After the news that the new 3ds is going to come out, i've recently heard a lot of people complain that the 3d feature is going to hurt your eyes. Sadly this is true, but dont worry im hear to give you tips on how to not loose your eyesight:
1) Use the 3d slider to lower or shutoff the 3d effects
2) Take a 5 minute brake after playing for 30 minutes on your 3ds with the 3d effects on
3) Shutoff the 3d effects after playing 30 minutes with the 3d effects on your 3ds
4) Only use the 3d effects in the cool parts of the game
5) Dont use the 3d effects at all for one day and use them on the next
6) Dont use the 3d effects when playing multiplayer in a game (chances are u are not going to stop playing)
7) If your head starts hurting stop playing, eat, or go outside and play
Dont use the 3d effects if your playing inside a moving car
9) Turn on the lights if your playing in a dark place (unless your outside at night, then go inside)
10) Listen to your parents if they tell you to stop playing your 3ds
Remember 3d effects are cool, but being unable to see them aren't, and even if you turn off the 3d effects you still got tose amazing 3ds graphics.