Protopsis is an emergency medical condition in which an otherwise healthy eye explodes or falls out of the orbital socket that normally contains it. Though it can happen in any breed, it seems to occur most often in those with short and wide faces such as pugs, bulldogs, and pekingnese.
Protopsis can happen for a wide variety of reasons. It could occur as the result of trauma such as a scratch or bite by another animal, even when the resulting damage is not externally visible. Likewise, it could occur as the result of pressure exerted upon the inner eye from the build-up of ocular fluids. It's even possible for protopsis to happen spontaneously with no discernible cause whatsoever. In any of the above cases, however, the likelihood of it happening is compounded by a number of factors such as injuries that force the eyelid to remain open for an extended period of time, a wide and flat skeletal structure whose orbital socket is not well suited for holding in an eye in the first place, or disease which affect the diameter of the eyelid opening, such as macropalpebral fissure syndrome.
Protopsis is very easily diagnosed with even the most cursory of glances, as it should be readily apparent that a dog's eye has become dislocated from its socket.
When protopsis occurs, it must be treated as a medical emergency. Keep the eye clean with a sterile saline solution such as "artificial tears". Cleaning solutions should never be used as they're too caustic and could cause damage to an otherwise salvageable eye. As a last resort, however, clean fresh water can be used. Your dog should not be allowed to partake of any food or water for the duration of the emergency because in addition to the likelihood of introducing foreign bodies to the open socket, it's very probably that your dog will need to be anesthetized in order to replace the eye, and this is best done on an empty stomach. If the eye is saved, a secondary surgery involving lengthening and strengthening of the eyelid might also be necessary.
Even in cases where the eye is returned to the socket successful, follow-up treatments are critical. Depending on the cause of the protopsis and the length of time that the eye remained out of the socket, there is a very significant chance that vision will never be restored to its former clarity. Infection is also a distinct possibility, and in this case the eye will have to be surgically removed as a preventative measure to stop the spread of infection to other parts of the animal's body.
If the event that your dog's eye does need to be removed, this is usually accomplished via two different methods. The first is that the eye is simply removed and the lid is sutured shut, but this can produce an unpleasant looking depression in that part of the face, so many owners opt to have an orbital prosthesis installed in the socket and to have the lid sutured over this so that it simply appears as if the dog has one eye shut. In lids that are prone to infection, however, or in flat-faced animals, prosthetics are generally not advised.