Iris ring

The iris ring was identified by the Dalek Survival Guide as a component of the Dalek eyepiece. (PROSE: Dalek Survival Guide)

History and variance
In what the Time Lords identified as the Daleks' "early period", (PROSE: Dalek Combat Training Manual) the Dalek eyepiece featured a white circle or "iris" as seen on the Skaro City Daleks, (TV: The Daleks) the Dalek Earthforce, (TV: The Dalek Invasion of Earth) and the silver Daleks. (TV: The Chase)

The text of the Dalek Survival Guide claimed that the eye lens "iris" of the Dalek Prime's Emperor Type 2 casing was "solid white", (PROSE: Dalek Survival Guide) but its own illustration and another source concurred that the lens actually had a black "pupil", (PROSE: Dalek Survival Guide, COMIC: Invasion of the Daleks) and one account showed that the lens was blue. (COMIC: Invasion of the Daleks)

The Dalek Prime's immense Emperor Type 3 casing had a solid white iris like his subordinate Black Dalek Leaders and silver Dalek drones, (TV: The Evil of the Daleks) though a variant of this casing existed with a black pupil. (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe)

Later grey Daleks had a circular white iris ring with a dark center, as did the Gold Daleks, (PROSE: Dalek Survival Guide, TV: Day of the Daleks) later Black Supreme Daleks, (TV: Resurrection of the Daleks, Remembrance of the Daleks) modified silver Daleks, (TV: Death to the Daleks) and the Necros Daleks. (TV: Revelation of the Daleks) The black-and-gold Dalek Supreme had an illuminating iris. (TV: Planet of the Daleks) The refined Imperial Daleks had a gold iris ring. (TV: Remembrance of the Daleks)