Maybe my experience with this problem would be useful for middle-aged (and older) eyeglass wearers.
I was born nearsighted, and for a good many years I built models with no magnification. (I needed glasses to recognize a human being from across a room, but had no trouble seeing fine details close-up.) Recently, though, I've been having a little trouble with short distances. My 54-year-old eyes, without the help of glasses, can focus simultaneously only at a distance of about a foot and a half.
I've tried Opti-Visors at various times, but I've never been able to get along with them. There seem to be two problems. One - when I look through an Opti-Visor I lose some of my depth perception. (I have trouble judging, for instance, how far the tip of a paint brush is from what it's about to paint.) Two - like most other people, I have two eyes with significantly different characteristics. The right and left lenses of an Opti-Visor are identical, so if one eye is in focus the other one isn't.
The answer turned out to be simple. Several tool dealers, including MicroMark ( www.micromark.com ) and Woodcraft ( www.woodcraft.com ) sell magnifiers that clip onto regular eyeglasses - the same way "clip-on sunglasses" do. They flip up out of the way when you don't need them. Your regular glasses take care of the difference between the right and left eye, so both are in focus. At least in my case, depth perception doesn't seem to be a problem (probably because I'm so accustomed to working with my regular glasses). And these things are surprisingly cheap: between $10 and $15.
I'm sure this solution won't work for everybody, but I urge those who wear glasses to correct significantly different right and left eyes to give it a try.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.