I'm no optician but I sometimes notice similar affects when working from my desktop for a few hours and then using my smaller phone which requires a different focus.
Intuitively it feels like my eyes remain adjusted to looking at a screen even after I'm no longer looking at a screen hence the blurryness which occurs.
The regular breaks and looking out of the window far away are good advice.
I just discovered this little software today and I'm liking it so far. It will beep and black out your screen, forcing you to take a break which is also important for circulation to your legs.
I was getting blurry vision when I wore my regular glasses to correct nearsightedness in front of the computer all day. Switching to reading glasses made it much better.