the reason for such a problem is simply eye strain.
avoid long duration seeing laptop screen, take a break often. wash your eyes often with clean water.
actually this happens because normally there is a tear film covering the eye, long duration staring causes the tear film to dry therefore your eye feels irritation and you need to blink a lot for the tear film to form again.
apart from the above advise, you could use tear drop preparations that are available, out one drop in both eyes and close your eyes and relax for 5 mins. it will help you a lot.