Horses have the largest eyes of any land mammal and have excelent daytime eyesight. However, having been around ranch working horses most of my life, I've noticed that often, a well behaved horse may balk at entering a darkned barn from bright sunlight. Our well respected veterinarian tells me that they have some difficulty in adjusting to darkness from bright light and they also don't have as good as night vision as humans...Added to this is the fact that horses don't see colors as well as we do and are somewhat skittish about sudden changes in directions on occasion. We do see the horses grazing late in the evening though, so there is some night vision obviously. My Dad had an excellent stock horse that went blind at about 8 years of age. He continued to use the horse, in many familiar areas, until the horse died at age 18. My first horse was a Welsh pony... a gift from my grandfather. She was blind in one eye and I had to be on guard for the times something startled her from the blind side, since she would shy away from sudden noises...