Our 8 yr old warm blood mare is losing hair on her eyelids, around the eye area and on her face.. What could be causing this?

So many things. It could be allergies, it could be insect bites, stress, infection.

You really need to get this treated by a vet, no one on the internet can give you a diagnosis.

It could be parasites(kind of like mange). You should get a skin scrapping and see for sure... I did hear of a horse that lost all its hair because it was allergic to grass. Its still alive,as far as I know...