Davros's ocular system

Davros had an artificial eye, formally known as an ocular system, embedded into his forehead to replace his lost vision, after the destruction of a Kaled bunker by the Thals during the Thousand Year War rendered him almost completely blind. This appendage mirrored the lens attachment featured on a Dalek's eyestalk, (TV: Genesis of the Daleks) in particular those of the bronze Daleks. (TV: Dalek et al.) 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 artificial eye, which he shared with his decoy. He used this power to disarm Orcini, an assassin hired to kill him. (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 Twelfth Doctor into using his regeneration energy to create a new Time Lord-Dalek race, Davros showed that, although he did not use his real eyes and had not in a long time, he was not entirely 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.

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)

Alternate universes
In one parallel universe, Davros had an ocular system installed in his forehead (AUDIO: Palindrome) near-identical to that of the N-Space Davros following the Last Great Time War, (TV: The Stolen Earth, Journey's End) after the Dalek Time Strategist of N-Space began using this Davros as a focal point to merge echoes of every Davros from across the multiverse into a singular form, in its mission to restore the Daleks of N-Space (AUDIO: Palindrome) after their near-extinction at the hands of the Valeyard during the Last Great Time War. (AUDIO: The War Valeyard)

In the Unbound Universe, Davros had an ocular system installed in his forehead, (AUDIO: Masters of War) near-identical to that of the N-Space Davros between the latter creating the N-Space Daleks (TV: Genesis of the Daleks) and the aftermath of the Last Great Time War, (TV: The Stolen Earth, Journey's End) after he was crippled by an attack from the Quatch during the Quatch Empire's first attempt at conquering the Unbound Universe's Skaro, as the attack rendered him blind. This ocular system, along with Davros himself, was destroyed when, during the Quatchs' second attempt at invading Skaro, Davros used a secret program to deactivate the technology stabilising the Quatch in the Unbound Universe; the resultant vast instability of dozens of Quatch returning to their native dimension destroyed the Quatch mothership, which Davros was onboard at the time, thereby killing him and destroying his ocular system. (AUDIO: Masters of War)

Behind the scenes

 * Throughout all of its appearances, Davros' artificial eye has demonstrated differing volumes of light emitted from it as well as changing visibility of it from outside.
 * An anatomy of Davros published in Terry Nation's Dalek Annual 1978 identifies his artificial eye as the "super optic".