I wouldn't count on the previous owner knowing about it, if she were to have it (Great that you might be able to get some history from him though!!) - like don't not get them checked because he had never noticed anything, you know what I mean? :)
I'm just a bit oversensitive about it because with my girl, she's 100% blind in one eye and has less than 50% vision in the other eye AND NO ONE KNEW (myself included+she was boarded for nearly 2 years under the daily care of a woman with over 40 years horse experience!) until she had a really serious flare up last spring, the vet suggested that ERU might be the cause, then I researched and found out what I know now.
I had had her for nearly 4 years (seeing her daily for most of that time) once she was finally diagnosed and with how bad her vision is now, she has to have had ERU for probably 10 years.
I've never seen her bump into anything, ever, she's not spooky - if anything, she's one of the least spooky horses I've met (once she knows what her surroundings are like - she can be pretty clingy+spooky during the initial "settling-in" phase), I can ride her at all gaits, she happily runs up and down hills+over uneven terrain... It's terrifying for me!
Anyway, I'll get off my soapbox but all I'm trying to get at is that a horse with vision issues does not necessarily act like what "we" expect an animal with vision issues to behave like. I had always thought that blind horses always act blind...turns out they don't necessarily have to! Whooooo knew. Haha!
I don't mean to worry you or anything, it's just a topic very close to my heart!