In P.D.Q Bach's opera/oratorio Oedipus Tex, after Oedipus puts both his eyes out, "he kind of wished he hadn't."
In Shakespeare's King Lear, the Duke of Gloucester has his eyes gouged out and notably, this is the last Shakespeare-inspired murder attempted by Vincent Price's Large HamSerial Killer in Theatre of Blood, because of the added squick value.
Out, Vile Jelly!
In some interpretations, Cornwall gouges out Gloucester's eyes, and then, for good measure, stomps on them. Squash.
Equus revolves around the events leading up to and following a teenage boy stabbing out the eyes of six horses with a hoof pick. And this is not the Squickiest moment in the play.
Sarah Kane's Blasted includes the sucking out of Ian's eyes from their sockets by a soldier.
Jerome McDonough's play Addict has its share of horrifying moments, but one of the worst is when Janis Evans, under the influence of PCP, hallucinates that there are rats chewing behind her eyes and gouges them out with her grandmother's knitting needles.