Having never dealt with a snake with eye damage before, take this with a grain of salt but when you said the eyes seemed sunk in a bit I thought about a severe lack of humidity. Have you tried soaking him in warm water in a sealable plastic container with holes in it? When I got my first ball python I was horrible with his husbandry and his eyes sunk in but after researching I figured out why and it never happened again. Just a thought