I don't think I've ever written about this, but it keeps coming up lately.
I wear glasses, and have since the third grade. I'm nearsighted, which means that the further away things are, the more out of focus they are. My own hand gets blurry around the edges (it's still clearly a hand, people, it's just a little out of focus) at full extension. I don't know my exact prescription off the top of my head.
I tried contacts briefly in high school, and hated them. Too much effort, too little reward. When wearing glasses has been part of your identity for most of your life, saying "you don't have to wear glasses" doesn't really click. At least, it didn't for me.
The upshot of this is is that I never wear my glasses when I train. Maybe if I was doing solo kata, or learning a lift where I wasn't putting out a lot of effort, but any serious effort or training, and the glasses come off.
For some reason, this seems to blow people's minds. I have no idea why.
Look, it's a fight, not a reading contest. I don't have to be able to read the fine print. I have to be able to see your head, hands, legs...it's all big enough stuff that I don't need to worry about fine details. (Especially since I'm trying to let my peripheral vision do a lot of the work anyway).
That's just at striking ranges. Grappling? I can see just fine, thanks. Sometimes, I can see more than I want to (tighten up that gi, partner).
I've fenced, boxed, kickboxing, grappled, done scenario work (including work in High Gear), all without my glasses on. Never once has my "poor vision" actually inhibited me. I guess if I take up shooting, it could be an issue, but that's about it.
There is, admittedly, a partly tactical consideration to this (or there was when I started). Swatting off my glasses was a favored tactic of middle school bullies, and I figured that in a real fight, that'd be the first thing a lot of people would do. So I learned to deal with it. Now, I don't even think about it.
Anyway: if you wear glasses or contacts, try going without them sometime. It might not be as bad as you think.
If you don't wear glasses: people, glasses don't equal blindness. I'm not crippled, nor am I fucking Daredevil. Get over it.