Davros's ocular system

This artificial eye was a blue lens which was embedded into Davros' 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) It was built by Davros when he refashioned himself to use fear as a means of commanding respect. (PROSE: Davros Genesis)

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 "scratch [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)

Behind the scenes

 * Throughout all of its appearances, Davros' artificial eye demonstrated differing volumes of light emitted from it as well as changing visibility of it from outside. This is due to changes made throughout Doctor Who-history.
 * An anatomy of Davros published in Terry Nation's Dalek Annual 1978 identifies his artificial eye as the "super optic".