Take breaks in their entirety.
Don't short-change yourself during breaks, especially your lunch hour. You can use an app, such as Break Reminder for Windows and Time Out for Mac, to lock yourself out of your computer for 60 minutes. Or launch a simple clock or timer on the screen when you take a break. Rather than just opening YouTube or a social media site, give your eyes a rest and use your breaks to get away from your desk. If you return after only 40 minutes, walk away for another 20.