This article talks about the research into sports performance and “quiet eyes.”
“When you do feel anxious, try to control your visual attention, stay visually focused on your target and keep your gaze steady.”
Mostly they’ve studied golfers, but I wonder about its application to climbers. It seems to me, when I am stressed while climbing, I have the opposite problem – I am so focused on what’s right in front of me, that I don’t look around to see other holds. But maybe my eyes are moving so fast, I don’t see additional holds.