Retina

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)

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)