I used to ride a big QH gelding in his 20s. When I met him, he had a cataract in one of his eyes. Over the years it became foggier and foggier, then slowly started turning in. His face also sunk in on just the one side, over the entire area, but without pain. It looked like this at the end:
The other eye was basically unharmed.
The horse saw a lot of vets, but it was never really totally figured out. I believe they kind of figured that he had a tumor behind his eye, but it didn't seem to cause him any kind of pain. I believe he could see a little bit out of it, but just the smallest bit. It seemed to be worsened by sunlight, so he wore a modified flymask at all times which had an added dark material over that eye to block out extra sun.
It turned out that they could take the eye out and look around, but since he was in his later years and didn't seem in pain the owner decided to let him be.
I'm curious to know if anyone else has ever encountered a situation like his and if they figured out what was happening in there. This old guy was extremely dear to me and I'd still like to know more about what happened.
Thanks so much