I've read that it's from being droned with a vril that takes on the identity of host person. The vril enters around the eye and attaches to retna nerve. Extremely painful I read, the drone vril now has the consciousness of the host but that person is essentially dead, no more thoughts of their own, the vril is now in control but has all the past experiences of the host as well as its own now. Problem with that is the while eye wouldn't look like it was punched with a fist.