In reply to:

But his real brillance was in discovering that vision was extremely susceptible to mental strain. So, it does change a lot during the course of a day, even for people with normal sight, depending on the stress the person is under.



That is so true. I've noticed that when I'm stressed out and don't wanna do anything but just go home and relax, my vision gets very blurry, to the point where I have trouble reading billboards on the highway or reading a license plate 20 feet away. But when I'm well rested, very relaxed, and I can very easily concentrate, then my vision is perfect.