We stare at our screens, a lot. It's one of the side-effects of living in a technologically advanced world. If you don't take preventative actions, this prolonged screen activity can result in harm to your eyesight.
The American Optometric Association recommends that you take a 20 second break, every 20 minutes, by looking at something 20 feet away.
This is known as the 20/20/20 rule.
The 20/20/20 app ensures that you'll be reminded to take a break every 20 minutes. It is completely free, with no advertisements, forever.