them, making them panic before they realize what the object is; for example, a truck driving by with a flap wildly moving in the wind.”
Horses notice movement very well with their acute
peripheral vision but, with their eyes set so far apart, they have limited depth perception and can’t focus well on some- thing that is up close. “While we can go from seeing some- thing far away to something near us relatively easily, horses can’t change their focus very much by manually compress- ing the lens; they don’t have that ability, so they scan their surroundings more and look for movement rather than seeing well-defined objects. They don’t have to read the newspaper so that kind of focus falls by the wayside,” Dr. McMullen explains.
Vision and Performance A horse can improve depth perception slightly by raising their head or lifting their nose, which can be problematic in performance horses because this tends to hollow the back as well. Many jumpers lift their head in the approach to the jump to get a glimpse of what is in front of them and deter- mine its height and width. Warmblood horses in particular tend to be afflicted with
near-sightedness, explains Dr. McMullen. “A horse that is 2 or 4 diopters myopic (near-sighted) cannot focus the incom- ing light onto his retina. The incoming light comes to a focus somewhere within the vitreous, in front of the retina. This results in a blurred image for the horse, especially in the distance. Thus, the horse doesn’t see the world like a horse with a normal refractive state would. We tend to see that a lot in Warmbloods.” Interestingly, he states that one of the things he has
observed is that horses with strong refractive errors are very calm and they have a very strong relationship with the owner or trainer. (Refractive errors result when incoming light is not precisely bent, resulting in the light being focused in front of, or behind the retina, i.e., nearsightedness and farsighted- ness, respectively.) He says that horses will often perform well with their usual rider, but if they are sent to a new trainer all of a sudden they may have problems and may be labeled as difficult.
“Some common patterns of behavior associated with
refractive anomalies (errors) may become apparent to the owner or trainer. Horses may have a hard time transition- ing from light vs. dark, and they may overreact to the pres- ence of a puddle of water or something shiny on the ground. Sometimes horses tend to crane their necks quite a bit—if for example the right eye is affected they might turn the head to the right to give the left eye a better view.”
Early Signs of Eye Problems Eye problems, like most ailments, are much more easily treated when they are caught early. “If you suspect a prob- lem, you want to call the vet right away. A lot of eye problems benefit from early intervention; if you can treat a corneal ulcer the day it happens, you’re less likely to get a fungal infection or an abscess,” Dr. Moding explains. As a horse owner, there are a few things to pay attention
to so that you can quickly detect developing problems with your horse’s vision. Dr. Moding says behavioral changes can be the first indi-
cation that something is not quite right with your horse’s vision. “Some people notice that there’s a change in the amount their horse is spooking, or a jumper is hitting rails more often than usual,” she says. “The biggest thing is really looking for a change in behavior— for example tripping over a pole or brushing up against the arena fence as you’re riding. Horses usually see pretty well around them, so spook- ing and running into things are behavioral indicators. If a horse has been behaving unusually I always take a quick look in the eyes to make sure that’s not a factor.” Dr. Gardner agrees behavior changes are often an early
sign of vision problems. “One of the first things we notice is a change of behavior in different lighting. Especially as a horse goes from blacktop to an arena surface or from light to dark, such as from sunlight into a barn, they might be uncer- tain of the footing because with less light they are unable to see details,” she says. “That can be a sign, for example, of cataracts or that a horse is losing his sight due to uveitis. People also notice horses become spooky because as vision decreases they might not notice something until they’re closer to it.”
Horses often lift their heads as they approach a jump to see it more clearly. Here is Great Britain’s Ben Maher riding Don Vito at the HITS Ocala $1 Million Grand Prix in March 2017.
38 March/April 2018
Photos by Ed Haas
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