Join Date: Apr 2008
Location: Alberta, Canada
Horses actually remember by scent, not by sight. To horses, we all look the same, but we all smell different. That's how they sense predators in the wild; they don't have to see them, they smell them before.
Once he associates your smell with pleasent things, you'll go a long way.
I'm assuming your rescue knows what they are doing, but blind horses do have to have a very controlled envrioment as they can't see. One of the things I've found best is putting a ring of gravel around any obstacles in the pasture (Ex. if there is a tree, but a ring of gravel (or some other substance but gravel works best) about a foot around, same with the fence line, etc) so that they know when their feet touches that, there is something ahead.
Although he can smell and hear you, I would never walk up behind him and touch him without speaking (you shouldn't do this anyway, but I'm guilty as charged in my own pasture with horses I've known forever - One of these days it's more then possible I could spook one and get a boot for it).
As Endiku said, talking helps him to keep your location and is often very soothing for horses, especially those who can't see.