Yes, what your mom tells you is right. With the modern life develop fast, the electric products will have bad effect on the eyes. The too much time use of computers, television and so on may make the eyes feel uncomfortable. When you look at the screen, the distance is so near that will save the procedure of reflecting the light resource into the corneal and then coming to the eyes. If you play nintendo 3ds for a long time, your eye nerves will intense which will easily feel tired. If you are doing so for a long time, your eye vision may get worse. What's worse, the brain will get tired. It is easy to get shortsightedness. Thus, you should not play it for a long time, having a little rest for the eyes after 40 minutes looking at the screen.