I think most programmers don't realize how much vision holds them back. I've been coding blindfolded for over a month and I'm never going back. If you are a touch typist what do you need to see ? Not looking at things helps me to focus. I do take the blindfold off while checking my work an during some parts of debugging.
Not to take anything away from this, because it is impressive, but a lot of people overestimate how much you need to look at your code while writing it. That's because we've gotten used to (if we are older programmers) or grown up with (if we are younger programmers) editors on big screens or in big windows that always show us a lot of our code.
There was a time when that was not the norm. Many programmed on teletype terminals or on 24x80 character CRTs that did not have cursor addressing (AKA "glass TTYs"), usually connected to the computer over a slow serial line (300 baud for a hardcopy terminal was typical). Text editors worked a line at a time. You could see whatever previous lines had not scrolled off the top yet. Best case, that would show you the line you were typing and 23 prior lines, although usually some of those lines would be showing editing commands you typed rather than lines of your code. If you wanted to see more lines, you had to type a command to tell the editor to show them, and they would come in from the bottom, scrolling prior stuff off the top.
In that kind of environment programmers tended to do a lot more of their work in their heads than we do now. Not as much as a blind person has to do, of course, but a lot more than seems feasible to the average programmer nowadays. Heck, it often seems infeasible nowadays to many of us who programmed back then. I know I wrote a lot of code in such environments, but nowadays I cannot figure out how the heck I actually was able to do that.
I'm not sure if we are actually better off now or not. We don't have to keep track of us much in our heads because our editors do it for us, so perhaps that frees up some brainpower to concentrate on more important things. On the other hand, maybe by keeping more of our code in our heads back then, we were able to understand it better.