My 6 year old Registered Paint Mare Spider White Spot... aka "Belle" went blind 2 springs ago. The vet wasn't sure what caused it exactly, but it was sudden. We think she has maybe about 10% of her vision in one eye... and that's it. It was suggested that I put her down, not becuse of pain (she seems to be fine that way) but because she was going to be a danger to ride. Let me tell you.... this horse is soooo trusting I can take her anywhere and do anything with her. The last 2 summers I have gamed her lightly at our local show in Russell Ontario. And while we don't get the fastest times in the games, this year we did win the Reserve High Point Command! The bonus of a blind horse? She almost never spooks while on the trail, and best of all, we get to have an extra close relationship since she relies on me to cue her for obstacles on the trail. There are some downsides too.... but you take the good with the bad and find the blessing for you both that somehow you ended up together