Contrast does not cause fatigue or eye strain. Brightness does. If your monitor is hurting your eyes, turn it down. Don’t rely on a designer to use gray text so that it doesn’t hurt your eyes, adjust the brightness directly to the level that is comfortable for you.
Eye strain has many causes - brightness plays a role among other factors as described. If a design requires users to tweak their monitor to feel okay, it's not a good design.
