7 Insights into Equine Vision
1. From light to images. As light enters the horse’s eye, it passes through the cornea, aqueous humor, lens and vitreous humor. These structures refract, or bend, the light and focus it onto the retina. At this point, the light is converted to an electrical signal that travels out of the eye, along the optic nerve, to the brain. The brain interprets it as images, or vision.
2. Binocular and monocular vision. The horse’s eyes are placed on the side of his skull, giving him a wide arc of monocular vision on each side and a roughly 65-degree arc of binocular vision in front. With monocular vision, the horse sees different things through each eye, although the brain shares the information from each side. (This lays to rest the myth that what a horse sees with one eye isn’t recognized through the other eye.) Binocular vision allows the horse to see the same thing with both eyes at once. With this wide range of vision from monocular and binocular viewing, horses can see more of the world around them at any given moment than a human. When your horse spooks or startles, it may be caused by something you can’t see without turning your head.
3. Blind spots. This eye placement also gives the horse blind spots—notably behind himself and for a space of about 4 feet in front of him. To adjust for this front vision limitation, a horse will naturally raise, lower or tilt his head to see better—which could explain why so many horses reflexively move their head upward as you raise a hand to their forehead. It’s also worth noting that a horse ridden with his nose on or behind the vertical cannot see directly in front of himself.
4. Night vision. Horses do have fairly good vision in low-light conditions. That’s because their large eyes, combined with their horizontal pupils, help them capture more light.
5. Color vision. Horses can see some colors, although they probably don’t see them as vibrantly as people do. In general, they can see the green–yellow spectrum and the blue–gray spectrum. They can’t see red.
6. Eye care. To help keep your horse’s eyes in good health, reduce the chance of irritation from dust, insects and UV light. A fly mask may help as well as providing shade during peak sunlight hours. Also work to decrease the risk of trauma by paying attention to stabling and pasture. Low tree branches, thorny plants, hooks or other sharp objects can be hazardous.
7. Signs of trouble. If you notice that your horse is squinting, rubbing an eye or suddenly acting head shy, these could be signs of eye trouble. Also watch for tearing, squinting, redness, cloudiness or lumps and bumps around the eye. If you suspect a problem, don’t hesitate to call your veterinarian since treatment delays could increase the risk of a serious issue.