Canon EOS-1D X Mark III EOS-1DX Mark III Advanced User Guide - Page 351

3. Aim the camera at the subject. An AF point is displayed around their eye. To choose an eye to focus on, press the < > button to change the AF point to < >, then use < >. As you use < >, the AF point changes again to < >. You can also tap the screen to choose an eye. If your selected eye is not detected, an eye to focus on is selected automatically. 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 < > button. To switch to [Eye Detection AF: Enable], press the < > button again. 351