Today on the program we are going to talk about vision in horses and what a horse sees and doesn't see compared to humans. First of all, vision is not just about the eye itself as it has to do transmission of the information to the brain, and the brain processing the information. Dr's. Paul Miller and Chris Murphy indicate that because horses have one of the largest eyes of all land-based animals, they allow more light to enter the eye, which greatly improves their vision in dim light situations. The pupil and cornea are also elongated horizontally, which again increases admission of light to the eye. The horse's pupil can dilate six times larger than the human's pupil.This is why the horse can see objects at night that humans can not see. However, the horse's depth perception is much worse than humans because much of the horse's visual field involves only one eye. Only about 70 percent of the horse's vision utilizes both eyes so this decreases depth perception. This is the reason many horses balk when seeing objects as they can not tell how far away they really are.
The horse's visual acuity is not as good as humans because by having the increased ability to see at night decreases the accuracy of their vision. A person whose eye tests indicate 20/20 vision means that the test subject can see objects from 20 feet that a person with normal vision could see at 20 feet. And a person with 20/100 vision could see an object as close as 20 feet what a person with normal vision would see as far away as 100 feet. In comparison, the horse's vision is believed to be from 20/40 up to 20/60. So a horse would have to be 20 feet from an object to see it with the same clarity as a person at 60 feet.