Horses have a mix of monocular and binocular vision. https://www.equisearch.com/articles/...n-and-eyesight
"The horse has a "visual streak", or an area within the retina, linear in shape, with a high concentration of ganglion cells (up to 6100 cells/mm2 in the visual streak compared to the 150 and 200 cells/mm2 in the peripheral area). Horses have better acuity when the objects they are looking at fall in this region. They therefore will tilt or raise their heads, to help place the objects within the area of the visual streak." https://en.wikipedia.org/wiki/Equine...y_of_the_horse
That suggests horses have decent vision in their visual streak, and poor vision outside of it. My THEORY is that much of their vision acts like a motion detector. Once alerted by the motion detector, they move their head to actually SEE what caused the motion. If the motion is too near them, they will move first and then look.
It also suggests they have good binocular vision and depth perception IF they can use their heads to adjust their vision. I have the same issue sometimes wearing bifocals....
"The researchers found that horses, when using both eyes, could perceive a depth difference of about 10 centimeters when viewed at a distance of 200 centimeters. Cats and pigeons show about the same ability.
" - The Nature of Horses, Stephen Budiansky, pg 122
The same source says horses could be trained to respond to differences based on depth while wearing 3D glasses.
I spend a fair bit of my riding twisting between cactus. While I said before that their eyesight seems to function as a motion detector over much of the range of vision, their behavior dodging cactus indicates I'm wrong. I've had my horse continue looking ahead while placing his feet and body within inches of cactus while twisting back and forth. I have no idea how he manages to be so precise. I can understand it with his front legs, but I've watched cactus spines pass within inches of my legs and inches of his hind legs, while turning, and no errors yet.
There are more things in heaven and earth, Horatio,
Than are dreamt of in your philosophy.