Dalek eyestalk

Dalek eyestalk
Type:	Electronic eye
Place of origin:	Davros, Daleks
Appearances:	All Dalek stories

The eyepiece, also called the eyestick or similar names, was the part of the Dalek which enabled the Kaled mutant inside to see. The eyepiece could magnify images so that the Dalek could see across great distances.

The eyepiece was the most vulnerable part of the Dalek. When it was taken out or covered, the Dalek no longer remained a threat. After the eyepiece is destroyed, its head would spin around uncontrollably.

After the Daleks harnessed background radiation as a power source during the Last Great Time War, they developed a shield for their casings that would melt bullets, making the eyepiece more protected and harder to take out. (DW: The Parting of the Ways)

A Dalek's vision.

To escape from the Dalek base, the Doctor threw his hat onto a Dalek's eyestick and the Dalek began firing and destroying the command center, almost hitting Davros in the process until the Doctor destroyed it.(DW: Destiny of the Daleks)

To escape from Davros' base in Tranquil Repose, the Doctor took out a Dalek's eyepiece and Peri attached a grenade to its casing, destroying the Dalek. (DW: Revelation of the Daleks)

To get inside Dalek spacecraft, Seventh Doctor also put his hat on Dalek's eyepice.