Swollen facial tissue around your dog's eyes is usually very noticeable and can be quite startling. Most of the reasons for swollen facial tissue around the eyes can appear alarmingly fast. Some potential reasons for inflammation include allergies, injury, conjunctivitis, a condition called "cherry eye" and even cancer.
Conjunctivitis is one of the more common reasons for mild to moderate swelling very near your dog's eyes. Conjunctivitis, by definition, is inflammation of the conjunctiva, which is the pink tissue around your dog's eyes. Conjunctivitis in dogs, unlike people, is usually not contagious because it is typically allergic in nature. Signs that it may be a problem requiring treatment include squinting, pawing or rubbing the eyes and yellow or green discharge.
An acute, or sudden, allergic reaction to an allergen like a wasp or bee sting or a vaccine can cause marked swelling very suddenly around your dog's eyes and can include his entire face. This is different than swelling from conjunctivitis, although the conjunctiva is affected as well, because it is more sudden and more severe. As alarming as it is to see your dog looking like a prize fighter that just lost a fight pretty badly, the swelling is treatable. This will usually require a quick trip to your veterinarian for injectable antihistamines and steroids, monitoring and supportive care.
A cherry eye, by definition, is a prolapsed third eyelid gland. Its job is to produce tears to lubricate your dog's eye. The third eyelid gland ideally lives unseen under your dog's lower eyelid. If it "pops out," it appears at the inside corner of the eye as a pink or red little mass about the size of a small cherry, hence its nickname. It is more common in certain breeds such as English bulldogs and great Danes. Occasionally, topical steroid ointment and manual reduction, by your veterinarian, will help to decrease inflammation and return it to its proper hiding place. Often surgery is needed to tuck it back into place.
A good solid whack to your dog's face can easily cause facial swelling, just like it would if it happened to you. So an injury should always be considered as a cause for facial swelling around your dog's eyes, especially if the swelling is asymmetrical -- worse on one side than the other.
One last, thankfully uncommon, reason for swollen facial tissue around your dog's eyes is cancer. Just like people, dog's tend to get cancer just about anywhere. This type of swelling would more than likely be asymmetrical as well. Also, just like with people, cancer can be benign, malignant and everything in between, so a trip to your veterinarian and a biopsy and/or removal will let you know just how much to worry about this type of swelling.