The Curious World of 
Horse's Vision

We are learning more about horse's vision all the time. We are able to use the same instruments to compare the anatomy of the horse's eye to the human eye. Carefully controlled experiments are performed to study equine vision and to eliminate possible errors. Horses actually see very similar to the manner that humans see. But there are some important differences between the species.

The horse's eyes are placed on the sides of the head, in common with most open-space herd animals. This permits the horse to view nearly a full circle of visual field. It is believed that a horse can see in a full circle with the exception of immediately behind them or directly in front. It is like a wide angle panoramic view of their world. Dr. Evelyn Hanggi, president of the Equine Research Foundation in Aptos, California explodes the myth that horses see with one eye at a time with no connection between the two. She explains that the myth of no communication between the two eyes would be bizarre in the animal kingdom. She notes that like nearly every other mammal, horses have a structure in the brain called the corpus callosum which connects both hemispheres of the brain, thus sharing information back and forth.

To prove the eye connection theory, Dr. Hanggi established tests using images that the horses had never seen before. No humans were nearby to give inadvertent signals. The horses were given a choice of pictures to touch with their noses and receive food rewards. The horses were trained to respond to one of two choices while one eye was blindfolded. When the blindfold was switched to the other eye, the horses had no trouble selecting the correct image. These results maintained a consistency throughout the entire test series.

Some have observed that a horse will shy at a mailbox when approaching it from an unfamiliar direction. There are many thoughts and answers surrounding this problem. One obvious answer is that horses just do not have the skill to recognize objects when seen from a new angle. The results of Dr. Hanggi's experiments reveal that a horse may recognize a target if it is rotated but may not recognize all orientations. She believes that training may be more of an influence than vision, per se. They need to be encouraged to examine their surroundings in a more careful manner. It is important to note that horses who have been exposed to many objects in different situations and have developed a trust in their riders will tend to react more calmly and efficiently when confronted with a new or unusual stimulation.

Other reasons that a horse may suddenly stop and will shy from an object can range from changes in lighting, contrast and shadows. Also, one must be aware that the horse may be seeing something that you do not. It could be a mouse or a snake in the grass or even a tin can that rests in a different position than it did just one hour ago.

We think nothing of the trail hiker or rider who will look behind and about him to utilize landmarks that may be unrecognizable when returning from an opposite direction. And so the horse, also, may not recognize a potentially scary object on the way home from a different direction, so he needs to investigate the situation all over again to convince himself that what he has just encountered is not a threat to his survival. For instance, if you are crossing a creek for the second time but from the opposite bank for all intents and purposes, that will be a different creek for the horse. If he has crossed this and many other creeks before this it probably wouldn't be a big deal to the horse. But if he is just learning to navigate stream beds, it would be wise to allow him the time to adjust to the new task.

There is the myth that because horses have an eye on each side of the head that depth perception is impossible. It is true that a monocular view of objects does not afford depth perception. Adherents to this viewpoint have some issues with the concept. While true monocular depth perception may not be perfectly achieved there are many other clues that raise the perceptual skills utilized in replacing true depth perception. For instance, the size of the objects, shading and distinctness of the targets and even sound clues are also useful where true stereopsis is lacking. Humans with one eye often become quite proficient in this regard.

More importantly is the knowledge that a horse possesses a 55-65 degree overlap in his vision field which affords him true depth perception in that area of binocularity. Horses have a natural inclination to refine their depth perception by raising, lowering or tilting their head. If a horse is asked to jump, cut or maneuver closely around or through something, he is going to do better with a loose rein and the freedom to move his head to enable him to better judge distances. Dr. Hanggi points out, "Humans tend to have tunnel vision and concentrate only on what is in front instead of being aware of the whole environment."

