Could you perhaps give us a bit more information about your fish? For one thing, what is the size of the aquarium it is in, and how many other fish are in there with it? What are the water conditions? Do you know the ammonia/nitrite/nitrate/pH/temp? Does your fish have any other symptoms? These questions may help us figure out whether there is anything you can do to help your fish.
A very important question that has already been asked is whether it is the actual eye that has burst, or merely the fluid filled sac under the eye. Celestial and telescope goldfish are fancy goldfish who have been selectively bred for their protruding eyes. These fluid filled sacs that push the eyes out are very delicate, and as such fancy goldfish should not be kept in an aquarium with sharp objects. You should also keep them with similar fish, as they have difficulty seeing which will make them less competitive for food, etc.
If the bubble under the eye has burst, it may very well grow back without many problems. In all likelihood, it will grow back to a slightly different size or shape than it was originally, so your goldfish may not "match" anymore. Information about bubble eyed goldfish with burst eye sacs can be found.
A protruding eye can also be a disease symptom, though, so if the goldfish has other disease symptoms or you suspect that this isn't just an injury, you should treat your fish as very sick. Popeye is a fairly common goldfish disease that causes the eyes to protrude due to pressure buildup behind the eye. In severe cases, the eye may actually burst, apparently. It can be caused by poor water conditions, can be indicative of dropsy or fish TB, or can be the result of an internal bacterial infection such as septicemia. In some cases, a direct injury to the eye may have similar symptoms.