suggests that heavy users are more likely to become nearsighted. researchers note that the most significant changes were reported in children and young adults. let's talk to dr. campbell, a practicing cardiologist and assistant professor of medicine at the university of income number. there's a 35% increase in nearsightedness and this is really picked up since the year 2007. explain why this is. >> what we have found is that when you use smart phones, you typically hold those tablets or smart phones or electronics very close to your face. 30 centimeters or more. with books you are using 40 centimeters and it puts a significant strain on the eyes which leads to nearsightedness. heather: is that something that can be fixed in any way? if you start holding those things farther away from your face, especially children, can you prevent nearsightedness? >> i think you can help. i think the biggest thing we can do is limit screen time. i think that the american academy of pediatrics recommends no more than two hours a day of