Pescado,
If it is an air bubble (looks sort of silvery, and the eye isn't inflamed) then there are likely two options: mechanical trauma or acute supersaturation of air in the water. The latter almost always shows up with bilateral symmetry - involving both eyes, and there are often other symptoms such as bubbles in the fins, labored breathing, and most fish would be affected.
The first option - mechanical trauma is commonly seen in snappers, grunts, etc. - flighty fish with large eyes. It is also very common in Pristigenys (bigeyes). There is no treatment that I know of for large fish. Small fish can be recompressed in a special chamber (the 2008 issue of drum and croaker has an article about that). Medium sized fish can be captured and the air removed by aspiration (often does not work). But with large fish - the physical act of capturing them makes the problem worse (head shaking in a net, hitting the tank side, etc.).
Can you post a picture?
Jay
