in regione caecorum rex est luscus
Credited to Desiderius Erasmus’s Adagia (1500).
in the land of the blind, the one-eyed is king
Allowing a single watchman to observe (-optic) all (pan-) inmates of an institution, without them being able to tell whether they are being watched or not. Although it is physically impossible for the single watchman to observe all cells at once, the fact that the inmates cannot know when they are being watched means that all inmates act as though they are watched at all times; effectively controlling their own behavior constantly.
We live in a panoptic society where CCTV’s one eye is the watchman
The name is also a reference to Panoptes from Greek mythology; he was a giant with a hundred eyes and thus was known to be a very effective watchman