I know I'll probably get flamed for suggesting this, but I've done this with both my cav and my grey with great success...I really like the laboratory food panel.
It is basically bloodwork to determine what your dog is allergic to (foodwise), and recommendation on what to feed.
My poor old grey was allergic to so much stuff, and when I cut it out of her diet, she did perfectly.
My little cav is allergic to less, but sadly I was feeding him a kibble that had one of the allergens, I swapped him to Orijen and he's doing great. It doesn't have the protein source that was bothering him. His ears and eyes look great.