If you're using any books or papers while working, you can strain your eyes if you don't locate them properly. If they're too low, your eyes will have to refocus every time you glance at them, leading to eye fatigue. You can also strain your neck by moving it to look down too often. Reference materials should be located above the keyboard and below the computer's monitor. To help do this, use a document holder or a book to prop up materials a few inches and help rest your eyes.