Brightness and contrast settings?

So, I’ve got this Dell UltraSharp Monitor, and honestly, I’m a bit stuck. I have no clue what my ideal brightness and contrast settings should actually be—it’s just killing my eyes lately. Yeah, yeah, I wear glasses, I know... don't start. Is there some kind of actual way to test for the perfect balance, or am I just supposed to keep tweaking the knobs until my vision starts blurring? Or, if anyone out there knows a "golden rule" for settings, let me know. Thanks

,...what could possibly go wrong?... there are no fixed rules here; you should simply configure the settings in whatever way feels most intuitive to you, as the matter remains entirely subjective and lighting levels along with contrast ratios vary significantly from one monitor to another.