As you have said, you have hard work and after the hard work, your eyes feel tired and strain, even have the double vision. When people work hard for a long time, it is easy to have eye strain because they have to focus their eyes on one thing for a long time. Then, the eye strain will just decrease the blood flow and in this way, your eye will become blurry, and just like we often say, the double vision happen. So in my opinion, you should not work too long, and having a good rest is also beneficial for your eyes.
Yes, the stress may cause the double vision. If you have great stress, the body normal state will be broken. The blood pressure will be increased which may cause the double vision for the eyes. You'd better have a good rest for your eyes and use the eyedrops to prevent the dry eyes.
Sometimes people really seem to be workaholic and don't pay much attention to their health and eyes. I mean, our eyes are integral part of our lives which deserve our care and attention you know? Indeed, working too much will lead to some physical and mental disorders which might weaken your whole body. Eye strain and stress is a common problem, which may give rise to double vision. What you should do is to take enough time off to rest your body and mind.