8 years at max brightness is a long time. You probably have some permanent eye strain damage from that, even if it doesn't feel like it now. The 30% setting was a good call for most people, but monitor age and model matter too. Older LCD panels actually need more brightness to look decent, while newer ones can be way too bright at default settings. I'd also check your room's ambient lighting, because that makes a bigger difference than people think.
Bet your eyes are basically veterans at this point, seen more bright screens than a lighthouse operator. Might be time to give them a 401k and let them retire to a nice dim room.