Im a bit late to the party, but I have an interesting answer. Yes I can blur my eyes, but I can ALSO do magic eye very well. These are two different things.
Focusing on one spot, like to view magic pictures, makes everything blurry except what you're focusing on. This can be done at any distance but is faster up close because as your eyes constrict, there is less in the field of vision to blur out.
Blurring my vision makes everything blurry including what youre focusing on. I do it best when the item im looking at is within 3ft of my face. I notice it most with words. I used to be able to do this at long distances however due to degeneration of my distance vision, its difficult to tell whether or not im doing it.
I have incredible control over all (ALL) of my ocular muscles. I can intentionally turn my eyes in different directions at the same time. I can watch two different people doing two different things in two different locations at the same time. I feel the muscles stretching and pulling. It doesn't hurt, but it does feel weird. It is not the same feeling as blurring my vision, but it is the same as when I try to focus on somethig that's inches away from my face. Definitely a muscle strain.
Either way, focusing to blur and voluntarily bluring are two completely different things.