To turn a blind eye is to pretend not to notice something wrong. Turn a blind eye to it, they turned a blind eye, no more turning a blind eye.
It always takes to, and the pretending is the point, since anybody who can turn a blind eye saw perfectly well. The story about Nelson raising a telescope to his blind eye is often told and probably invented.
1phraseturn a blind eyeTo pretend not to notice something wrong.
“The manager used to turn a blind eye when staff left work early on Fridays.”
turn a blind eye is an ignoring.
Probably from the plain image of looking without seeing; the story about Nelson and his telescope is likely invented.
Proto-Indo-European
*terh₁-
English, today
turn a blind eye
Probably from the idea of a person turning to look at something but not seeing it, as if their eyes are blind. The term is frequently claimed to originate from an incident during the First Battle of Copenhagen on 2 April 1801, when Vice Admiral Horatio Nelson (1758–1805) was ordered by Admiral Hyde Parker (1739–1807) through signal flags to discontinue naval action against a force of the Dano-Norwegian Navy. Nelson, who had been blinded in one eye early in his career, said to his flag captain Thomas Foley (1757–1833), “You know, Foley, I have only one eye—I have a right to be blind sometimes.” He then put his telescope to his blind eye and, remarking “I really do not see the signal,” continued the assault which ended in a British victory. However, this is not the source of the term as the Oxford English Dictionary records uses dating to the 17th and 18th centuries.
Etymology from Wiktionary, CC BY-SA
Practised in Idioms