Nintendo has issued a warning on its blog that children six and under should not view the 3-D images that will come from Nintendo 3DS.

The Kyoto-based company posted a message on its Japanese language blog saying 3-D game play can cause eye fatigue. It says children six and under should not use 3-D games, since their eyes are not fully developed. It also says gamers of any age should not play the 3DS in 3-D mode for longer than 30 minutes at a time. For 2-D game play, Nintendo recommends breaks after an hour of play.

It isn't clear why the company didn't issue a release in English. Nintendo of America did not respond to requests for additional comment.

This is not the first time Nintendo has expressed concerns regarding the effects of 3-D on young eyes. In June, when the Nintendo 3DS launched at the E3 Conference, Nintendo president and chief operating officer Reggie Fils-Aime said the company would issue guidelines on healthy viewing.

We will recommend that very young children not look at 3D images, Fils-Aime said at the time. That's because, [in] young children, the muscles for the eyes are not fully formed. This is the same messaging that the industry is putting out with 3D movies, so it is a standard protocol. We have the same type of messaging for the [1990s Nintendo virtual reality machine] Virtual Boy, as an example.

Recently, a study from Clemson University psychologist Eric Muth said some video games, like the Kinect, that employ virtual reality could cause motion sickness. However, he said the risk of motion sickness in the Kinect was not very high.