Dr. Alison Harmon of the University of Western Australia reports that the small blind spot in front of the horse's nose may provide difficulties for some riders during dressage requirements. Horses have been seen cantering around the arena in a freestyle routine and collided head on. Their vision was directed down their noses towards the ground so they simply didn't see each other. Dr. Harmon used an ophthalmoscope to examine the horse's eyes in order to determine the retinal field of vision. She discovered that in a frontal position the visual eyes run approximately down his nose. The blind spot exists in front and slightly above eye level and occupies an area about equal to the horse's width. If a horse is ridden "on the bit" with his forehead vertical to the ground, or "behind the bit" with his nose pointed toward his chest, he will see only the dirt beneath his nose. The peripheral vision is still performing but he is handicapped in regard to his field of vision just in front of him.

Some experts say that a headset which positions the horse's head vertical to the ground is a positive indication of the horse's softness or submission to the rider. Their thinking is that the horse may be more attentive to the rider with his head in such a position, because his ability to see is limited and he must place his trust with the rider to avoid being in harm's way. Riders are persuaded to look up and ahead, not down the horse's neck to compensate for the horse's lack of skill in this regard. A horse may exhibit uneasiness and resistance when asked to comply with an unnatural headset.

Experiments have been conducted to evaluate the quality of a horse’s visual acuity. A group of horses were trained to choose between pictures of vertical black and white stripes of different widths. The researchers kept narrowing the width of the stripes until the horses showed they could no longer detect the difference. Findings were obtained by measuring brain activity during the testing. The average V.A. was determined to be 20/30 Snellen level. This is the same requirement that humans must pass in order to obtain a driver's license in most states. In comparison, a dog's vision is 20/50, a cat, 20/75, and rats, 20/300. A horse's night vision may not be as sharp as an owl, for instance, but is probably better than a human. Horse's eyes are sensitive to low or dim light which enables them to see reasonably well at night. There are many accounts of horses in the wild that gallop through rough terrain at night with no difficulty. Also, horses can adjust to major differences in brightness and shadows quite efficiently.

Unfortunately, specific situations may affect their reactions to a great degree. The reason a horse may hesitate on entering a darkened doorway or confused by a log on the trail as the rider is passing from a bright field into an area consisting of darkened trees might be because his sense of dark adaptation may not be very keen. That horse may need more training to develop more confidence in such situations. The retina of a horse, as in humans, contains a distribution of rods but not as many cones that exist in humans and other animals. Researchers ascertain that horses do seem to see some colors but they are color blind to many colors that humans can detect. Dr. Hanggi, in a soon to be released thesis, feels that horses have a red/green deficiency. She states that "they are capable of seeing particular objects themselves even if the color of the object is the same as the background color. Color deficiencies do not make objects invisible.”

Pam Fisher is a young lady of my acquaintance who has been involved in equestrian events since the age of twelve. Her entire adult life has been dedicated to the good and welfare of horses as a rider, trainer and therapist. As a result of recent qualification contests, Pam will be a finalist in the coveted Rolex International Equestrian Competition which will take place in 2012. Our readers are invited to peruse her web site at: www.ruffianstables.com

Pam tells me of an instance wherein a well bred mare was born blind. "She was so well bred to race that her owners decided to breed her,” said Pam. “They dug a ditch around the perimeter of her pasture so that she would know not to cross the ditch which prevented her from running into the fence. When she was a foal, her mother taught her the boundaries of the field. She could run full speed and never hit the fence or fall into the ditch. She went on to breed and have her own babies. One of the breed that I was aware of was a very successful race horse called ‘Songlines.’” Pam's narrative can only serve to strengthen our belief in the world of horses and their ability to adapt.

In a dark corner of some stable, somewhere, equine aficionados ask the hard questions: "How do horses see us? Are we their friends or foes? Are we considered their leaders or subordinates? Do they see us as predators or partners? Do we place them in constant danger or can we be trusted? In addition to Dr. Hanggi and Dr. Alison, there are a number of equestrian journalists who continue to pursue the answers to those questions regarding both the horse's behavior and vision. Time and the tide of ever increasing knowledge promises to unravel the mysteries that exist in the relationship between the horse and human.