Someone asked about stories of endurance horses who were blind in one eye. The barn where I board at (www.desertbredcom), had a horse that did Tevis who was blind in one eye - DB Amiga. She finished in the top 50 they said.
I knew her much later, when she was a lesson horse, she taught me how to ride. I did not notice any problems with her vision and wouldn't have known she was blind in one eye if they had not have told me. Being a dumb newbie rider, I didn't think much of it, so didn't do anything to compensate for it, and didn't notice that she wasn't 'normal' as a result either. I was able to do low jumps with her, and never noticed a problem. She was a great horse - all heart and loved to work.
And since we're on the subject of blind horses, there's a place out west that I read about on equisearch.com, where they rescue blind horses. They have great information on how to care for them and some great 'feel good' stories. If I remember, they even ride a couple and talk about how they do that.