Your Horse's Vision

By: Lorelei Prichard DVM
About the author

Horses have been man’s companion for thousands of years, and their long-standing relationship has been documented in the earliest of primitive cave drawings. They’ve plowed our fields, transported us to new beginnings, and provided sport, entertainment and friendship. There is nothing in human experience the horse has not born witness to, and it’s only natural that we would want to know how our horses view the world we live in. It has been said that the eye is the window to the world.

It is generally accepted that the visual experience of a horse is quite different from that of his human companion. This is due to several physical differences.

Whereas human eyes are centered on a relatively flat face, the horse has eyes located on either side of a long, narrow head. This unique placement allows for greater perception. In fact, the horse has an amazing 350-degree field of vision. Simply stated, your horse can almost glimpse his tail without turning his head. This pastoral vision provides the grazing horse greater observational ability and protection against predators. This was a necessity for the early horse that was constantly on the lookout for danger.

Horses do not have the same visual acuity that their human companions have. The equine lens is responsible for focusing an image upon the retina just as in the human eye, and this is accomplished by altering the lens surface by the ocular muscles. Because the horse has a less sophisticated system of manipulation and an extremely large lens, he is unable to focus as clearly as we do. The eye of the horse is normally shortsighted resulting in dim, poorly focused vision. It has been suggested that the horse’s normal vision would compare to the human equivalent of 20/33.

One of the greatest differences between our vision and our horse’s is the absence of three color vision. Those of us who are not handicapped by “color-blindness” have the ability to discern the colors blue, red, yellow, green, and mixtures of these. Normally, a human can distinguish about 10,000 discernable colors.

The retina contains the photoreceptor cells necessary for vision and houses the rods and cones essential for interpretation of a visual image. The rods are highly sensitive to all wavelengths of light, are adapted for diffuse vision in dim light, and are the most abundant photoreceptor cell found in horses. The cones are necessary for daylight and color vision. Each cone is sensitive to different wavelengths of light and provides a specific color experience. The hues and mixtures of color we visualize result from the reactions within our three different retinal cones to the varied wavelength and intensity of the light entering our eye. These cells provide us with the broad spectrum of color we enjoy.

Whereas humans possess trichromatic vision, horses possess only two different cones, and the absence of this third cone limits your horse’s color sensitivity. Color perception for those with dichromatic vision is limited to shades of blues, yellows and grays. This is similar to what a human that is red-green color-blind might see. This lack of red-color perception is why hunters can wear bright orange vests and still be elusive to the hunted.

Our equine companion sees his world through a unique window. The horse’s peripheral vision is enviable, and although his surroundings may not appear as colorful and focused as we perceive, his visual experience is adapted for his needs. Knowledge of the horse’s visual advantages and limitations provides us with a greater understanding of his habits and interactions.

Copyright © 2010 Lorelei Prichard, DVM