Thanks all
Lots to unpack here, but I’ll make a start.
It’s very hard for recent ottbs to canter in circles. They lack the balance and muscle to do it. So it’s likely he is not physically able to. Do not chase him or whip him into it.
Is the vet who looked at him a lameness vet? If not, you need to find one. Then find a horse trainer to work with this horse.
If he is having fits walking forward with a rider off a lunge line, he’s either scared to death or he’s got something very physically wrong with him causing pain.
Stop using a whip. Thoroughbreds acting out when you use a crop are liable to do something explosive like flip over and hurt themselves and you. And it’s obviously not working, so that is not your answer.
At a minimum, stop worrying about trying to get him to canter, and start trying to get him to walk in a straight line. No whips. Lots of pats.
But please get a lameness vet and a horse trainer.
How long has the eye been gone?
Could he still be adapting to that?
From your description, it sounds like he’s depending on a person on the ground/at the end of the longeline to figure out his boundaries.
Horse has zero trust in y’all. Get a good lameness exam, check your saddle fit.
Then go watch some of Warwick Schillers relationship videos and build some trust with the one eyed guy. He sounds terrified and herd bound.