For every 20 minutes, take 20 seconds break and look 20 feet away to rest your eyes.
This basically revolves around the idea that you should not keep staring at your monitor for extended periods of time, whether you're working or playing games.
Why not give it a try?
Ergonomics is the scientific discipline concerned with designing according to human needs, and the profession that applies theory, principles, data and methods to design in order to optimize human well-being and overall system performance.  The field is also called human engineering, and human factors.
Catz: take only 20 seconds tau, not 20 minutes ... muhaha