How Do Horses See Things?
by Elaine Polny
The Equine Eye
Humans and horses literally see things differently, and this difference can sometimes lead to problems on the trail. No doubt you've ridden on windy days when suddenly your horse became agitated and excited. A piece of paper flew across the road or trail and your horse jumped or stopped dead in its tracks. This might well be the same horse you rode on this trail yesterday without a hint of shyness.
This sudden change of behavior was because your horse sees differently than you do. You didn't give a second thought to that piece of paper flying across the trail. Your horse, though, saw a strange, out-of-focus object moving across its path.
The fear of unidentified moving objects comes from being a prey animal. For centuries equines served as tasty meals for big cats and other predators.
Thankfully, Mother Nature did not leave the horse defenseless against predators. She blessed the horse with an unusually broad field of vision, keen hearing, the ability to lash out with front and back hooves and, most importantly, the ability to outdistance all but the fastest of pursuers.The Equine Eye
The equine eye is unique in that it has both monocular and binocular vision. With monocular vision, the horse can see objects with one eye. As a result the brain often is receiving two images at the same time, sort of like a human attempting to watch side-by-side television sets simultaneously and absorb the action on both. With binocular vision, however, the horse can see the same object with both eyes at the same time and only one message is conveyed to the brain. A horse's eyes are wide apart and on each side of its head to accommodate monocular vision better, very important to a prey animal.
Humans have only binocular vision. We fall into the predator rather than the prey category. As such, our eyes are in the front of the head, and only a short distance apart, just like other predators--lions, tigers, dogs, and cats. A predator's eyes are designed to focus on the prey it's attempting to chase down.Auto-Focusing Mechanism
The human eye is a lot like an auto-focus camera, making use of disc-like lenses that are attached to powerful ciliary muscles. These muscles quickly flex or relax to adjust the lens shape as needed. If you want to look at something far away, you simply stare at the object and, in a flash, the lens focuses on it and you see it with clarity. If the object is close, the same thing happens, only the focal point is much nearer.
If you want to look at something to either the right or left, you simply turn your head and the ciliary muscles do the rest, sending a sharp image to the retina, a mass of nerve receptors on your eyeball's back wall. The retina then transmits the image to the brain--all in the proverbial blink of an eye.The horse's ciliary muscles are underdeveloped and do a poor job of bringing objects into focus
. There is also a big difference in the retina. In humans the retina is a smooth, concave surface. The equine retina is more concave in some places than in others, and some sections are nearer the cornea than others. Focusing Problems
Because the horse can not focus on objects as we do, it compensates by lifting and lowering or weaving its head from side to side. It may also try to get either farther away from or closer to an object to bring it into focus.
Even when the horse has focused as best it can, its sight is only three-fifths that of a human. In other words, when looking at an object twenty feet away, the horse sees only as much detail as a person with twenty-twenty vision would if the object were thirty-five feet away.
This means, of course, that when you're riding down the trail and see a strange object ahead, you'll recognize what you're seeing long before your horse does.Monocular Vision
Because a horses eyes are large (the largest of any land mammal) and on each side of its skull, the horse has a very broad field of vision. A horse actually has a vision field of more than 350 degrees, compared to the less than 180 degrees in the human.
Only about 65 degrees of the horse's field of vision are binocular--seen with both eyes--while the remaining 285 degrees are monocular--seen with one eye.
So, the next time your horse is acting differently than expected, take a moment to see with their sight and perspective it will offer much added information to the situation.
Training Horses NaturallyWith thanks, this information was compiled from thehorse.com article#16100 by Les Sellnow.