The horse's visual capabilities are unique and well suited to its needs. The uniqueness of the horse's vision contributes considerably to the horse's reputation for spooking easily. The horse's eye is not round and, therefore, the retina and cornea are not equidistant from each other across the eye. In order to focus on an object, the horse needs to turn its head and focus with both eyes.

FIGURE 9.7: The Eye of The Horse

Aside from being an animal of prey with a built-in flight response, another contributing factor to the horse's tendency to spook is that the placement of the eyes on either side of the head makes the horse's vision largely monocular. In contrast, humans have binocular vision, which means that both of our eyes see the same image within the brain. But the horse has one view of the world on the right side of the body and a different view on the left side. The brain doesn't blend both images into one. This independent vision allows the horse to be on the lookout for predators while grazing.

Anyone who trains or rides horses needs to be aware of this fact. If the horse spooks at something on the ground, you need to let it walk up to the object, investigate it, and see it from both sides. If the horse hasn't seen it from both sides, the object will only register on one side of the brain.

The horse can see as much as 350 degrees around its body, with a blind spot directly in front and directly behind. Anyone who handles horses needs to be aware of this limitation and, for safety reasons, avoid standing directly in front of or behind a horse. You should also speak quietly to a horse when you approach it from behind to announce your presence and make sure it won't be startled by your sudden appearance within its visual field.