Davros' eye

Davros' eye was a blue lens which was embedded into his forehead to replace his lost vision, allowing him a semblance of sight. This appendage mirrored the look of a Dalek's eyestalk lens. (TV: Genesis of the Daleks)

Davros later demonstrated the ability to project electric shocks from his eye. (TV: Revelation of the Daleks)

Jealous at hearing the Twelfth Doctor refer to Davros as his archenemy, commented that she would "claw [Davros'] eye out." (TV: The Magician's Apprentice)

While tricking the Doctor into using his regeneration energy to create a new Time Lord-Dalek race, it was revealed that while Davros did not use his real eyes and had not in a long time, he was not blind and could still open his eyes and see. When he did this, he shut down his artificial eye in the middle of his forehead. (TV: The Witch's Familiar)

Davros' artificial eye was evidently connected to his nervous system and susceptible to pain, as he visibly winced when jabbed him in that eye. (TV: The Witch's Familiar)