my comment was cut off because of too many characters.......see my comment below, and google this if you have this problem--our horse's eyesight saved throught treatment, and many others!!  Google Bill Brown, veterinarian, or Western Montana Equine, Missoula Montana for more info, this is a disease that, if diagnosed correctly, can be stopped in it's tracks, as happened with ours......unable to finish my former comment, but please check it out, if it helps one horse I will be happy!!