Horses have large, prominent eyes, the largest of any land mammal. A little understanding in how the world appears from an equine perspective can aid you and your horse in acting together.
Horses and humans see the world differently. The skittish reaction of a horse to a piece of paper skittering across its path on a windy day may be seen as silly to a person looking on, but it’s perfectly understandable if you’re a horse. The person probably never gave a second thought to that piece of paper, yet the horse instinctually reacted with fear and apprehension.
The physiology of horses’ eyesight has evolved to help them quickly locate danger and react appropriately. The equine eye is unique in that it has both monocular and binocular vision. Humans exclusively use binocular vision – that is using both eyes to focus on one thing, and using the images from each eye to blend into one picture. Horses do this as well, but they can also switch to monocular vision – using each eye independently. As a result the brain often is receiving two images at the same time.
So a horse’s eye is adept at detecting movement, and less adept at quickly focusing on an object. They respond first to movement, and then move to a place of safety in order to focus upon the cause of the movement.
This means that when you are riding down the trail and see a strange object ahead, you’ll recognize what you’re seeing long before your horse does. An easy way to know if your horse is using binocular or monocular vision is to see which way his ears are pointing. If both ears are pointing in the same direction, he is focused on one thing.
HOW WIDE IS THE HEAD?
Horses can see almost 360 degrees around them, with the exception of two important blind spots – one behind them and one directly in front of them. The blind spot in front of your horse can vary in length according to the width of your horse’s head. Horses with narrower heads have less of a blind spot, and horses with a wider head have a blind spot of anything up to around four feet in front of them.
Horses have better eyesight than humans in the dark, yet it takes them longer than humans to adapt from light to dark conditions, and vice versa. For a while longer than us, they will not be able to see well until they can focus again, making them feel uneasy.
The prominent eyes of a horse tend to be more prone to eye injuries than other domestic animals. Foreign bodies such as splinters, grit or grass awns also become lodged in the eye. Since the cornea, the clear, thin outer layer of the eyeball, is so prominent it commonly sustains the brunt of the injury.
Eye injuries are extremely painful, causing the horse to squint, and hold the eyelids shut very tightly. Excessive tears and discharge run down the bridge of their nose. The eyelids may swell, and redness can occur in the white part of the eye. The accompanying inflammation that follows injury usually results in a grey, cloudy film within the cornea. This whitish-grey film is a bandage of sorts, bringing with it healing elements. Once the wound is healed the discolouration fades. This may take days to months to completely resolve.
As healing advances the eye once again becomes quiet with the squinting, tearing, discharge and redness becoming less. Keeping the horse in subdued light, or creating a temporary patch by duct taping a fly mask over the affected eye, provides comfort and relief to the healing eye. A warm compress infused with a few drops of lavender oil held over the eye is also a soothing practice. Talk gently to a horse with an eye injury; it is reassuring.
A horse with an eye injury is best examined as soon as possible by a veterinarian to determine the extent of the injury, and a treatment plan. A complete examination of a painful eye often requires sedation. The type of therapy used is dictated by the type and extent of the injury, complications encountered, and the disposition of the horse. With appropriate treatment, most corneal injuries have successful outcomes.
Carol Shwetz is a veterinarian specializing in equine practice at Westlock, Alberta.