Canon EOS-1D X Mark III Advanced User's Manual page 351

4.
Take the picture.
Caution
Subject eyes may not be detected correctly, depending on the subject and shooting
conditions.
Note
To switch to [Eye Detection AF: Disable] without using menu operations, press
the < > button and then the <
Enable], press the <
> button. To switch to [Eye Detection AF:
> button again.
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