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Just found #2. It's The Manster (1959). It's in the credits in It Came From Hollywood, but omitted from the Wikipedia and IMDB articles.
1 is a novel by Stephen King, called The Dark Half. It's a rather strange story where they cut the main character's absorbed twin out of his brain when he's a child but never tell him or his parents what the tumor really was. But later the twins personality does surface and the main character uses it to write stories under a pseudonym, that he later kills off, even giving it a fake burial for an article in a magazine. Then the pseudonym literally crawls from its grave and starts killing people.
Thanks for the info!
I did a bunch of searches with "Stephen King" and various keywords for the premise I described, but didn't find anything relevant. That's why I figured it probably wasn't him.
Looking for two works that serve as examples for Eyes Do Not Belong There.
1. Someone told me there's a Stephen King novel where surgery reveals an eyeball on the back of someone's brain. It's what's left of his identical twin, whose evil personality later surfaces. I've done some searches and it probably wasn't really by Stephen King.
2. A black and white horror movie where somebody (looks like Lon Chaney, Jr) grows an eyeball on his shoulder. A clip of it is shown in It Came From Hollywood.