To whomever mentioned a CB doesn't key off the WR's eyes is just so far off I can't really fully put it inot words. I played CB at a D-IAA college and we were taught to key off several things depending on the coverage.
The WR can give keys on how he sets up at the line, hands, head movements, etc. You try to get a routine.
A WR when in route can give keys such as if he comes out the same way every time of if he comes real hard on pass patterns that are a certain way than others.
Once a WR is in his break you can see the hips drop and drive as he makes a cut, if he drops his hips lower at times than others you can key on that as well.
Once you are turning and running with a WR you wait for him to turn and make a move for the ball before you turn to locate the ball, if you turn to early you'll lose your man. The eyes are not as important as the arms are, but they are a huge key of when to turn and look.
The only time you use the QB's eyes are in zone coverage, something Fletch has been very good at, I think when he leaves our team and goes somewhere that plays alot of zone, he'll flourish.
A CB has to do so many things right, and as someone stated, a good WR will get open eventually on any CB, they know where they're going and you don't it's so hard.
I marvel at the things even the worst NFL corners can do, because I've been there and I know how tough their job really is.