Dalek eyestalk
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 and also track a person's footsteps. (DW: Destiny of the Daleks)
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 and the Dalek's weapon would be fired in a blind panic, usually accompanied by the frantic screaming of "My vision is impaired— I cannot see!" However, post-Time War Daleks overcame this exploitable weakness. For example, a Dalek was shot in the eyestalk by Wilf with a paintball gun. The paint was immediately melted off and the Dalek was heard to say "My vision is not impaired." (DW: The Stolen Earth)
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)
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)
During the Shoreditch Incident, Ace fired an ATR (Anti-Tank Rocket) at an Imperial Dalek and was shocked at the damage. She responded by saying "I aimed for the eyepiece." While inside a Dalek shuttle craft, the Doctor placed his hat on a Dalek's eyepiece to confuse it.
