By Laura Michaels, Pony Wrangler at Cape Hatteras National Seashore
Although the structure of a pony’s eye is similar to that of many mammals, it is almost the largest eye of any living creature, including whales and elephants. A pony’s eye is twice the size of a human’s.
A pony’s vision is quite different from ours. We have a 180-degree field of vision and because our eyes are on the front of our heads, we use binocular vision. The position of a pony’s eyes on the sides of its head afford it greater peripheral vision, similar to that of other prey animals. Ponies see with monocular and binocular vision. Monocular vision means that each eye has a separate field of view. With each eye, a pony can see to the front, to the side, and to the rear.
Binocular vision means that each eye supplies an image and they are superimposed to create a three-dimensional picture. In order to use binocular vision effectively, a pony must be able to move its head and neck freely.
When a pony grazes, constantly moving its head from side to to side, it virtually has a 360-degree field of vision. Its view to the rear is blocked only by its relatively narrow lower legs, so it needs to turn slightly or rotate its head as it grazes to see behind itself.
As mentioned, ponies have very good peripheral vision, especially with their heads down. When a pony’s head is up, however, it has several significant blind spots:
- Directly behind it, in the area of its tail
- Directly under its head or nose
- On its back, in the vicinity of its withers
- Directly in front of its forehead
Light and Dark Adaptation
Although ponies take longer to adapt to changing light conditions, their range of adaptation is better than humans. This is due to the sheer size of a pony’s eye and the large retina surface for light reception. Also, a pony’s pupil can dilate six times larger than a human’s. Ponies have night vision as good as an owl’s or a dog’s, but not as good as a cat’s or a bat’s.
The pupil’s narrow, horizontal configuration in bright light tends to decrease the amount of light entering the eye from above (the sun and sky) and below (reflection of the sun on the ground or sand). In addition, a horse’s long, downward-angling eyelashes help act as a sunscreen or visor.
Since depth perception is only possible in the binocular field of vision, and since a pony’s binocular field is much smaller than a human’s, a pony’s depth perception is not as good as ours. When a pony is free to raise its head to really look at something, it is able to use the area of its eye with the greatest depth perception.
The pony’s eye has two types of cone cells in the retina that are sensitive to color whereas a human eye has three types of cone cells. Whether ponies can see colors as we do is still widely debated. Most researchers agree that ponies do have more than “shades of gray” discrimination but not the color range of humans. Exactly which colors ponies see is still unresolved.