I'm sorry you're going through this.
PLEASE PLEASE PLEASE DO NOT ACCEPT THIS ANSWER.
It sounds very similar to liver shunt and I would accept nothing short of a bile acid test.
Honestly, I would take him to another vet.
Those are neurologic symptoms if he can jump sometimes.
Walking sideways really has not much to do with blindness.
He NEEDS to be bile acid tested and if there is a liver problem, there is hope.
If the bile acid test is normal, then you could go to a specialist...