Cowfish Eye problem

[NEK-ap24]

Hello,
I purchased this little guy a few weeks ago (the kids call him Waylin (because it sounds like a cowboy name)) and at that time he had a small visible white growth on his eye. I was told by the LFS that it was likely just a physical injury to the eye and would heal on its own.

It has since grown, and it appears as if the skin around the eye and up the left horn has sluffed off, yet the spot on the eye remains. I have tried a treatment of Rally (sales add says this: Reef Safe Rally is a copper free water treatment. It can be used in any tropical or marine aquarium with harmful bacteria, flukes, or oodinium Safe for plants and invertebrates.)

with no effect. Here are two current pictures.

Any suggestions would be helpful. I am going to do another water change and then try Furan-2, unless someone suggests otherwise or cautions against it for some reason.

Thank you,

[NEK-ap24]

Okay, no response...so Furan 2 it is.
I thought more folks read this section to help out with problems. Perhaps everyone is stumped? Or is it so obvious that it is painful?

I will update how the Furan 2 treatments go.