Horses are pretty remarkable creatures. Have you every wondered why they do some of the, seemingly silly, things they do? Like, why does my horse spook at something we JUST walked past a few minutes ago? Well, it has a lot to do with their eyes.
Horses can see nearly 360º around them. This is because their eyes are on the sides of their head. This helps them to always be aware of when a predator may be in the area, so they can flee potential danger. However, horses do have a couple of blind spots. This is directly in front of their muzzle and about 6ft behind their tails. This explains why they tend to scoot around to see what is behind them or shy their heads to the side to see what is in front of them.
Horses have mostly monocular vision. This means they see things with one eye rather than with both at the same time, like we do. Humans see in binocular vision and horses can do this as well but only with things in front of them. For everything else, they see it with one eye and then the other. This is why your horse may be afraid of something they already walked by a few minutes ago. They are now seeing that thing for the first time with their other eye. When horses are focusing on something with both eyes instead of just one, they are looking forward with both ears up.
Horses can change what is in focus by using the muscles in their eyes to change the shape of their pupils (like we do), or they can move their head position up and down to change focus. The top part of their vision is reserved for far away objects and the bottom part of their vision is for up close objects. This is why when your horse spots something across the field, they will have their head up the air to try to focus on whatever they are seeing. Conversely, they will put their heads down to try to focus on something that is closer to them or lower on the ground. They aren't being fresh or stupid, they're just trying to assess their surroundings.
Horses have the largest eye of any land mammal. Only whales, seals and ostriches have larger eyes than horses. Having such a large eyeball enables them to see distance objects in much clearer detail than humans can.
Depth perception works a bit differently for horses. Binocular vision what enable depth perception. Since horses are mostly monocular visioned, they have to gauge the distance of an object by comparing it to the size they already know that object to be. For example, they know humans are a certain size relative to themselves and other things in the area. If they see a human that is smaller than they are used to, then they will determine that human to be far away. So if your horse sees something with one eye and it appears to be a different size than they are used to, they will turn their head and body to get a better look at that object with two eyes instead of just one. Maybe this is why some horses are afraid of mini horses, because they aren't the size they are used to horses being?
Horses have great night vision! Even better than a cat. However, In low light conditions, like dusk, their vision can be a bit hindered. This is because horses can see just a few colors (yellow, blue, green and red is questionable). Around dusk, their color vision has diminished, but their night vision hasn't quite kicked in yet.
Sensory hairs around your horse's eyes trigger the "blink reflex" if he gets too close to underbrush or other possibly eye-damaging surfaces while grazing or drinking. So when you're grooming, even for shows, avoid trimming these hairs.
So there you have it! Horses have some pretty unique eyes and it explains many of their unique behaviors. Hopefully this allows you to be a little more forgiving when your horse "spooks" at something you find silly.
Information and inspiration for this article can be found here.