Diamond eye is hyper-pigmentation that may spread to cover the eye over time. This is a disqualifying trait in betta shows and not something you want to breed to continue. I have spoken to a few breeders and they say that the betta should still be able to "see" even if the entire eye is covered. Some breeders will try to sell this type of fish as a "rare" and expensive fish but we do not fully know how the fish is affected ..and therefore I do not think it is fair to sell a show flaw for a higher price.

Diamond Eye Metallic Plakat Male