We read in a recent report that 1 in 10 people can't see 3D properly, but there have been concerns that even those who can see 3D images could suffer from eye strain and poor vision from playing the console too much. As such, Nintendo recommends children under the age of 7 do not play 3DS with the 3D effect on to prevent any possible issues, which may be a smart move according to University of Cambridge expert Neil Dodgson.
With regard to children under seven [playing 3DS], the answer is that we just do not know whether they will have a particular problem or not. We will only really know if there is a problem if we get a spate of cases where young adults find that they have eyesight problems that can be statistically correlated with excessive use of 3D at an earlier age.
Of course, no ethically-minded company is likely to endorse the kind of research and experimentation that could answer this question conclusively, so it seems prevention is the best option. Could Nintendo include a parental option to switch the 3D effect off entirely? Only time will tell. If this speculation hasn't put you off Nintendo's next handheld, be sure to check out our 3DS Hands-On to see what all the fuss is about.