I am so so sorry. As a person who has two Blind horses presently, both aged horses, (and they do great) I know how you feel.
I had a lovely black tovero colt born out of a appy mare, and frame stallion this year.
At first, when he knocked around, I thought maybe he would get some sight after a few days. After the vet came out and confirmed my worst fears, I decided I would give him a shot and see if he could cope. He kept running into the concrete blocks, and into the gates in his stall. I could never turn him out in a stall bigger than 12 x 12. When noises happened, he immediately ran into things. His eyes were there but mishapen, and he kept his head tilted at all times. The mare tried to keep him close but whenever he got just a few feet from her, he would damage himself. I just couldnt see a quality life for him.
After a week, I made the difficult decision to put him down. He was definately not coping with his blindness. I think the reason my older horses are doing so well, is that they both had eyesight for years.
I wish you the best.