Blind boy will be ten times harder than training a full sighted horse, just be prepared for that.
My good friend rescued a very big ex racehorse with degenerative cataracts in one eye. That horse tried his heart out for his handlers- was a really sweet gelding and even so he took so much more time to retrain due to the blindness. He'd almost act ashamed after spooking (usually after being directed to the left, same as his bad eye) it took years of consistent, clear handling and work to get him calmly going in both directions in different sorts of circumstances.
Just stay safe and don't be afraid to ask for help from your trainer.