Well, we can say that double vision can be caused by eye strain. 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, it may cause the double vision. If you work too long in front of the computers, your eyes may feel dry and tired. The eye nerves will feel tight. Even the eye blood circulation is not that active. The sudden blood pressure because of the intens work amount may cause the double vision, making you see things in blurry.
Yes, it could be one factor that causes double vision. Diplopia is another name of double vision, which is a visual symptom that could be minor or serious. Double vision is the result of the misalignment of both eyes due to functional problems within the vision system, which is known as binocular diplopia. Eye fatigue is mainly caused by seeing for a prolonged period in a short distance during the day. The double vision could appear if both of your eyes are not balanced using.