If your work is too busy, and you do not have enough time to sleep, you can close your eyes, and relieve eyestrain when you answer the phone, or go to toilet. I can also recommend three methods which can help you rest your eyes.
First, let your eyeballs do exercises. If you stare at something for an hour, you can make your eyeballs have some movements to relieve eyestrains. For example, looking up and breathing at the same time, then looking down and breathing, repeat it for three times, finally, do the same movement on the left and right sides.
Second, blinking, blinking can promote the secretion of tears, and make the tears applied on the surface of your eyes, which can keep your eyes moist.
Third, massage around the eyes, you can use your hands to rub and press the area around your eyes, which can contribute to ease your fatigue.
Let your eyes rest regularly can keep your eye heath. Here is a simple way. Hope it will works to you.
You shall first of all let your eyes glaze over that can make your eyes unfocused. To achieve this, you shall stop looking or focus something and stop worrying about your surrounding as much as you can. Besides, you can try to relax your body and indulge yourself in your thoughts.
If you have no too much time to sleep, you should avoid use your eyes continually without rest. Try to have a 5 minutes rest every hour. The most effective way to rest your eyes is to see things 5 meters away from you. In addition, we all know the color of green is helpful to our eyes. So you can go next to the window to see some trees and flowers. That would get your eyes relief and probably increase your work efficiency.