In all of Brandons books there are different methods to accessing the magic. there usually seems to be three. I would say that the radiants as a whole would counts a 1 way in general. even tho they have different powers. Then you have Seths way, whatever that is. then you have another way possibly shallans offering?
Anyway I think the eyes MUST be of great importance. Notice that almost none seem to be exactly the same.