Just noticed this on my LB last night? Is this popeye? It doesn't seem to be protruding much, just discolored. He's eating fine and no change in habits.
Injury probably since it is currently only affecting this one eye. How long has he been like this? He probably needs a round of antibiotics to kick the infection. Can you give it in food? Does he eat well?
I would try a dose of antibiotics in the food. I treated a few fish in display this way with good results. I use the Everything Aquatics Triple Cure flakes. Fish love them actually.