You are having a perfect setup for your goldfish & you need not worry about your lionhead if he has developed some sort of extra bubble or sack in front of his eye.They are not a goldfish health problem.The sacks occur because of genetics. Not because of a goldfish disease. your lionhead must be a cross of "Bubble eye"(a type of goldfish).

You just enjoy watching your lionhead evolve into a new fish....

NOTE:The bubble under the eye should not be confused with "pop eye" where the eyeball of the goldfish protrudes from the head. Pop Eye is a serious goldfish disease caused by a bacterial infection and must be treated with antibiotics at once.

sometimes feeding too much protein can cause extra wen growth in orandas, so I could see that happening in other "bubbly" goldfish too. Do you give him veggies?

If it's not inhibiting his vision, don't worry, as long as his water is of good quality (your set-up sounds great!)it should be fine. If it does overgrow his eye's so he can't see, you can remove it. You can use clove oil or MS-222 to knock him out, carefully remove the growth, then place him in a quarantine tank with clean water and some melafix to prevent infection. ONly do that if he's having trouble seeing his food etc. though.

Thanks so much for your help. It's good to know that its not anything serious. I'll try feeding more veggies and less protein and see what happens with the fish.
Thanks again