There are breeds of goldfish that are characterized by bulging eyes. However, for other breeds, if the eyes on a goldfish are protruding, it may be that the fish has an infection, is physically injured or has a metabolic disorder or that the eyes are responding to poor water conditions.
The Black Moor, Bubble Eye, Celestial Eye and Panda Moor goldfish all exhibit the bug-eyed appearance. This is not a deformation, but rather just a characteristic of the breed of fish. If a goldfish is displaying pop-eye, and it is not one of the aforementioned breeds, then there may be something wrong with the fish or its environment. Diagnose pop-eye by first checking to see if it is present in both eyes of the fish. Bulging in one eye and not the other could be a symptom of a physical injury. Next, notice if the eye is cloudy or bloodshot. This may be due to an infection or parasite.