Using Monocular and Binocular Vision
Another fantastic feature of the horses’ eyes is their monocular vision. Rather than using both eyes to focus, they use one eye to get a clear picture. Humans have binocular vision, but a horse has both binocular and monocular. However, they only use their binocular abilities when viewing objects from the front. Remember, they can see all the way around their body.
Dr. Jake, our resident veterinarian, says that horses are easily spooked because they see things again for the first time. It sounds confusing to you, but since they only use one eye to focus, when the second eye gets a glimpse of something that has already past, it can cause a reaction. Though a horse doesn’t commonly use both eyes to see, it’s easy to tell when they do. They position their ears pointing straight ahead using both eyes.
How Does A Horse Focus?
Focusing these all-seeing eyes takes a little work. Inside the eye, there are tiny muscles that help the lens. Moving his head about will allow him to direct the object to the correct part of the lens for a sharper image. For instance, if an object is far away, he will simply raise his head to bring it into focus. To see objects that are closer in range, he will need to lower his head. When you observe the horse’s head going up and down, he is merely trying to bring clarity to his sight. Any restriction to the natural movements will throw his field of vision off. If he cannot see an object, he will shake his head to bring it into focus.
Their Magnificent Field of Sight
A horse has the largest eyeball of any land mammal. This extra-large peeper magnifies an object fifty times larger than what you can see. The advantage to this unique feature is that they can see things in vibrant detail. In the wild, they have an advantage over their prey because their keen perception helps them to spot a predator.
Depth perception is a bit tricky for a horse. Humans have binocular vision that allows them to distinguish depth, but for a horse, things are different. They can indicate the distance of an object merely by comparing it with the known size. For instance, they know how large a human is, and if the human is smaller than average when looking through their monocular vision, then they can perceive that they are far away. If they look at an object and it doesn’t appear within a normal range, then they will turn their head to use their binocular vision to get a more accurate image.
When it comes to seeing in the dark, the horse has superior night vision. Unfortunately, they have a difficult time seeing during the twilight hours. Humans can see much better because of their ability to distinguish color. The horse doesn’t have the best color identification when the natural light diminishes. They can see hues of yellow, green and blue, but red is hard for them to differentiate. During the early evening hours, they may accidentally bump into the gate or one of the other horses in the pasture. The dimmed color perception only lasts till nightfall. Until their night vision engages, they will have difficulties with tasks.
Compensating for Blind Spots
Horses have two blind spots, one in the front of their muzzle and the other behind their tail. The top of the muzzle is a place where you would think they could clearly see. However, the position of the eyes creates this anomaly. They prefer to be approached from the side so that they can keep you in clear view. They avoid head-on-approaches to make sure they can see without something being in one of their blind spots.
A horse cannot see anything within six feet of his tail. To counteract this anomaly, the horse will turn their body to help bring the object into focus. If you approach from behind, make sure that you are quiet and don’t do anything that will startle them. When you are in the proper vision field, you won’t spook them.
Understanding Dichromatic Vision
There’s no denying that a horse’s eyes are indeed unique. Groomers must pay particular attention to their eye area during a trim. They have sensory hairs that help to trigger their blinking reflex. These hairs need to be about an inch in length to work effectively. If they are too short, they can damage the surface of the eye when they are doing simple tasks like drinking.
Though we still don’t have 20/20 vision on what a horse perceives, we do know that they have a fundamentally different view of their surroundings. Their dichromatic vision is something that we may never fully understand, but by observing and conducting further studies, one day we may have a clear picture.