It was not meant to be a joke, it happens to me every time when using my iphone for ~20 or more minutes, after which my vision is so very blurred that i almost can't use the normal desktop monitor until my vision gradually gets back to normal, over 10-15 minutes.. I tried holding the phone further or closer, it still happens.
Like i said, it is a bit of a wild theory, only backed by what we learned in school about the eye's properties.
Sadly the straining effect is also backed by many other posts on different websites, where lots of people report they started having eye problems after starting using retina monitors or tablets. It is true that there are also other people saying it is actually better for the eyes, i am not sure each in what percentage, but there seamed to be a lot of people With problems. Check out also this thread on apple forums:
[Update: links not allowed, so you can search for the name of the thread: "Retina Display MacBook Pro eye problem and strain"]
Sorry if I seamed a bit too sure on what i was saying in the first post, I don't want to be an alarmist, but it is better that to check on these things and find that it's all b.s., rather than duck up our eyes for good..