Eye strain and blindness

Blue light from computer screens and digital devices can decrease contrast leading to digital eyestrain. Fatigue, dry eyes, bad lighting, or how you sit in front of the computer can cause eyestrain. Symptoms of eyestrain include sore or irritated eyes and difficulty focusing. Studies suggest that continued exposure to blue light over time could lead to damaged retinal cells.

Sleep Disturbance

More teens now sleep less than 7 hrs of most nights. Sleep experts say that teens should get about 9 hrs of sleep, so a teen sleeping less than 7 hrs per night is significantly deprived. 57% more teens were sleep deprived in 2015 than in 1991. In just 3 years between 2012-15, 22% more teens failed to get 7 hrs of sleep.

New-media use is both the most strongly related to sleep deprivation and the only activity that increased significantly between 2012-15. Thus smartphones appear to be the primary cause of the recent increase in sleep deprivation, which means this new technology has adversely affected physical and mental health.

Depression

The National Survey on Drug Use and Health of US teens aged 12-17 showed that 56% more teens experienced a major depressive episode in 2015 than in 2010 and 60% more teens experienced severe impairment.  1 in 5 teen girls had experienced a major depressive episode in the last year.

Suicide

46% more 15-19 year olds committed suicide in 2015 compared to 2007, and 2.5 times more 12-14 year olds killed themselves.

Anxiety

Experiments that randomly assign people to experience more or less screen time and those that track behavior over time have both found that more screen time causes more anxiety, depression, loneliness and less emotional connection. It seems clear that at least some of the sudden and large increase in depression has been caused by teens spending more time with screens.