I have one that went blind suddenly about a year ago. He has adjusted very well, but it's been a tough road. When I am leading him to and from the pasture, I always keep a bit of tension on the lead rope. I don't do this with my others, but with him it's important because he needs to know you are there guiding him. You have to watch footing for both yourself and him. You can't let your attention wander when you are handling him. I use key words when the ground is going to change. At first he would stumble a lot, but now he picks his footing very carefully when I cue him. I have even gotten to the point that I can ride my boy again, but that is a whole other thing not to be worried about at first.
Remember he will bump into everything, and things that were never a problem before can be now, even a corner post or a bucket in a stall can be dangerous until he learns how to handle it. You can't pad or clear out everything, just do the best you can. As far as turnout, he will do best if he has a calm pasture mate, that doesn't mind being bumped into or accidentally run over. Mine is fortunate enough to have two, so if I need to pull one of them, he isn't alone. Try not to move anything he is accustomed to, like his water source, and have a particular place you give hay, if you feed hay outside, so he will be able to find things easily. And more than likely, he will be very stressed out for a while, so don't be surprised if he drops weight. Once he gets his other senses working for him better, and begins to feel secure in his environment that will improve, but watch him closely so that you can do what you need not to let him get in bad shape during the process.
And this is the hard part to think about. Not all horses can make this transition when it's sudden like this. Some will also hurt themselves pretty badly just trying to get around. Hope for the best, do everything you can for him, but prepare yourself just in case something goes wrong. Best of luck! Glad you aren't giving up on him!
"Keep a leg on each side and your mind in the middle"