You may not be blinking enough. I do this sometimes when playing RTS games. After a while my eyes dry out and it's a mix of pain, blurry vision and halos around

You may not be blinking enough. I do this sometimes when playing RTS games. After a while my eyes dry out and it's a mix of pain, blurry vision and halos around light sources until I can let them rest and return to normal. Eyedrops accelerate the restorative process, and probably would serve as a good preventative too. I suggest first minimizing eye strain by ensuring you have proper background light, and that your screen brightness isn't too high. Beyond that, try and remember to blink. It helps to take a moment every once and a while and just close your eyes for a few seconds. Even better if you just take regular breaks, focusing on something other than your screen for a few minutes. Periodic breaks have benefits that extend far beyond just your eyes.