Wearers of spectacles or contact lenses have a lens between their eyes and whatever they are focussing on nearly all the time during their waking day. It doesn't cause eyestrain and I've always been assured by optometrists and maybe once an ophthalmologist that wearing lenses for myopia doesn't worsen myopia: iirc it's focal distance that matters, and apparently the Rift keeps the focal distance at infinity. Of course Oculus is talking its book, but I'd be surprised if they have no-one who understands the ophthalmology of the lenses-and-screen configuration they're building into their product.
I'm not an optometrist/ophthalmologist by any stretch, so I can't comment on the physiology, but I can say that the most remarkable thing about the Oculus experience is the sensation of infinite depth -- and infinite depth 360 degrees around you.
I think this is the really surprising thing for people who haven't tried it before -- you think it will be like looking at a screen up close, since you've looked at screens your whole life, but it's nothing like that at all.
