That looks a bit like fungus growing around the eye? I can't tell for sure since the pic is slightly blurry, but is that white area fuzzy?
If so, I suggest doing a large water change, about 70% and adding Sera ectopur salt
It's just like any salt, and it treats fungus AND parasites without meddling at all with the water quality. It also oxygenates the water slightly.
Just mix it in a cup/small bucket with water from the tank and make sure it's dissolved before poring it into the tank.
Generally, I agree with the previous posters, and I'm sure your fish will be just fine!