blind 13 year old Appaloosa Gelding

My friend has an Lepard Appaloosa Gelding named "Band on the Run" we just call him Oreo, anyways he has always been spunky and nervous of lots of things, making him hard to ride. She had the vet come out about 3 months ago and they told her he was going blind, which is very odd for his age (13) She still rides him , but we both think it is very odd.....
Does anyone here have or know of someone who owns a blind (or going blind) horse?
If you have any questions.. or you want more information about Oreo.. Please ask!

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Horse_1987