A retina was a part of human and Time Lord eye.
Unlike a human one, the Time Lord retina was capable of thinking on its own. (PROSE: Seeing I)
Time Lord doors used technology based on retina scans. During the Etra Prime incident, Daleks who found their firepower to be ineffective removed the eyes of a Gallifreyan soldier to bypass the door. (AUDIO: The Apocalypse Element)
Ryan Sinclair explained his absence to his friends with detached retina. Tibo said that sounded painful. (TV: Spyfall)
Retinal ID decoders were used by MI6 operatives in the 21st century. (TV: Spyfall)