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head and neck go through a coordinated rhythmical mo- tion to stabilize the eyes while a horse trots and canters. Horses can’t wipe their eyes but must keep them free


from debris and rain in inclement weather. So beyond simply blinking their eyelids, horses also have a third eye- lid that sweeps across the cornea removing any debris as needed. The horse's visual acuity, the ability to see details of


corpora nigrans and it is thought this acts as an internal visor blocking glare and thus enhancing daytime vision. In a manner similar to sun glasses, parts of the lens con- tain yellow pigment which filters out bright light. Additional adaptations


reflect the need for a wide field of view and ability to maintain vision while in motion. To aid them, their eyes have evolved to be widely set. They can see in both a monocular way (with one eye) and binocu- lar way (with two eyes). Their widely set eyes can


in many ways to men who are color blind. Many men having trouble distinguishing between red and green. Horses seem to have trouble distinguishing between blue and orange. Cones are the cells that


see 190 degrees in the hor- izontal direction and 170 degrees in the vertical di- rection. This gives them a range of over 350 degrees with small blind spots that can be overcome by shift- ing the head slightly. The degree of binocular (two- eyed vision) overlap is 55- 65 degrees. It rivals or ex- ceeds that of dogs. Horses use both monocular and binocular clues to estimate depth, although the binoc- ular depth perception is 5 times better than for one eye. As the horse moves it needs to maintain its sight in or-


der to properly access a jump in front of them. To keep their vision from bouncing you can watch as the eyes,


ian serving the Silicon Valley and surrounding areas for over two decades. He is also an active show jumper, competing with his horse “Kolor Me Fabulous” in the Amatuer-Owner Jumper Division and in Grand Prix. He can be reached at 800-998-4650 or at drdoug@novickdvm.com. More information is available at www.


Dr. Douglas Novick DVM is a performance horse veterinar-


sense colors and horses have dichromatic color vision with two cone types: blue sensitive cones, and yellow sensitive cones. Humans in contrast have three types of cones blue, green, and red. That contrast means horses have a less ac- curate perception of other colors. It is probable that their color


ders which impair vision in other species, but because of the crudeness of the tools veterinarians currently have available to determine how well a particular horse can see. The future can change that.


sense results in colors appear- ing as washed-out pastels. Ob- jects can be differentiated from their surroundings if they are suitably different in any one of five different aspects: bright- ness, motion, texture, depth, and color. Clinically it is difficult to rec- ognize anything but the most massive visual impediments in horses. Not because the horse is unusually resistant to disor-


an object, is among the best of the domestic mammals and better than that of many people. From 6 feet away horses can detect small differences in depth, which ap- proximates the ability of a cat. Their color vision is another story. Horses are similar


novickdvm.com Dr. Novick is a graduate of Tufts University School of Vet-


erinary Medicine, Boston, Massachusetts, and received his under- graduate degree from Duke University where he was graduated Phi Beta Kappa, summa cum laude.


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