My sympathies towards you situation.
I've volunteered at an equestrian therapy program for the last four years or so. The horses do have to be bombproof. We play games with the riders, so the horses will have to tolerate balls hitting their legs, butt, etc. We also use rings and foam swords, poles and the such, so they have to be used to poles falling between their ears, rings falling all over them, things being wacked around them. We also take them on short trail rides, so they have to be bombproof on the trail as well.
The program I volunteer for only operates Saturdays and Sundays, and each horse goes out approximately four times each day, just walk and trot. Honestly, my program isn't the ideal place to keep a horse. Especially for a sensitive horse, bouncing kids yanking on their faces is not a good mix, and although they're taken care of, they don't really receive the attention they deserve.
I don't believe blindness alone will keep your horse qualifying as a therapy horse.
I guess the only way to see if your horse will fit there is to go out and make sure it's a place where you want your horse to be. As with any regular barn, some therapy places are better than others.