ok in all seriousness now, I would think that it has to do with being underfed.
If you can get the fish to eat I would think that this would fix itself over time, unless it is a deformation that has happened to the fish due to being somewhat stunted. I tend to agree that it has to do with a fatty tissue around the eyes. Seeings how plecs eat i would think a malnourished plec implodes somewhat. Hope you can get your fish to recover, sorry I dont have any thing other than my thoughts to contribute.