The orbit is the bony cavity that contains the eyeball and all of its associated muscles, vessels, and nerves. Inflammation of the orbital area, called orbital cellulitis, is common in large and hunting breeds of dogs and much less common in other breeds. This condition may be caused by foreign objects in the eye (such as a porcupine quill, thorn, or grass awn) or by an infection that spreads from another part of the body. The most common signs are severe pain on opening the mouth, swelling of the eyelid and conjunctiva, extension of the nictitating membrane (the third eyelid, a thin membrane beneath the eyelid that can extend across the eyeball), and “bulging” of the eyeball. Inflammation and swelling of the cornea may develop due to the dog’s inability to close the eyelid fully.
In severe cases, antibiotics given by mouth or injection are usually effective, but if swelling behind the last molar is present, drainage of this area may be required. Warm compresses and topical lubricants such as eyedrops to protect the cornea are often also used to treat these conditions. Relapses may occur, and x-rays and ultrasonography of the adjacent teeth, sinuses, and nasal cavity are often used to check for other factors that might be contributing to the condition.
Also see professional content regarding the orbit The Orbit in Animals The dog in this photograph is showing acute onset of orbital cellulitis. Exophthalmos and elevation of the third eyelid are evident. Clinical signs of orbital cellulitis are acute pain on opening... read more 
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