Sometimes one eye is stronger than the other and can see a lot better. As a result you use the stronger eye more often and the other eye can become lazy (often called lazy eye). Unfortunately because the 2 eyes are not being used together correctly, it can make your eyes tired. In addition, you will need to reread the material, and get headaches etc. This condition is called anisometropia.
When reading or working on the computer, do you: