Red-eye was originally thought to be a disease found amongst enslaved Ood on their homeworld of the Ood Sphere. Its symptoms were bright red eyes, rabid temperament and anti-human sentiment.
It was caused by the subconscious of the Ood Brain reemerging amongst the Ood after 200 years of slavery, due mostly to the sabotage of Ood Operations's systems by the Friends of the Ood. It led to the Revolution of the Ood in 4126 and the freedom of the Ood. (TV: Planet of the Ood)
The Eleventh Doctor once encountered an Ood with red-eye. (COMIC: Take a Bow (Tie))
An Ood with red-eye and a bandaged head appeared on a television advertisement for Lawyers Against Time Lords. (COMIC: No Win, No Fez)