Ohhhh, that's a bad case of ich. Look in that link Tahoe provided and pick a treatment. I would definitely hypo, copper or Chloroquine phosphate. I've also used Quinine Sulfate, under the name Cryptopro on an Antennata Lionfish with good results. This fish needs to come out for treatment.
Sometimes the first thing you notice with Ich and lions is their eyes become cloudy. Their skin will look all funky as well, because they shed that cuticle layer. When they are ill, they shed it over and over until their scales almost look dry. It's something I don't know how to explain. When they are not feeling well, they tend to look like they are "falling apart" with fins splitting and their filaments withering or falling off.
Your case is very advanced. How long has he not been eating well?
Do you have the means of getting him out to a hospital tank? Have you handled a hospital tank before?