More than Meets the Eye - Understanding Equine Vision
Vision is very important to your horse. Having developed as open range prey animals that are active during both day and night, horses have traditionally used their vision as a means of staying alive. Detecting predators and staying one step ahead helps keep horses safe and sound, and is the reason why sudden movement from a dog in a nearby bush can send your horse running for the hills.
The Equine Eye
Horses have very large eyes that are located somewhat laterally on the sides of the face, which gives them an extensive field of vision. Each individual eye has about 145 degrees of monocular (single-eyed) vision, and both eyes overlap for about 80 degrees of binocular vision straight ahead. This leaves your horse with two blind spots where he doesn’t automatically see things. These areas are right behind him (in the tail area) and directly in front of him.
Horses have a horizontal pupil (as opposed to a vertical slit-type pupil) that allows them to rotate their eyes and scan the horizon even when they graze. The horizontal shape is common in grazing animals; not only does it give them an advantage in spotting predators while grazing, but it also aids them in making a sure-footed escape.
Eye color is not a factor in horse vision. Light eyes have long been thought to be “weaker,” but there is no evidence for that. Blue eyes do tend to dilate faster and hold dilation longer after a veterinary exam, though.
When free jumping a horse, watch as he approaches the jump. With no rider influence, you will see him adjust his head position as he gets closer to the fence. The horse may raise or lower his head, or do both, working around that front blind spot to get the most accurate idea of the obstacle. By raising his head, the horse gets the most benefit of the binocular vision, with both eyes working to evaluate the jump. With the head held at a vertical position, the binocular vision is focused more toward the ground.
How Well Do Horses See?
Horses are felt to have reasonable vision acuity. Ideal human vision is 20/20; horses seem to be about 20/30 to 20/60, but since they aren’t reading the fine print on the grain bags, that’s okay. Some studies have shown a difference in vision of domestic vs. wild horses, with wild horses more likely to be farsighted and domestic horses more likely to be nearsighted.
Horses, however, have better vision than people in low-light situations. The large size of their eyeball lets the eye bring in the maximum amount of light available in the situation. The equine retina also has adaptations for detecting motion even in very low light – motion such as the stalk of a predator, or more likely for most domestic horses, the flag waving over at the neighbor’s house. In fact, horses can pick up the slightest movement anywhere in their visual area. This helps to explain why a horse is spookier on a windy day; he is simply receiving so much motion-related visual input that it’s hard to process what’s important and what’s not.
When it comes to color, horses don’t really need full-color vision like birds, which use color for identification and breeding strategies. Horses can identify some colors; they see yellow and blue the best, but cannot recognize red. One study showed that horses could easily tell blue, yellow and green from gray, but not red. Horses also have a difficulty separating red from green, similar to humans who experience red/green color blindness. Horses still see red things – they just appear as an intermediate color or even as gray.
Contrast, as opposed to color, is very important to a horse vision-wise; although, color vision can become relevant in some situations where contrast is important. For example, jumps designed with contrasting colors will help a horse to safely clear the obstacle. For optimal safety, course designers must consider both bar color and the background against which a horse will look at an individual jump.
With a general knowledge of how your horse sees, you will be able to better understand his limitations, why he acts the way he does and be prepared to deal with his reactions. Happy Riding!
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