2 Answers

I worry about this too. My guess is, too much of anything can be harmful.  However, I think  these things numb your brain before affecting your eyesight.  I would worry more about what it is dong to your social skills.   I have seen people text each other from across the room. too lazy to walk over there. Or maybe their social skills are so bad they forgot how to communicate in person. Or never learned it in the first place.

I'm typing this in braille..........No I'm not really, and my sympathy goes out to people with sight problems, I've got a cataract and typing with one good eye, and one finger gets more difficult by the day,don't own a cell phone, can't see anything on them, Candy crush gets harder by the day.