Just as you said, you say you use computer screen too long, this may be the reason why your eyes hurt when you are tired. Seeing the computer screen for a long time is really bad for your eyes. And this may cause your eyes dry and a little pain and your eyes may feel very tired and sleepy. If you have to work in front of the computer for six to eight hours, you are supposed to have a rest for every two or three hours, such as having a cup of coffee, going for a little walk, going to the washroom.
Second, adjusting the brightness of the computer screen, the screen font and digital like the small bulbs which directly hurt your eyes.
Therefore, you need to have a reduction in the screen brightness. What's more, doing eye exercises is also a good choice to give your eyes a rest. If you want to continue your work, you can go to the hospital to have an eye exam and ask for the doctor's advices.
Well, there are many reasons which can make your eyes hurt when you are tired. Now we can have this talk from the organs of eyes, first, you should know that there are six muscles which move the eye to follow what you're watching. There is a muscle for widening and a muscle for narrowing the pupil to control the amount of light received. There are also muscles used to focus the lens of the eye based on the distance we are from the object we are looking at. These muscles are duplicated in the other eye as well. When we are tired, our eyes have been using these muscles and have become tired as well. So if your eyes feel hurt when you are tired, it's normal. At this moment, I think you should not do some work but have a good rest so that your energy can recover.
Your tiredness caused by the long time work before the computers must affect your eyes. The tiredness may make your immune system decline. In addition, long time use of eyes before the computers may make your eyes feel dry. That is real reason for the eyes to feel pain. You should make the time of using eyes less. Having a good rest and using the eye drops can you feel good.
If you work in front of your computer for a long time, eyes don't truly get tired, but oftentimes your tiredness can cause or worsen dry eyes. When we get tired, we often stare off or force our eyes to stay open in an attempt to keep from dozing. This can cause the tears on the eye's surface to evaporate as well as decrease the amount of new tears that blinking would normally put onto the eye. The result is the burning sensation of dry eyes and then your eyes will be hurt. However, according to your description, you can use artificial eye drops to moisture your eyes and relieve fatigue. Moreover, you can have a rest after 45-minute work.