How to perform this exercise:

Imagine a huge clock right in front of you.
Look up at the hour 12 on this imaginary clock;
that would be the highest point your eyes can see.
Then look at the center of the clock (straight forward).
Now look at 1 o’clock, and then again back to the center.
Keep doing that until you finish a full circle (looking back at 12 o’clock).
Repeat the exercise counter clockwise.