Unfortunately this will only muddy the waters for you, but my vast experience with contact dermatitis has shown that an allergen will usually cause a reaction everywhere that it touches me, but not always.
Years ago when sunscreen still contained PABA, it would cause an itchy rash on my forearms, but nowhere else.
More recently I had a a patch of red, itchy, scaly skin on the browbone and eyelid of my left eye. Only the left eye. Eventually I determined it was caused by the Almay eye makeup remover I was using. And I used it on both eyes, but it only caused a problem around the left one.
So if your problem is contact dermatitis, then it might be caused by something that is not only coming into contact with your eyelids. It might be contacting you elsewhere but only causing a reaction around your eyes.
Now, having said that, since you mentioned pillowcases -- have you tried a different pillow made of different materials than the one you use now? Like maybe switching from poly- or down-fill to memory foam? You can also try to rule out or confirm that the cause is related to your pillow/mattress/etc. by sleeping somewhere else for a few nights, like in a recliner in the living room if you have one and can get comfortable enough.
- Gray 2010 carbon WSD road bike, Rivet Independence saddle
- Red hardtail 26" aluminum mountain bike, Bontrager Evoke WSD saddle
- Royal blue 2018 aluminum gravel bike, Rivet Pearl saddle
Gone but not forgotten:
- Silver 2003 aluminum road bike
- Two awesome worn out Juliana saddles