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Because of their vision capabilities allowing for a panoramic view, it is impossible to sneak up on a horse.īinocular and Monocular Field of Vision in a Horse A horse’s depth perception is considerably less than for humans. The binocular field is responsible for depth perception. The monocular fields straight in front of the horse’s face overlap slightly resulting in a binocular field between 65 and 80 degrees. Each eye sees across an arc of approximately 200–210 degrees around the body at one time. Monocular vision allows the horse to see on both sides of his head, meaning the left eye and the right eye work independently and see different views. Horses use two-forms of vision, monocular and binocular. Anything that moves, regardless of what it is, may cause the horse to initiate the flight response before a predator begins to approach. The motion of anything causes the horse to register what it is (a survival mechanism for the prey animal). Horses are equipped to be highly aware of peripheral motion. This explains why horses are sometimes reluctant to enter dark places, such as a unfamiliar building, stall or trailer. Horses’ eyes are not adept at making a quick transition between bright and dark locations. This may cause the horse difficulty in identifying details and smaller objects and moving ones may trigger the flight response. Because light is magnified, the pupil must constrict more during sunlight to protect the eye. As a result, the horse is able to see at lower light levels but the reflections also blur images by reducing the resolution. When light enters the eye, it triggers a photoreceptor on the retina, which is reflected by the tapetum to trigger additional receptors. The horse's night vision is superior to humans due to the tapetum lucidum, which enhances visual sensitivity under low light conditions. Visible Sprectum Between Humans and Horses Thus, they see blue, green, and variations of the two colors, but do not see red or shades of red.
![predator eyes vs prey eyes human predator eyes vs prey eyes human](https://i.imgur.com/Rj3jIdV.jpg)
Horses can see only two of the visible wavelengths in the light spectrum because they have only blue-sensitive cone cells and yellow-sensitive cone cells. Humans have three types of cones, which sense red, yellow-green, and blue light. The retina also contains cones, or cells that sense color. Thus, equine retinas are designed to detect motion even in low-lighting conditions.
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The horse’s ratio of rods to cones is approximately 20:1, compared to people who have a ratio of 9:1. Cones are required for bright light (day light) vision, and rods are required for dim light vision. Horses are thought to have vision somewhere in the range of 20/30 to 20/60. Compared to other animals, horses have lots of cells in their retinas and have fairly good vision. Pupils contract under bright light and enlarge in low light. The size of the pupil determines the amount of light allowed into the back part of the eye. The horse has a rectangular pupil shape which extends the area of visual perception. The retina is the major determinant of vision. It is a knobby structure that juts out from the top of the iris and functions to shade the pupil from glare. An unusual feature of the equine eye is the corpora nigra. The nasolacrimal duct drains the tears to a small opening just inside the nostril. Eyelids have tear glands that keep the eye moist. In combination with the upper and lower eyelid, all three function to protect the eye. The third eyelid is a pink membrane that moves over the eye from the inside corner to the outside corner. Eyelids are a thin ring of two layers of muscles that relax and contract to open and close the eye. The cornea is the surface of the clear part of the eye and the colored part of the eye is the iris. The eye of the horse set to the side of the face Unlike humans, the horse is able to see images to the left and right at the same time due to the eyes being at the side of the head. From most angles, horses cannot get a left-eye and right-eye view of the same object in one glance. A horses’ ability to see depth is limited because their eyes are set so far apart. The position of the eyes on the horse’s face accounts for differences in how horses see, dictate visual range, peripheral motion detection and depth perception. The equine eye is eight times larger than human eyes placed on the sides of their head. Horses use vision to orientate themselves, detect motion and distance, and evaluate the consistency of the environment. By scanning larger areas, prey is safer from a surprise attack from a predator. Prey species are designed for scanning the environment compared to picking out sharp details. The horse is a prey animal, relying on their senses to assess their environment.