Abscesses, hematomas, and tumors in the retrobulbar space behind the eye can push the globe forward and cause bulging.
A retrobulbar abscess (an abscess behind the eyeball) is an extremely painful condition that comes on rapidly. The face around the eye is swollen and the globe is extremely tender to finger pressure. Dogs experience great difficulty opening and closing their mouths. A retrobulbar abscess must be surgically drained.
Retrobulbar hematomas (blood clots behind the eyeball) also develop suddenly. They occur with head injuries and can appear spontaneously in conjunction with some bleeding disorders.
Tumors in the retrobulbar space produce a gradual bulging. Unlike the two conditions just described, they are relatively painless.
Chronic glaucoma can lead to increased eye size and protrusion.