Understanding How Horses See
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.
