Emma and Rylie have them
Emma's had them since she was a young puppy, and Rylie's are somewhat recent (past year or so).
They're all on a raw diet, and drink bottled/filtered water. I know they're from allergies, as they'll go away during low allergy months... but then they'll come back.
I just started them on Angel Eyes Natural 4 days ago, so I'll let you know how that works out. It's supposed to take at least a couple of weeks for results.
http://www.angelseyesnatural.com/details.htm
I wash their eyes daily with a warm, wet cloth, and it doesn't do anything for the stains.
I've heard of people using tums or apple cider vinegar to try to change their ph levels, but I'm not sure of how well they work.
If the Angel Eyes Natural doesn't work, my next plan is to order Eye Envy- it's topical.
http://www.eyeenvy.com/