Pop-eye is when you physically see the eye pertruding from the socket as if it will pop out.
But if the eyes are cloudy it is often due to larval worms, cataract or baterial infections, and if the eyes pertrude aswell it indicates that other diseases are present.
I'm not too sure on how you can go about treating it though. A good start would be to remoe it from the tank/pond to keep a clower eye on it and remove risk of others catching it.