As predators, humans have both eyes on the front of the face and use binocular vision.
We see clearly what is directly in front of us and we have good peripheral vision which gives us a total visual field of 180 degrees on a horizontal plane.
Our vertical vision is much less and we need to tip our head up or down to see the sky above us or the ground below us.
We see in vivid colors but our night vision is only fair.
Our visual acuity is 20/20.
As prey animals, horses have eyes that are set wide apart and sit on each side of the head.
They use both binocular and monocular vision.
Objects in front of them are seen with the binocular vision, meaning they see the same object with both eyes at the same time, just as we do.
This allows them good depth perception and an acuity of 20/40.
There is an overlap with binocular vision that gives a visual field of 70 to 90 degrees in front at a distance of around two to four feet.
They have good night vision but are unable to adjust readily from light to dark.
This may be one reason why they are reluctant to enter a dark trailer.
As objects move to the side, monocular vision takes over.
This means that the eye on each side sees a different object yet the horse is able to focus on each one at the same time with only a slight loss of visual acuity.
As with humans, as objects become farther away, they appear less clear.
This probably accounts for spooking at objects that suddenly appear in the distance.
Anything not clearly seen is perceived as a predator.
The field of vision of each eye is about 170 degrees both horizontally and vertically which gives them a global vision side to side and top to bottom of 340 degrees.
With only a slight movement of his head, the horse can increase this to 360 degrees.
Thus, he is able to graze and spot predators at the same time.
He does, however, have some blind spots.
Because his eyes are on the side of his head he can not see directly in front of his face between his eyes as humans can.
This may be why he startles when you reach up to scratch his head and why is head shy.
He can not see directly behind him and this is the reason you should not walk behind him unless he knows you are there.
He can not see under his chin, nose, neck or under his belly and the sudden sensation of your touch in these vulnerable areas screams predator to him until he learns to accept your touch.
He can not see his back and again, touch or pressure from a saddle means a predator in his opinion.
Remember, a predator would pounce on his back or latch on to his throat or attack his belly.
It is no wonder these are sensitive areas.
If you watch your horse you will see him raise and lower his head and turn it from side to side in order to focus on an object.
Riders need to understand this and how he sees while being ridden.
Because horses can not see anything below their chins, jumpers can not see the jump or the landing on the other side once they have left the ground.
They must put the utmost trust in their rider.
In Western Pleasure, when we ask the horse to bend at the poll while showing, he can no longer see in front of him.
He sees only the ground and must depend entirely on his rider for guidance and direction.
On the trail he sees objects in front of him with binocular vision.
As he approaches the object he uses monocular vision and looses some focus.
If given his head so that he can turn enough to use binocular vision he is less likely to bolt.
If we understand how he sees the world around him, we are better able to understand why he reacts the way he does.
With this understanding, we can better accommodate his needs to make him feel safe and keep ourselves safe both on the ground and in the saddle.