What do you do if you look at the computer so much that your vision is blurry and your eyes hurt a bit?

Look at it less. While a flippant answer, it's actually the key to preserving eye health. Tiring of the eye muscles can lead to headaches or blurred vision, and the best way to overcome it is to give the eyes a break. Every 45-60 minutes, get away from the screen and walk around, which will also help your heart health. If blurring continues, you may need to see an eye doctor.