Equine Vision - Visual Capacity of The Horse - Visual Field

Visual Field

Like most prey animals, the horse's eyes are set on the sides of its head, allowing it close to a 350° range of monocular vision. Horses have the largest eyes of any land mammal, and are lateral-eyed, meaning their eyes are positioned on the sides of their heads. This means horses have a range of vision of more than 350°, with approximately 65° of this being binocular vision and the remaining 285° monocular vision.

This provides a horse with the best chance to spot predators. The horse's wide range of monocular vision has two "blind spots," or areas where the animal cannot see: in front of the face (making a cone that comes to a point at about 3–4 ft in front of the horse) and right behind its head, which extends over the back and behind the tail when standing with the head facing straight forward. Therefore, as a horse jumps an obstacle, it briefly disappears from sight right before the horse takes off.

The wide range of monocular vision has a trade-off: The placement of the horse's eyes decreases the possible range of binocular vision to around 65° on a horizontal plane, occurring in a triangular shape primarily in front of the horse's face. Therefore, the horse has a smaller field of depth perception than a human. The horse uses its binocular vision by looking straight at an object, raising its head when it looks at a distant predator or focuses on an obstacle to jump. To use binocular vision on a closer object near the ground, such as a snake or threat to its feet, the horse drops its nose and looks downward with its neck somewhat arched.

A horse will raise or lower its head to increase its range of binocular vision. A horse's visual field is lowered when it is asked to go "on the bit" with the head held perpendicular to the ground. This makes the horse's binocular vision focus less on distant objects and more on the immediate ground in front of the horse, suitable for arena distances, but less adaptive to a cross-country setting. Riders who ride with their horses "deep", "behind the vertical", or in a rollkur frame decrease the range of the horse's distance vision even more, focusing only a few feet ahead of the front feet. Riders of jumpers take their horses' use of distance vision into consideration, allowing their horses to raise their heads a few strides before a jump, so the animals are able to assess the jumps and the proper take-off spots.