When I was breeding appaloosas (years ago) I had a gorgeous peace ck leopard stud-which we discovered, as a 3 year old was blind in one eye-and I knew he had a 1/2 sister that also had sight problems (much more severe). I told the sire owner-who adamantly denied it-but by the age of 17 he was almost completely blind and has also sired a couple more sight-hindered foals.
Then I happened across other colt-black blanketed-totally different lines-and he was blind in one eye.
I'm not sure of which lines are more prone to it-or if that is even the case.
There seems to be a lack of consensus on this one and if some one has a conclusive evidence for a genetic link, I would appreciate knowing it.
It's very touchy blaming certain bloodlines or even a breed.
Blindness is caused by several factors from poor nutrition, lepton infections or by parasites. I raise apps and have wondered about this but have no
evidence for a genetic link. I have one night-blind filly and an old time appaloosa’s man told I...that was because of her blue-specked eye.
I will only reveal her bloodline to private messages.
There is a study going on currently on this very subject. Hopefully there will be a paper out in a year or so (academic wheels grind very slowly).

There IS a genetic eye problem in Apps but I don't know how common it is because you have it lumped in with non-genetic components (eye cancers, parasites, etc.)
I'm afraid I can't help you. I've owned Appaloosas since 1973, and I've never had one with moon blindness. Years ago I had a mare with squalors cell carcinoma in one eye. Also a mare that was night blind, but she was a solid non-characteristic. I have a horse now that's blind in one eye, but that was from an accident as a foal.

Few-spots do tend to have impaired night vision, but it isn't moon blindness.