Found some things on staining etc I have added a few points here
"Inflammation of the Eyelid(s) (Blepharitis)
An inflamed eyelid is usually the result of blepharitis. This is an infection of the eyelid's edges, which become sore, red and encrusted with scaly skin. Signs may include a thick discharge from the eye(s); spasm of eyelid muscle, especially when exposed to light; swelling and hardening of the eyelid; abcesses; scales and crust; inflammation of the inner surface of the eyelid (conjunctivitis) and loss of skin due to scratching or rubbing (excoriation).
Causes include
Allergies to drugs, soaps, shampoos, and food.
Insect bites or flea bites.
Cat claw injury.
Chemical burns
Parasitic infections such as dermatophytosis, demodicosis (dogs and cats), and sarcoptic mange (dogs).
Chronic inflammatory conditions such as systemic lupus erythematosus (SLE)
Dermatitis caused by nutritional imbalances, including zinc deficiency (Siberian huskies, Alaskan malamutes, puppies) and fatty acid deficiency.
Endocrine system disorders (hypothyroidism and hyperadrenocorticism in dogs) can contribute to the development of chronic blepharitis.
Congenital eye abnormalities such as entropion (when the margins of the eyelids begin to turn inward), lagophthalmos (the inability to close, or poor closure, of the upper eyelid), trichiasis (when the eye lashes are misdirected toward the eye ball and scratch its surface) can contribute to the development of blepharitis."
more details about other issue staining etc can be seen @ http://www.gopetsamerica.com/dog-health/eye-problems.aspx
Some more info
Tear stains, how to keep them clean.
Many pet owners wonder why dogs have watery eyes which causes staining on the hair below their eyes. This condition has a name, it’s called Epiphora. When the hair is wet from excess tearing it becomes a breeding ground for yeast and bacteria to grow. Not only is it unattractive but may be very irritating for the pet. The discoloration may also produce an odor. Tear staining can be traced to health and diet, as well as genetics. Here are some useful tips to help your pet stay "stain free".
Make sure your are keeping your pet healthy: Have your pet examined twice a year by your veterinarian. Watch for ear infections, gum problems, yeast or bacterial infections of the eye (especially Red Yeast) and for stopped up tear ducts - (your pet will show signs of dry eyes).
Pet’s Diet: What is he eating? If you see the words “Artificial, Food Additives and Preservatives“ in your pet food, that is most likely the problem. Cereals such as wheat can cause allergies in both cats and dogs which will and can cause tearing. Minerals in some water can also increase tear staining. If this is the cause, you can which your pet to bottled or filtered water and be sure to use a stainless steel bowl.
Keep your Pet’s Eyes Clean: Hair in the eyes will cause irritations and it feels very bad and will make the eye tear. Eyelashes can grow at abnormal angles and poke the eye, so ask your groomer to trim up that area.
Wash your pet’s face frequently if he is prone to getting dirty. Comb out the hair when it is wet and slippery to remove eye matter. Keep the shampoo out of their eyes to avoid irritation and if you do get soap in the eyes, rinse with clean water immediately.