the round ball that forms the whole of your eye, including the part inside your head
if two people are eyeball to eyeball, they are directly facing each other, especially in an angry or threatening way
if someone is up to their eyeballs in something, they have more than they can deal with:
She's up to her eyeballs in debt.
if someone is drugged up to the eyeballs, they have taken a lot of drugs so that their behaviour is severely affected