Understanding How Horses See
Conditions that would leave us groping for the light switch or flashlight are less worrisome for a horse.
If you've ever walked into the barn at night and flipped the light on suddenly, you'll probably have noticed that the horses blink for quite a long time afterward. This is because it takes longer for them to adjust to rapidly changing light levels. This may also explain why some horses are hesitant to enter dark trailers where they have to go from the bright sunlight to a shadowy trailer. The sudden changes in light levels gives less time for their eyes to adjust.
Spatial Perception As prey animals, horses' vision played an essential role in being able to see predators and take flight before they ended up as dinner. Eyes set on the side of their heads–rather than on the front like ours–enable the horse to have almost 360-degree vision. They are unable to see a short distance directly in front of them and directly behind them,
which is why one of the safety rules for working with horses is to speak to them when moving behind them. Since a horse has difficulty seeing things directly in front of them, when they are negotiating jumps, a narrow bridge, or other obstacles, they may briefly be doing it while effectively blind. However, because the retinas of their eyes are very large, horses have very good peripheral vision. A subtle turn of the head allows a horse to focus in on an object.
Horses may see into the distance better than we do. It's also likely that they can see motion with greater sensitivity than we can, which is very important for spotting predators before they become a real threat. Horses also seem to be able to see things in more detail than many other animals.
Eye Color
Horses may have brown or blue eyes, with brown eyes being far more common. Appaloosas, Paints, Pintos, and other horses with lots of white on their faces will sometimes have blue eyes. There's no difference in the vision of these horses, although some people may feel they look more likely to spook.
