least 40 years. It sticks on the the lens (in my case the right one) with a small suction cup, and I put the aperture at the upper left-hand corner of the right lens, where the front sight falls naturally for me. This makes the front sight nice and crisp, leaving the target the fuzzy black ball many good shooters prefer, so as to avoid bouncing their focus back and forth between the front sight and the target, and overcoming any unhelpful distracting attempt to focus on the x-ring.
The variable aperture trick is of course of no value except in target shooting, which left me up to Mother Nature when practicing personal defense shooting, and a funny thing happened the other day. I had cataract surgery on my left eye (my "off" eye), and the lens implanted by the surgeon sharpened up my distance vision to 20/20 or better, but I still needed near vision correction for both eyes. I had always, having been a flier for many years, but no longer, used trifocals - one lens to see where I was going, another for the panel, and the third for the chart on my lap. After my cataract surgery my optometrist recommended, and prescribed, two pairs of bifocal glasses -- one for distance vision and reading, and the other for use at the computer and reading. They work as intended.
An unintended consequence is that wearing the "computer glasses" I find I can do away with the variable lens most of the time when handgun target shooting, and they work fine for personal defense practice -- for a simple reason: my computer monitor happens to sit a a distance from my eyes very close to the distance from my right eye to my front sight with a handgun at arm's length.
I am back to the variable aperture of course for iron-sight rifles, but all this reminded me that if money is not an object a competent optometrist can prescribe glasses which focus sharply for you at any distance you might desire.
I'm relatively new here on your forum, as contrasted with being a long-time CHL holder, and this, I think, is my first chance to say "Howdy," and compliment you on what has to be a time-consuming job for you, but so valuable to the rest of us.
All the best,
We're not going to reason people out of positions they haven't reasoned themselves into, to paraphrase Ben Franklin.