Understanding how horses see the world is important for anyone who interacts with them, for both personal safety and the welfare of the horse.
Beware of the blind spots
Horses have a nearly 360-degree field of vision and the ability to detect movements that may not be perceived by humans. However, it is important to know that the horse does have blind spots and to be aware of the location and extent of the areas of no or limited vision to avoid injury.
The horse’s blind spots are directly in front of its eyes and behind its body (Figure 1.). Depending on the placement of the eyes, the “blind spot” in front may only be an area of limited vision, rather than a true blind spot. Either way, the blind or indistinct area of vision is widest at the eyes and ends at a point about 3 to 4 feet in front of the horse. While the blind spot at the back is slightly wider than its body and can extend indefinitely if the horse is looking straight ahead.
It is fairly common knowledge that you should never stand behind a horse. Nor is it wise to stand in the areas of marginal vision along its sides, closer to the rear (Figure 1.) for extended periods of time unless you have physical contact with the horse, which can be as simple as a hand placed on its side to let it know where you are. Otherwise, the horse may forget you are standing there and startle when you reappear in its field of vision, which could result in a kick. It is also advisable to avoid standing directly in front of the horse, where it has limited vision at best.
When approaching a horse, you should walk slowly and speak to it to draw its attention to you and avoid startling it. It is best to approach from the side (near the head or shoulder) so the horse can easily re-position its head to see you.
Monocular & binocular vision
Another interesting feature is the horse’s ability to see with both monocular and binocular vision (Figure 1.). The extent of the monocular vision, although flat rather than 3-dimensional, is quite broad and enables the horse to see what is happening on either side of its body and perceive the smallest of movements, which is important in quickly noticing potential sources of danger.
The range of 3-dimensional binocular vision is fairly limited and varies depending on the placement and shape of the horse’s eyes, and thickness and length of the forelock. Because of the blind spot in front of the eyes, the horse’s ability to perceive distance is significantly affected by the position of its head (very important when jumping) and significantly impaired when movement is restricted, as in some dressage positions (Figure 2.).
The horse’s eye has areas of distinct and indistinct vision. The pupil is a wide narrow strip of highly concentrated ganglion cells, the area of distinct vision, and the rest of the eye is an area of indistinct vision. So when a horse perceives movement it will reposition its head to bring the object into focus. The next time you are nose to muzzle with a horse, pay attention to how it tilts its head and looks at you with one eye, it is repositioning its gaze to bring you into focus.
Limited colour vision
Horses do have colour vision, although they don’t see in the same colour spectrum as humans. Whereas the human eye contains 3 types of cones, the part of the eye that processes colour, horses only have 2. Therefore, they have a much more muted colour palette (Figure 3.), as well as lower visual acuity (sharpness of vision). Additionally, studies have found that horses’ eyes respond to green and blue, but not red. Essentially, they see the world in a similar way to humans with red-green colour blindness. Figure 4. below demonstrates what we see (images A and B) versus what horses see (images C and D). The images demonstrate differences in colour perception and acuity only, not field of vision.
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Evans, P. (2010). “Equine Vision and Its Effect on Behaviour.” Equine. Utah State University. Retrieved from http://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1125&context=extension_curall
McGreevy, P. (2012). Equine Behaviour: A Guide for Veterinarians and Equine Scientists. 2nd ed. Edinburgh: Elsevier.
Mesloy, J. (2006). “The Equine Colour Vision Debate.” Equus. Retrieved from http://equusmagazine.com/management/colorvision_012706
National Farm Animal Care Council. (2016). Code of Practice for the Care and Handling of Equines. Accessed: http://www.nfacc.ca/pdfs/codes/equine_code_of_practice.pdf