7 In­sights into Equine Vi­sion

Practical Horseman - - Inside Your Ride -

1. From light to im­ages. As light en­ters the horse’s eye, it passes through the cornea, aqueous hu­mor, lens and vitre­ous hu­mor. These struc­tures re­fract, or bend, the light and fo­cus it onto the retina. At this point, the light is con­verted to an elec­tri­cal sig­nal that trav­els out of the eye, along the op­tic nerve, to the brain. The brain in­ter­prets it as im­ages, or vi­sion.

2. Binoc­u­lar and monoc­u­lar vi­sion. The horse’s eyes are placed on the side of his skull, giv­ing him a wide arc of monoc­u­lar vi­sion on each side and a roughly 65-de­gree arc of binoc­u­lar vi­sion in front. With monoc­u­lar vi­sion, the horse sees dif­fer­ent things through each eye, although the brain shares the in­for­ma­tion from each side. (This lays to rest the myth that what a horse sees with one eye isn’t rec­og­nized through the other eye.) Binoc­u­lar vi­sion al­lows the horse to see the same thing with both eyes at once. With this wide range of vi­sion from monoc­u­lar and binoc­u­lar view­ing, horses can see more of the world around them at any given mo­ment than a hu­man. When your horse spooks or star­tles, it may be caused by some­thing you can’t see with­out turn­ing your head.

3. Blind spots. This eye place­ment also gives the horse blind spots—no­tably be­hind him­self and for a space of about 4 feet in front of him. To ad­just for this front vi­sion lim­i­ta­tion, a horse will nat­u­rally raise, lower or tilt his head to see bet­ter—which could ex­plain why so many horses re­flex­ively move their head up­ward as you raise a hand to their fore­head. It’s also worth not­ing that a horse rid­den with his nose on or be­hind the ver­ti­cal can­not see di­rectly in front of him­self.

4. Night vi­sion. Horses do have fairly good vi­sion in low-light con­di­tions. That’s be­cause their large eyes, com­bined with their hor­i­zon­tal pupils, help them cap­ture more light.

5. Color vi­sion. Horses can see some col­ors, although they prob­a­bly don’t see them as vi­brantly as peo­ple do. In gen­eral, they can see the green–yel­low spec­trum and the blue–gray spec­trum. They can’t see red.

6. Eye care. To help keep your horse’s eyes in good health, re­duce the chance of ir­ri­ta­tion from dust, in­sects and UV light. A fly mask may help as well as pro­vid­ing shade dur­ing peak sun­light hours. Also work to de­crease the risk of trauma by pay­ing at­ten­tion to sta­bling and pas­ture. Low tree branches, thorny plants, hooks or other sharp ob­jects can be haz­ardous.

7. Signs of trou­ble. If you no­tice that your horse is squint­ing, rub­bing an eye or sud­denly act­ing head shy, these could be signs of eye trou­ble. Also watch for tear­ing, squint­ing, red­ness, cloudi­ness or lumps and bumps around the eye. If you sus­pect a prob­lem, don’t hes­i­tate to call your vet­eri­nar­ian since treat­ment de­lays could in­crease the risk of a se­ri­ous is­sue.

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