for having a half blindhorse who then went completely blind ... there really is not a whole lot to do besides enjoying what little they can do without freaking. If your horse now has any bad issues I would say the best thing to do is work and focus on groundwork... a blind horse with issues in groundmanners is dangerous.
I have been teaching my guy tricks (kind of) so that when he lost his sight he would still be able to do things. These are just some of the stuff I did before my guy went blind
taught him to pick up his feet with a tap of a crop. Eventually worked it out so that the height of the tap was how high he needed to step.
Taught him to ride and focus on cues in a hackamore and halter so he wouldn't be unsure with a bit
Worked on densentizing him to shadows and loud noises on his blind side... you need to be ready for freakouts and try to get him to stay calm and trust you... this alone is really hard but if done right it really is a savior.
Make sure he lets you handle his blind side. He needs to be able to relax to thngs he can't see but can feel...
Your voice will be both your best friends so I would really work on voice commands for walk, trot, step, back, side, stop etc...
Ummm... another thing my mom told me that helped was to keep in mind : being half blind doesn't mean you lose the fun, just means you need to find other ways to have fun...
I still can ride my fully blind twh on the trail and we have our cases of freakouts but 90% of the time he is dream just like he was with his eye sight.