I have a horse with one blue eye. I've been working her in the round pen and she seems to have huge issues when her blue eye is toward the fence. She'll do anything I want when her blue eye is inside, but we have huge battles when she's facing outward with the blue eye. She's very one-sided, and I'm working on that and she's getting much better, but could her blue eye have something to do with it?

Hey!

I personally would doubt it. I've had several one and two blue-eyed horses before that have no vision problems. I have however had MANY horses that are one sided, and alot of times will have a horse that prefers going one direction in the roundpen than the other. (which I use for training, and not exercising- some of the English crowd seem to get that mixed up at times)

Something else might be that he/she is spooking at something when going that direction. Try using a lunge line, and teaching the walk and trot voice commands; maybe just walk that direction for awhile until your horse gains more confidence going that way.

Hold her facing you and wave your hand suddenly by each eye (not violently of course, but enough to get a blink, or flinch), one at a time and see if you get the same reaction from both eyes,

You can always have her eyes checked out by a good horse vet if you do still think it is the eye.

Horses are dominate sided just like humans, so I'd consider that first. Then check you, are you doing something different in that direction. Ex. Stand opposite shoulder 1 way and more towards her hip the other. Walk around the pen, see what she see's, it will be a different view. Maybe she can see her pasturemates one way and not the other. Work her somewhere else and see if you have the same problems.
As for the coloring, had one- sold last year, part blue and after a vision test he was impaired but after initially breaking out slightly different, treated and rode/competed the same as any other horse. He Evented @ 3'3" and went up to second level Dressage while I had him. Currently have a QH in Reining training, who also has the front blue and wants to be extremely one sided, although as of 6 months ago eye tested fine.
You may be able to figure it out, or just work around it.

Lil Bit has 1 blue eye, but she isn't one sided at all. She does whatever you want whichever side she is on or you are on. Maybe it has something to do with the horse?

Forgot to mention, I heard from a friend the other day that thinks they are more sensitive to bright sunlight than other horses. I have never heard of this and don't know it to be true, but...another idea I suppose. Some fair-eyed people I know are sensitive to the full sun.

I've also heard that blue eyed horses are sensitive to sunlight, but that could very well be another one of those myths. I agree w/AQHA &Ltc4h. Every horse I've ever worked has been more flexible and willing to work on one side over the other. Some are worse than others, but they all do the same to some extent. I just make sure that everything I do to one side I do the exact same to the other side. If I flex to the right, I flex to the left. Disengage, desensitize, everything.